Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy)

Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern... Landslides are among the most important and frequent natural calamities that cause severe socio-economic and human losses. After earthquakes, landslides are responsible for the greatest number of casualties and the largest amount of damage to man-made structures. On average, southern Italy is affected by a high spatial density of landslides due to its complex geological setting, which often predisposes it to slope instability phenomena under both natural and anthropogenic influences. Structurally complex formations are widespread in the southern Apennines and are characterized by high heterogeneity and very poor mechanical properties. Thus, these formations represent one of the main factors contributing to the predisposition of slopes to landsliding. In this paper, landslide-induced damage was investigated and analyzed in an area within the municipality of Agnone (Molise region), which is affected by a complex landslide that involves a structurally complex formation. The approaches used were based on six different methods that have previously been described in the literature, and a comparison of the results was made. Data regarding the damage, which consists largely of cracks observed in buildings and at the ground, were compiled through field surveys. The results were critically analyzed to note the advantages and constraints of each classification scheme. The aim of the work was to apply and compare different approaches in order to test the best and most accurate procedures for assessing damage due to landslides at the scale of individual buildings as well as to provide an objective assessment of the degree of landslide damage to structures and facilities. . . . . Keywords Landslides Structurally complex formations Damage classification Buildings Agnone Introduction hazard worldwide (Schuster 1996; Schuster and Highland 2001). They have potentially catastrophic effects and cause Landslides are gravity-controlled natural or anthropogenic considerable socio-economic damage as well as fatalities. processes that represent the most widespread geological Mass movements are caused by several predisposing and * Matteo Del Soldato Nicola Casagli matteo.delsoldato@unifi.it nicola.casagli@unifi.it Domenico Calcaterra Diego Di Martire domenico.calcaterra@unina.it diego.dimartire@unina.it Earth Sciences Department, University of Florence, Via La Pira 4, Silvia Bianchini 50121 Florence, Italy silvia.bianchini@unifi.it Department of Earth Sciences, Environment and Resources, Roberto Tomás University of Naples Federico II, Largo San Marcellino 10, roberto.tomas@ua.es 80138 Naples, Italy Pantaleone De Vita Departamento de Ingeniería Civil, University of Alicante, P.O. Box pantaleona.devita@unina.it 99, E-03080 Alicante, Spain Massimo Ramondini Department of Civil, Architectural and Environmental Engineering, massimo.ramondini@unina.it Federico II University of Naples, via Claudio 21, 80125 Naples, Italy M. Del Soldato et al. driving factors, including both natural and anthropogenic fac- The level of damage was assessed by means of different tors, such as deforestation or poor urban planning. existing methods developed in various contexts and for Anthropogenic factors are locally worse than natural ones different purposes. (i) The first method is based on the (Wu and Qiao 2009; Di Martire et al. 2012;Tofani etal. rehabilitation of the observable cracks (Burland 1977; 2013;Wuetal. 2015). Boscardin and Cording 1989); (ii) the second method was In Italy, population growth and the consequent expansion developed after an important landslide event in Italy of urban areas (Rybár 1997) have often induced people to (Alexander 1986); (iii) the third is focused on the survey build structures in areas over dormant landslides or at the of damage to buildings in landslide-affected areas edges of active landslide areas. Moreover, the disregard of (Chiocchio et al. 1997); (iv) the fourth approach is a the laws countervailed with several successive amnesties be- scheme realized by merging several damage classifications cause of infringement, in addition to the loss of memory of for use with subsidence, mining-related, and landslip past ruinous landslide events, have led to the development of events (Cooper 2008); (v) the fifth method (Baggio et al. facilities in hazardous areas, such as volcanic- or landslide- 2009) was proposed for post-seismic events by the Italian prone regions. Urban expansion can cause modifications to Department of Civil Protection (DPC hereafter); and (vi) hillslope morphology, inducing terrain remobilization and re- the sixth method is a recently published approach based on activation of old landslides that were previously dormant or the previous ones and was developed in two subsequent suspended, despite thousands of years of knowledge of nega- phases to assess the severity of cracks and constructions tive experiences (Chiocchio et al. 1997). (Del Soldato et al. 2017). Landslide-induced damages at Physical vulnerability, which defines the level of damage to the study site were recorded and assessed by means of critical infrastructures and buildings, is a key parameter in risk two field surveys conducted in November 2015 and in assessment. The occurrence of several landslides in urban July 2016. areas has highlighted the need to create a standard procedure The main aim of this work is to apply and compare to recognize and classify different levels of damage in order to different methods for classifying landslide-induced dam- help land management authorities (Alexander 1986)to focus age on structures and facilities in order to evaluate the and carry out mitigation strategies. Slope movements cause most accurate field procedure for the management and damage to buildings and other facilities and impose direct adoption of prevention and remedial measures through (e.g., replacement, repair or maintenance of damaged struc- a landslide case study in Agnone, Italy. The main advan- tures) and indirect costs (all other costs, which are difficult to tages and drawbacks of the different classifications are evaluate, e.g., losses of service) (Schuster and Fleming 1986; analyzed and discussed. Schuster 1996;Godtet al. 2000). These costs depend on sev- The paper is structured as follows: the next section briefly eral factors, including the dimensions and velocity of the mass describes the geological and geomorphological setting of the movement, the magnitude and type of the landslide mecha- Colle Lapponi - Piano Ovetta (CL-PO) landslide-prone area. nism, the lithology involved, the morphological features, and The presentation details of the different damage assessment the effects of anthropogenic activity. approaches applied for the categorization of the buildings and Attention is usually paid to planning strategies to prevent or infrastructures are given after that. Then the details of the field reduce urban landslide disasters, rather than evaluating their work developed for the classification of the damage and the impacts and the resulting damage. Maps illustrating the level recognized landslide-induced damage are described. of damage to affected buildings could provide an instrument Followed by a discussion of the main results obtained by to prevent the construction of facilities in historically applying the six methods. Finally, the main conclusions of landslide-prone areas. Furthermore, mountainous and geolog- the paper are summarized. ically complex environments characterized by the presence of structurally complex formations (Esu 1977), such as the southern Apennines, and associated with intense or prolonged Geological and geomorphological setting rainfall events, or to strong seismic shocks, are usually very prone to landslides. The study area (Fig. 1a) is sited in the western part of the This work addresses the description and classification municipality of Agnone (Molise, southern Italy) and is strong- of buildings and facilities damaged by the reactivation of ly affected by landslides and erosional processes. The CL-PO a slow-moving and intermittent landslide, known from the area is located in the catchment of the San Nicola Valley, a beginning of the XIX century, using six different damage sub-basin on the hydrographic right side of the Verrino assessment approaches. The landslide is located in the Torrent. municipality of Agnone (Molise region, southern Italy), The outcropping geological units include the Upper occurred in 2003, and involves Miocene-Pliocene clay- Miocene Agnone flysch (Sannitico-Molisane Formations) ey-marl lithologies. (Vezzani et al. 2004,Fig. 1b). This is characterized by Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 1 Location of the area of interest (a). Geological sketch map of the region of Molise (Vezzani et al. 2004) (b). The red line is the outline of the CL-PO landslide turbiditic siliciclastic deposits composed of alternating thin geotechnical campaigns in which four boreholes were drilled. layers of clayey sandstones, sandstones, and arenites They recognized four distinct layers (Fig. 2), described from (Filocamo et al. 2015). The CL-PO landslide involves the top to bottom as follows: upper member of the Agnone flysch, which is made up of marl, clayey, and subordinate grayish sandy levels with Level A – hard rock and mudstone fragments distributed low mechanical resistance and some alterations. Some throughout a chaotic and plastic clay matrix. Direct shear tests lithic intercalations, consisting of sandstone or calcare- performed on matrix samples indicated a peak friction angle ous levels with highly variable thicknesses, are also of approximately 19° and a cohesion of 20 kPa. This horizon present. The Agnone Formation is covered by a super- was directly involved in the 2003 reactivation of the CL-PO ficial regolith horizon composed of clay, silty clay, and landslide; occasional sand with diffuse alteration traces, abundant Level B – gray clay, silty clay, sandy clay, and silty sand. organic material, and some clasts. This layer displays medium plasticity and has a drained peak Calcaterra et al. (2008) performed a geotechnical charac- friction angle near 23° and a drained cohesion of approximate- terization of the landslide by means of several geological and ly 28 kPa; M. Del Soldato et al. Fig. 2 Engineering geological cross section passing through the median axis of the landslide with the locations of boreholes S1, S2, S3, and S4 modified from Calcaterra et al. (2008). A – hard rock fragments and clays; B – clays and sands; C – limestone level; D – marls and clays Level C – calcareous levels with thicknesses varying from The climate of the region is temperate with temperatures 0.1 to 1.0 m; ranging from 0 to 27 °C in winter and summer, respectively. Level D – marly clays, marls, and clayey marls with silt and Precipitation falls primarily during the rainy period from clay fractions. This horizon exhibits a plasticity comparable to September to April with an average monthly accumulation that of level B but with a drained peak friction angle close to approximately of 80 mm to which the snow must be added. 22° and a drained cohesion of approximately 60 kPa. During the summer season (from July to August) the accumu- lated rainfall is approximately 45 mm (http://www.regione. The main sliding surface is located at a depth of approxi- molise.it/schemiidrici). The morphology of the area has mately 25 m in the upper and central part of the landslide. The changed constantly over time as the reshaping of the earth depth of the surface of rupture considerably decreases in the surface has progressed due to the evolutionary stages of the lower portion of the landslide, in which the movement seems landslide (Fig. 3). After the reactivation occurred in 2003, an to evolve into an earth flow up to a few meters thick. important standing water body was identified in the middle Weathering effects, which consist of discolored, decomposed, portion of the landslide. This area is delimited by an important and weakened hard rocks, as well as scaly structures, were scarp and a counterslope, upstream and downstream, recognized in the borehole logs. An intercalation of fractured respectively, due to the geometry of the mass movement. and highly permeable calcareous beds, with thicknesses rang- The morphology of the area is flatter due to drainage works ing from decimeters to one meter, were observed (Calcaterra and the deposition of sediments transported by the surface et al. 2008). runoff. Other scarps that have been smoothed by erosional The ground morphology is controlled by the outcropping processes are clearly recognizable within the landslide area. lithotypes. Calcareous slopes show the highest gradients These scarps are located close to both flanks, as well as in the (close to 30–35°), whereas the argillaceous flysch units exhib- central and upper portion of the body of the mass movement. it slope gradients of approximately 5–10°. In areas where ero- The recognizable ground surface fractures were considered in sional processes are more significant, the steepness increases the classification as a relevant element for analysis of the to 15–20°. The 2003 CL-PO landslide developed along a extension and evolution of the gravitational phenomenon. slope sector that lies between 850 and 650 m a.s.l. and has a length of approximately 1500 m down to the confluence with Overview of the landslide inventory at Agnone the Verrino Torrent at 590 m a.s.l. The entire landslide area has an average slope of approximately 10° with peak values in the The availability of historical data, including information re- upper portion reaching 30°. garding localization and triggering factors, allows the Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 3 Decadal evolution of the CL-PO landslide. a) Mid-1990s, b) 2003, c) 2004, d) 2005, e) 2007, f) 2015 formulation of future realistic scenarios concerning the evolu- Reactivation of the CL-PO landslide tion of the slope instability (e.g., Calcaterra and Parise 2001; Calcaterra et al. 2003) and the detection of potential After an intense rainfall event that affected southern Italy be- reactivations and impacts of the phenomenon. tween the 23rd and the 27th of January 2003, with more than Landslides have been known in the municipality of 200 mm of rain falling over 72 h, the investigated area was Agnone since at least the beginning of the twentieth involved in an important reactivation of a dormant historic century. The oldest report describing an instability event landslide due to an unusual increase in pore pressure refers to a phenomenon that occurred in March 1905 in (Calcaterra et al. 2008). In the municipality of Agnone, a cu- the San Nicola Valley due to the combination of a pe- mulative precipitation of approximately 50 mm was measured riod of intense rainfall and snowmelt (Calcaterra et al. in the meteorological station located in CL-PO (Lat 41.80° 2008,Fig. 4a). This event damaged the bridge that car- and Long 14.33°) belonging to Regional Agency for the ried the main access road to the historical center of Agricultural, Rural and Fishing Development (Agenzia Agnone (Almagià 1910). Regionale per lo Sviluppo Agricolo Rurale e della Pesca - The municipality of Agnone has been successively ARSARP - www.arsarp.it/agromtorologia)inthe same affected by several small and large landslide events. period in which a reactivation of the landslide (Calcaterra et Archival and bibliographical landslide research, reported al. 2008), with a complex style consisting of a succession of in the nationwide AVI Project (Guzzetti et al. 1994), large roto-translational slides by an earth-flow (Cruden and revealed more than 60 landslides that occurred in the Varnes 1996). The event involved several facilities, forcing municipality of Agnone and the surrounding territory the municipality’s administration to adopt restrictive mea- from 1970 to 1998. In February 1984, a mass move- sures, i.e., the evacuation of 13 buildings located in the area ment occurred close to the study area that affected two involved in the landslide, in which 17 families were living. pillars of the viaduct of a State Road (Guadagno et al. The municipal administration, owing to the severity of the 1987), forcing the demolition of a section of it (Fig. situation, earmarked funds to perform several urgent interven- 4b). In 1994, a mass movement affected the Colle- tions, such as the re-shaping of the area affected by the mass Lapponi area, causing the interruption of a dirt road. movement and the excavation of a trench in the upper part of Finally, the latest landslide inventory of the municipality of the body of the landslide in order to intercept and drain the Agnone was conducted by the IFFI Project (Italian Landslides water table, which locally reached the ground surface. Inventory Project) by ISPRA (Istituto Superiore per la During the years following the main reactivation, despite Protezione e la Ricerca Ambientale)in2008. the adoption of the abovementioned remedial measures, the M. Del Soldato et al. Fig. 4 Excerpt of the map published by Almagià (1910). The red box indicates the location of the CL-PO landslide (speckled in the figure); b) demolition of the State Road viaduct following the 1984 landslide (from Guadagno et al. 1994) entire landslide remained active, increasing its dimensions and topographic measurements were conducted using GPS equip- causing additional damage to facilities and buildings. During ment to evaluate the progressive evolution of the landslide and March 2004 and in the period between December 2004 and the enlargement of the main scarp. These data confirmed the January 2005, the landslide was reactivated by a series of effectiveness of the stabilization works in the central and low- heavy rainfall events (Fig. 5), increasing the area involved er sectors of the landslide, but not in the upper area. 6 3 and mobilizing an estimated total volume of 3.5 × 10 m Furthermore, in 2012, eight corner reflectors were installed (Calcaterra et al. 2008). on the mass movement to monitor the landslide (Di Martire Continued advancement of the movement that resulted in et al. 2013) by means of Differential Interferometric Synthetic progression of the landslide foot over approximately 70 m was Aperture Radar (DInSAR) techniques. recognized by June 2006, and a lower displacement rate was In November 2015 and July 2016, additional field surveys detected between April 2006 and April 2007. These observa- permitted the examination of the further evolution of the slope tions led to the adoption of new mitigation measures in the movement and the identification of a new boundary of the middle part of the mass movement, where ground subsidence landslide (red line in Fig. 6) as well as many tension cracks and the collection of surface runoff formed a landslide lake. inside and outside the landslide boundaries. The field cam- Consequently, additional reshaping of the slope and the exca- paigns were mainly devoted to identify, record, and assess vation of 10 trench drains (6.5 m deep and approximately the severity of the landslide-induced damage on several facil- 150 m long) were performed. These actions stabilized the ities located within and close to the landslide. middle to lower parts of the mass movement. From 2004 onward, a set of topographic benchmarks were placed within the unstable areas to monitor the surficial movement of the Methodologies for damage assessment landslide. From 2004 to 2011, the landslide advanced approx- imately 350 m at the toe and retrogressed approximately Displacements that occur in landslide areas are often revealed 270 m in the head sector, increasing the total length to as fractures on the ground surface or as ruptures and cracks in 1500 m (Fig. 6). In 2010 and 2013, two campaigns of man-made facilities. These effects appear when ground Fig. 5 Daily (blue bars) and cumulative (green line) rainfall from (a) December 2002 to January 2003 and (b) from December 2004 to January 2005. The red box highlights the rain event, which caused the main reactivation of the landslide (www.arsarp.it/agromtorologia) Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 6 Evolution of the boundaries of the CL-PO landslide from 2004 to 2011. Ground evidence recognized during the 2015 survey is drawn in red movements that affect the buildings are greater than the tensile The scientific community has developed some specific stresses that the structures are capable of accommodating classifications of damage for areas affected by natural cata- without apparent deformation. The first elements to reveal strophic phenomena, such as earthquakes (e.g., Wood and damage are the most rigid ones, such as walls and façades, Neumann 1931;Medvedev 1965; Grünthal 1998), subsidence or the weakest elements, such as joints (Bru et al. 2013). (e.g., Van Rooy 1989; Howard Humphreys & Partners, 1993; Building damage is commonly assigned to three general cat- Freeman et al. 1994), and landslides (e.g., Burland 1977; egories: architectural, functional, and structural damage. Alexander 1986; Geomorphological Services LTD, 1991; These categories were first disseminated by Skempton and Lee and Moore 1991; Chiocchio et al. 1997;Iovineand MacDonald (1956), who did not define clear boundaries be- Parise 2002). tween them. Architectural damage refers to the appearance of In this work, six different methods were used for classify- a structure (e.g., fine cracks in finishes, floor or panel walls, ing the observed damage to the facilities affected by the CL- cracks wider than 0.5 mm in plaster or wider than 1 mm in PO landslide. The methods include those of (a) Burland rough concrete and masonry walls). Functional damage af- (1977), slightly modified by Boscardin and Cording (1989), fects the use of the structure and produces extensive cracks, (b) Alexander (1986), (c) Chiocchio et al. (1997), (d) Cooper tilting of floors and walls, falling plaster, obstructed doors and (2008), (e) the DPC (Baggio et al. 2009), and (f) Del Soldato windows and other non-structural damage. Structural damage et al. (2017). The main characteristics and differences between reduces the stability of the structure manifesting as ruptures the different classifications are summarized in Table 1.The and distortions in support elements (e.g., pillars, columns and application of the six different methods of classifying the load-bearing walls). In practice, damage affecting facilities landslide-induced damage allows defining the most appropri- have to be assessed by performing field surveys, which are ate approach for this case study. This is useful for several highly conditioned by the criteria adopted and the experience purposes, such as civil protection management after signifi- of the operators. cant events, urban planning and managing of remedial and M. Del Soldato et al. Table 1 Main characteristics of the applied methods to classify the landslide-induced damage on structures (updated from Del Soldato et al. 2017) Burland et al. Alexander Chiocchio et al. Cooper DPCBaggio et al. Del Soldato et al. Year 1977 1986 1997 2008 2009 2017 Number of classes 6 8 8 8 4 8 Distinction of structure NO NO YES NO NO YES Reference values YES (mm) NO YES (cm) YES (mm) YES (mm) YES (mm) Partition of the structure NO NO NO NO YES YES Applicability on ground surface NO NO NO YES NO YES Note: ND means Bnot defined^ prevention measures, and architectural and engineering 1994;Iovine and Parise 2002). These include, for example, design. the type and age of construction of the buildings or the reno- vation works (Chiocchio et al. 1997). Burland 1977 Chiocchio et al. (1997) The simple approach presented by Burland (1977) was de- rived from the accumulated experience of the author in the Chiocchio et al. (1997) defined a new classification of land- field through three previous studies: i) a study of the economic slide damage to buildings that overcomes some of the draw- consequences on the heaving of construction on swelling clay, backs that were identified in the classification of Alexander by means of a simple classification of damage based on the (1986). The new approach was conceived thanks to an inter- ease of restoration (Jennings and Kerrich 1962); ii) a simple disciplinary effort involving geologists, geomorphologists, classification based on wide experiences in subsidence dam- and civil engineers. age (National Coal Board, 1975); and iii) a categorization This classification considers two different types of struc- structure-soil interaction proposed by the Coal Board’srecom- tures (i.e., masonry and reinforced concrete) and provides mendations (MacLeod and Littlejohn 1974). Burland’s(1977) quantitative reference values for some parameters. These im- classification is divided into six damage classes based on the provements were relevant to the analysis of the fractures to width of cracks and related to the ease of restoration. Within allow evaluation of similar cracks in different materials and to these classes, the widths of the cracks are approximate. minimize the subjectivity of the survey. The damage level was The measurement is related only to visible or esthetic dam- divided into eight different grades and, additionally, some age, observed corrosion, and cracks permitting the penetration general recommendations for rehabilitation measurements or the leakage of liquids or gases. For reinforced concrete, the were defined. The first three levels correspond to negligible adopted approach should be more severe (Nawy 1968). and weak damage; buildings affected by the fourth grade of damage exhibit some serious cracks, and restoration strategies Alexander (1986) are suggested for them; the fifth grade is characterized by several failures that affect the structure and the surrounding After an important landslide event occurred in Ancona, central area. The last class is assigned to buildings in which the level Italy, in 1982 an alternative intensity scale of damage was of damage is so severe that the extent of the damaged area has developed (Alexander 1983). This method referred to the to be accurately evaluated in order to decide whether to reno- landslide-induced damage observable on buildings and per- vate or relocate the entire construction (Chiocchio et al. 1997; mitted the comparison of the damage observed on different Iovine and Parise 2002). structures involved in the event. The proposed scale refers to landslide damage due to subsidence, rotational and transla- Cooper (2008) tional movements, and slow thrusts rather than to the impact of the avalanching debris (Alexander 1986). This approach The classification is formulated on the basis of several previ- includes eight damage levels based on the severity and wid- ous classifications for evaluating building damage caused by ening of cracks, the distortion of rigid elements and the degree subsidence and landslides. The affinity between several of settlement that affects the foundations in addition to two of existing schemes for recording damage caused by landslides which correspond to the most severe categories, i.e., partial and subsidence permitted the generation of a single scheme and total collapse of the structure, based on the cracks ob- that describes observable damage to buildings, independent of served on walls. However, some missing features of this meth- the causes (Cooper 2008). This classification also divides the od have been identified during applications (Crescenzi et al. severity of the damage into seven classes, from very slight to Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) total collapse, in addition to a class describing negligible dam- of this approach with respect to the previous approach is the age. The definition of the categories was based on studies by introduction of the extent of damage. the National Coal Board (Handbook 1975), Alexander (1986), For the aim of this work, only the two sections related to Geomorphological Service Ltd. (1991), Freeman et al. (1994), recording structural and non-structural damage were considered, the Institution of Structural Engineers (1994), and Chiocchio in addition to the introduction of the evaluation of the extension et al. (1997). of the cracks as affecting less than 1/3, a portion between 1/3 and In this classification, ground damage caused by landslides 2/3, or more than 2/3 of the building for each class of damage. and subsidence were included considering that most of the Accordingtothisapproach,the investigation of structures has to survey was performed by studying the external façades of be ideally divided in three parts considering intervals of 33% or buildings. In this approach, damage to roads and other facili- 67%. Additionally, the magnitude of the damage that affects ties can also be surveyed and could even be evaluated (Cooper each part of the structure can be assessed as null (D0), weak 2008). Cracks and fractures observed on facilities and the (D1), medium-severe (D2-D3), and very severe (D4-D5). The ground surface are related to more severe damage classes sum of the extent of the damage cannot exceed 1, representing (above the third grade). the entire building (e.g., 2/3 of D4-D5 + 1/3 of D2/D3). The damage grades are described by a scheme without The DPC classification was originally developed to evalu- details on cracks in foundations or other subsurface features, ate the fitness for human habitation of buildings after a seismic as Cooper (2008) considered that the recording of damage event. Therefore, for comparing the results obtained by this using more practical parameters has proven to be popular, approach to the others mentioned above, a further consider- simple, and easily performed in field surveys. ation was necessary to have the same number of classes. All possible combinations, considering the extent of the damage The Italian Department of the Civil Protection for each class and the four classes of cracks (D0, D1, D2-D3, approach (Baggio et al. 2009) D4-D5), were considered. Then, a conversion matrix was used to evaluate the seriousness of the damage affecting a single This method was conceived for surveying damage that affects unit according to the possible combinations of damage. For civil construction after seismic events in order to assess the each level of damage, a value was assigned and then grouped fitness for human habitation of the buildings. The applicability into eight classes varying from 0 (negligible damage) to 7 to landslide phenomena is derived from the causes of the (total collapse) in order to compare the resulting map with damage due to the effects of shear stresses in both cases. the other described classifications. This method was applied in several field situations involving seismic events in Italy (e.g., 1980 Irpinia earthquake in Del Soldato et al. (2017) Campania, the Abruzzo region in 1984, and the Basilicata region in 1990) and it was tested in subsequent earthquakes This classification was developed through the application and (e.g., the Umbria-Marche regions in 1997, and Pollino and the analysis of results of previous approaches to provide a rapid Basilicata-Calabria regions in 1998) with the view to enable evaluation of cracks and fractures during field surveys and a making judgements on the ability of structures to host their subsequent assessment of the buildings damage caused by inhabitants safely, so it does not address protection of the landslides. To create this new classification method, several structures. landslide-induced categorizations of damage to buildings This approach was devised to perform initial classifications were considered (Burland 1977; Alexander 1986; Chiocchio of damage magnitudes by means of quick surveys. It was et al. 1997;Cooper 2008) jointly with the approach for the conceived to assess the reliability of structures. Therefore, assessment of seismic event effects developed by the DPC the recording scheme for the damage is more complete than (Baggio et al. 2009) to insert the importance of the extension the one presented previously. It is composed of several tables of the cracks and fractures in the damage evaluation. suitable for emergency post-seismic event surveys. Overall, Furthermore, similar to the Cooper (2008) approach, external this recording scheme is composed of nine sections: a) three recognition plays a key role, and the ground fractures are also tables devoted to the identification and description of the ex- considered. Ground cracks are not considered related to the amined buildings; b) two sections referred to a quick assess- constructions, but singularly, in order to implement the knowl- ments of structural and non-structural damage; c) a section edge regarding severity and extension of the landslide effects. dedicated to evaluating the possible involvement of surround- The classification is divided into six ranks from no damage to ing structures in case of the collapse of edifices; d) a section very severe. In this categorization, the collapse is not consid- that addresses the geomorphological condition of the terrain ered because in the first phase the focus is the network of surrounding of the buildings; e) a section to assess the build- cracks and fractures that affect the structures. Subsequently, ing’s conformity with standards; and f) a final section to in- the extent of the damage has to be considered and, by means clude notable and useful information. The main contribution of a matrix, the entire building could be classified into eight M. Del Soldato et al. classes from Bno damage^, meaning safe construction, to These types of fractures on roads and ground surfaces Bunusable^, indicating an uninhabitable building. (Fig. 10) are investigated and classified only by the most recent approaches proposed by Cooper (2008)and Del Soldato et al. (2017). The identification and survey of these Description and classification of damage fractures, the assessment of their severity, and the investiga- tion of their probable correlation to the activity of the land- The January 2003 landslide reactivation was the most recent slide, can be important parameters to support the identification event that caused serious damage to facilities and buildings in of extension of the landslide-prone area. Agnone. Damages were chiefly related to the loss of support to An example can be made taking into account a sidewalk structures due to the downward and outward movements of the made of reinforced concrete (Fig. 10) that is located in the foundation zones (Hunt 2005). This effect was important for present crown of the landslide that currently shows an impor- forcing the administration of the local municipality to take some tant open crack pattern with detachment of a portion restrictive measures, such as a precautionary evacuation of sev- (Fig. 10b). In recent years, the crown of the landslide has eral houses located close to the area that were affected by the retrogressed, widening its boundaries and increasing its di- slope movement. In November 2015 and July 2016, forensic mensions, as reflected in the opening of new tension cracks analyses were conducted for 30 buildings, two walls, and three and the collapse of a part of the sidewalk bordering a building concrete surfaces near the landslide; one electric tower close to that does not show severe damage to the external façades. its left flank; and several tension and shear cracks on ground The in situ analyses provided qualitative and quantitative surface and pavements. For this purpose, external damages were information about the fractures used for damage assessment of surveyed using a regular scheme (see supplementary material by the studied elements, according to the six classifications de- Del Soldato et al. 2017) in order to collect as much information scribed earlier (Table 2 and Fig. 11), one for each methodol- as possible: i) date and site of the survey, hamlet, municipality, ogy applied to record the damage to the facilities located with- and province; ii) identification number of the structure under in the landslide-prone areas. It is worth noting that, although investigation; iii) coordinates of the façades; iv) type of con- these methodologies were originally proposed for the identi- struction, e.g., buildings, gymnasium; v) load-bearing materials, fication of damage to buildings, in this work they were also e.g., masonry or concrete; vi) date of construction and number of applied to categorize other man-made elements (i.e., an elec- floors of the edifice; vii) position with respect to the landslide; tricity mast, two walls, and three concrete areas) that were viii) draft and classification of the ruptures of on ground and strongly affected by ruptures. The results show that most of pavement; ix) drawing and categorization of cracks on build- the damage is located in areas where the landslide remains ings; x) extension of the damage in all structures or only in its active. Several structures, buildings and infrastructures, in portion; and xi) georeferenced photographs. The procedure for and close to the mass movement, therefore, within the land- collecting such information is considered important inasmuch slide prone-area, were investigated (Fig. 11a). that the same opening, or two similar cracks, in two structures built with different materials could have different meanings (Chiocchio et al. 1997; Iovine and Parise 2002). Results Different levels of damage that affect the buildings are grouped into several types: In this section, the results derived from the damage assessment of the building and the infrastructures placed in CL-PO land- & hairline cracks (Fig. 7a); slide by means of the different approaches described earlier & open fractures on external walls (Fig. 7b and c); are presented. & ruptures between walls and external pavements (Fig. 7d Following the classification of Burland (1977)(Fig. 11b), a and e); and large number of buildings (approximately 50%) present Slight & in rare cases, roof collapses (Fig. 7f). and Very severe damage, as several abandoned structures are strongly affected by damage and have partially collapsed. In concrete sidewalks and walls, the following elements Only two buildings have been assigned to the Negligible class, were investigated: and four fall into the Very slight class. Negligible damage were observed in more recent structures, in a small house that was – hairline cracks (Fig. 8a and the red arrow in 8c) and probably renovated in recent times and in buildings that were – open cracks (Fig. 8b–d). built further from the landslide than the others. The Very slight class includes a building located on the present-day crown of Cracks recognized on the ground (Fig. 9b) or on pavements the landslide. This rank is due to the low level of damage (Fig. 9a) were plotted on a topographic map and photographed present in its façades, although important damage could affect as well as spatially identified with a GPS tracker. its foundation. Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 7 Damage identified on buildings. a) Hairline crack in the plaster of and the pavement in a masonry building; e) open crack, more than a masonry wall; b) open crack, approximately 1.0–1.2 cm wide, in a wall 10 cm wide, between a wall and the ground surface of a reinforced of a reinforced concrete building; c) open crack, approximately 4 cm concrete building; f) collapsed roof in a masonry building wide, in a wall of a masonry building; d) open crack between a wall Alexander’s(1986)(Fig. 11c) classification measures existing high risk. Another noteworthy point is that this crack apertures in centimeters instead of millimeters. This methodology considers two categories for buildings that implies that the classification is less sensitive to damage, are strongly affected by damage: Partial collapse and Total and most of the facilities are grouped into the Light and Collapse. The nine buildings assigned to the Very severe class Moderate classes. Additionally, in this classification, using the Burland (1977) approach are divided into three clas- Bevacuation and rapid attention to ensure^ is recommended ses according to Alexander’s(1986) classification: three of the for those facilities that exhibit Moderate damage. Concerning buildings fall into the Very serious class, five fall into the the buildings located on the crown of the landslide, this meth- Partial collapse rack, and one falls into the Total collapse odology classifies the damage as Negligible, despite the category. Fig. 8 Damage recognized on concrete slabs and walls. a) Hairline crack in pavement; b) open rupture in a slab; c) hairline (red arrows) and open fractures in a concrete wall; d) damage to a masonry wall M. Del Soldato et al. Fig. 9 Cracks located close to the landslide on (a) the pavement of a road and (b) the ground surface. In photograph (b), a vertical slip is recognized The Chiocchio et al. (1997)(Fig. 11d) approach also mea- sensitivity in assessing damage that is caused by the use of sures cracks in walls using centimeters. However, this ap- the millimeter as the unit of measurement, and it is a more proach includes the construction distinction between masonry appropriate methodology for classifying ruptures that affect and reinforced concrete, in contrast to the previously men- some facilities, such as pillars, walls, and concrete sidewalks. tioned methodologies. In this way, structures affected to a The DPC approach (Baggio et al. 2009) divides the level of significant degree by rigid settlement, which were previously damage into four classes, although the classification includes assigned to the low damage classes, are grouped with those eight damage classes: two low levels (None and Negligible), affected by several cracks. A concentration of buildings is four categories representing significant damage (Severe, Very assigned to the Light and Moderate damage classes, and the severe, Partial,and Total collapse), and two intermediate authors suggest evacuation even for the Moderate category. grades (Slight and Moderate)(Fig. 11f). This approach pro- Moreover, it is important to note that using this categorization, vides a more evenly distributed classification of damage (thus the building (B01) located on the probable present-day crown most of the buildings are not ranked into only one or two of the landslide has few, narrow visible cracks in its external classes) than the previous described and applied approaches. façades, perhaps justifying the low damage classes assigned Despite the small number of facilities located in the study area, by the classification, despite an important rupture that affects an increasing number of structures are ranked into the catego- the front concrete sidewalk. Six buildings, probably aban- ries reflecting high levels of damage (Severe and Very severe). doned several years before the main event, are assigned to This methodology gives more attention to damaged buildings the highest categories of damage (i.e., Partial collapse and since it was conceived to evaluate the fitness for human hab- Total collapse), as in the Alexander (1986) approach. itation of structures after a damaging seismic event. The Del Soldato et al. (2017) categorization provides a In his approach, Cooper (2008)(Fig. 11e) introduces the description and categorization of landslide ground damage in homogeneous distribution of the structures located in the addition to the classification of the damage recognizable on landslide-prone area due to its simple but detailed approach facilities and buildings. This classification uses millimeters to that includes two phases. These two steps of damage measure the opening of the cracks that appear on the elements evaluation and subsequent structure assessment in sensu of the investigated structures. In our case study, the classifica- stricto allow a better discrimination of the severity of cracks tion assigns an important number of buildings to Class 3, and fractures. Similar to the Cooper (2008) approach, the in- compatible with the Moderate category of the other ap- vestigation takes into account the external portions of the proaches. Comparing the proposed classification with the oth- structures eliciting an increment in the low ranks of the build- er areas, more facilities are sorted into the higher levels of ings affected by weak fractures in external facades but rele- damage. This is probably due to the method’s higher vant fractures and displacement in the foundations. Several Fig. 10 Evolution between 2003 (left) and 2015 (right) of a rein- forced concrete perimeter side- walk of a building located on the crown of the landslide Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Table 2 Summary of the damage assessment in the different location of the study area ID Structure type Position respect Damage description Damage classification to the landslide Burland 1977 Alexander 1986 Chiocchio 1997 Cooper 2008 DPC 2009 Del Soldato 2017 B01 CS CR Sparse thin cracks in the facades; several 21 1 2 2 3 fractures between the walls and the sidewalk. B02 CS CR Rare thin cracks mainly starting from the 53 3 3 3 5 corner of the doors or windows. An important open rupture (up to 10 cm) affecting the foundation is visible on the south-eastern corner B03N MB CR Negligible cracks and one joint in the 01 1 1 1 2 connection area with the B03S B03S MB CR Some thin cracks around the doors and 22 2 2 3 3 windows and an open joint in the connection between this construction and the connected B03N B04N MB FL Several thin, open and filled cracks; one 34 4 4 5 5 important disjunction affecting a railing in bricks. Roof weakly bent and several cracks between the walls and the external sidewalk. Connected with the B04S B04S MB FL Some very important ruptures (up to 5 cm) 56 6 6 6 7 and roof collapsed. Connected with the B04N B05N MB FL Several open cracks (up to 2 cm) mainly in 53 3 5 5 6 the eastern façade and close to doors, windows and the terrace; very open joint between these buildings and the connected B05S B05S MB FL Some open cracks on column and starting 43 3 4 4 5 from doors and windows, roof weakly bent, very open joint in the connection area with B04N B06N MB CR Diffuse open cracks (up to 1 cm) in the south21 1 1 1 2 part of the east exposed façade, sparse thin cracks in the entire construction, important swelling in the retaining wall. B06S CS CR Diffuse very thin fracture affecting only the 43 3 4 4 5 plaster B07 CS CR No cracks and damage 0 0 0 0 0 1 B08E MB CR Important open joint (up to 3 cm) crossing an45 4 5 5 7 entire façade, other thin ruptures, partial collapse of a roof. Connected with the B08W and B08S without joints B08W MB CR Several open cracks (up to 1.5 cm) close to 34 3 4 4 5 the windows and door in one façade, in the other one only two ruptures (one open M. Del Soldato et al. Table 2 (continued) ID Structure type Position respect Damage description Damage classification to the landslide Burland 1977 Alexander 1986 Chiocchio 1997 Cooper 2008 DPC 2009 Del Soldato 2017 about 1 cm and one recently filled). Connected with the B08E and B08S without joints B08S MB/CS CR Few thin cracks starting from doors or 22 2 2 2 3 windows boundary. Connected with B08E and B08W without joints B09W MB CR Some vertical open cracks (up to 1 cm), 33 3 4 3 5 bending of the beam and little distortion of the north-east corner of the roof. Connected with B09E and B09S with thin joints B09E CS CR One vertical open crack (up to 1 cm), several24 3 3 3 4 thin ruptures close to doors and windows and in facades, some cracks between the walls and the external sidewalk. Connected with B09S and B09W with thin joints B09S MB CR Some vertical thin joint reflecting, probably, 32 2 3 2 5 several subsequently adding from the construction and close to doors or windows, roof slightly bent in a central region. Connected with B09E and B09W with thin joints B10 CS CR Very few hairline cracks in a façade affecting11 1 2 1 2 the plaster and in a corner between the external wall and the sidewalk B11N CR Some thin cracks between the external wall 12 1 1 1 3 and the sidewalk, rare fractures in the facades. Connected with B11O along an open joint B11O MB CR Diffuse thin cracks, some filled, close to the 23 2 3 3 4 doors and windows and between the external walls and the sidewalk. Connected with B11N along an open joint B12N MB FL Some thin crack around windows and tracing22 2 2 2 2 the line of the roof. Connected with B12N by a thin joint B12S MB FL Two fracture in the external stairs structure 12 2 2 2 3 and some think cracks close two windows. Connected with B12S by a thin joint B13m MB FL Rare hairline cracks affecting the facades. 22 2 3 2 2 Connected with B13S through thin and filled joints and with the B13N by open joints B13N MB FL Severe affected by cracks and open fractures35 5 5 5 7 vertically and close to the doors and Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Table 2 (continued) ID Structure type Position respect Damage description Damage classification to the landslide Burland 1977 Alexander 1986 Chiocchio 1997 Cooper 2008 DPC 2009 Del Soldato 2017 windows, open joint between the external walls and the sidewalk. Some of them are filled and signs of renovation are visible. Connected with the B13m by open and filled joints B13S MB FL Rare thin cracks on facades and filled ruptures12 2 2 2 3 between external wall and sidewalk. Connected with B13m through thin and filled joints B14 MB FL Almost totally collapsed (roof and floor) and57 7 7 7 8 wall twisted. B15E MB CR Partially collapsed (roof) and several cracks 34 4 5 5 8 on facades. Connected with the B15m by open joints. B15m MB CR Partially collapsed (roof) and several cracks 56 6 6 6 8 on facades. Connected with B15E and B15W by open joints B15W MB CR Partially collapsed (roof) and several cracks 56 6 6 6 7 on facades. Connected with the B15m by open joints B16 MB CR Diffuse open cracks (up to 1.5 cm) and roof 34 4 4 4 6 visible bent. E01 Steel FL Structure not affected by damage, but 23 3 4 4 6 foundation partially exposedbymeans of the boundary of the landslide S01 CS CR Diffuse thin cracks, some open rupture, partial56 6 7 7 7 region collapsed. Several cracking affecting the connection with the external wall of B01 S02 CS CR Diffuse very open cracks (up to 5 cm) and 56 6 7 7 6 filled ruptures S03 MB/CS FL Diffuse very open cracks (up to 5 cm) and 44 5 6 5 7 filled ruptures, tilting of parts of concrete andhole inthe surface W01 CS CR Several open cracks (up to 1 cm) and 43 3 5 4 6 horizontal and vertical distortion W02 MB CR Two main open cracks (up to 5 cm) and 55 5 7 6 6 horizontal and vertical distortion See location in Fig. 11 CS - reinforced concrete/steel; MB - masonry/bricks CR - crown; FK - flank - TO toe M. Del Soldato et al. Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 11 a) Localization of the investigated buildings and facilities with some families from their dwellings due to the serious damage their damage classifications according to b) Burland et al. (1977), c) that was caused to some structures. Despite the realization of Alexander (1986), d) Chiocchio et al. (1997), e) Cooper (2008), f) DPC relevant stabilization works in the landslide body, the follow- (Baggio et al. 2009), g) Del Soldato et al. (2017) ing years exhibited an enlargement of the dimensions of the landslide. The advancement of the toe and retrogression of the constructions are categorized in the low ranks of damage main scarp, with consequent involvement of the lateral flank (Negligible and Weak), and a relevant number is characterized to accommodate the movement, represents a threat of damage by important damage (Moderate and Severe). In the left flank to facilities and buildings located in the surrounding area. of the landslide (i.e., area 2), the constructions are categorized This paper focused on the comparison of six different with a high level of damage (Severe and Very severe)due to methods of landslide-induced damage classification for facil- the important displacement caused by a double component of ities and buildings located in a landslide-prone area, a funda- movement. The first displacement component affects the right mental parameter to prioritize further investigations. The clas- side of the study area that is under the influence of the CL-PO sification step can help local administrators decide where landslide. The second component is due to an enlargement of more detailed structural analyses should be performed or the mass movement that affects the neighboring basin. The where further actions must be considered. Furthermore, in three sidewalks and the two investigated walls are all catego- emergency cases, this preliminary structure classification rized into a high level of damage (Severe and Very severe)due may be sufficient to support the order of some restrictive mea- to the open cracks and fractures that affect them and, in one sures, the fulfillment of practice repairs or reinforcement of the case, the detachment of a portion of the sidewalk due to the main damaged structures. For this purpose, six assessments of regression of the landslide border. Only one edifice is featured landslide-induced damage approaches (Table 3)wereapplied by No damage due to its recent construction or renovation. and compared. The six classification methods, which seemed Three structures are classified as Total collapse: two of them, to be very different from each other, were found to have strong both abandoned, are close to the crown, whereas the third is similarities. In addition to a general comparison, two build- close to the left flank of the landslide. ings, one located upslope with respect to the crown of the CL- In addition to the structures, walls and sidewalks, an elec- PO landslide and the second on its left flank, were chosen to tricity mast located on the left boundary was investigated in analyze and discuss in detail the application of the features of order to assess its safety due to its important function for the the different methodologies for assessing landslide-induced surrounding edifices. This element is a steel rigid structure, damage. founded on a concrete sidewalk. The approaches proposed by The first building (Fig. 12a) is located on the present-day Burland (1977), Alexander (1986), and Chiocchio et al. crown of the landslide, as indicated by a significant ground fissure that cuts across under the entire structure. The displace- (1997) assign this facility to the medium level of damage, despite the displacement observed on the south-eastern side ment affects the building’s foundation and is easily recogniz- of its foundation. However, the DPC (Baggio et al. 2009), the able in the building’s southeastern corner (red circle in Cooper (2008), and the Del Soldato et al. (2017) methods Fig. 12a) by an evident opening with respect to the ground classify the damage to this facility as very severe. The stability up to 10 cm/year. The six applied approaches evaluate the conditions of the pillar base are characteristic of problems that damaged structures differently, depending on the element on affect structures located close to the landslide crown or flanks which they are focused. However, all of them assessed the (e.g., the two buildings located at the top of the landslide- damage level as Moderate, except the classification developed prone area). The lateral boundary of the landslide is located by Del Soldato et al. (2017). The method proposed by Burland under the electricity mast, as seen from the ground displace- (1977) does not consider ruptures involving building founda- ment on one side of the mast, whereas no signs of movement tions but only the cracks on the façades. In this case, aside are present on the other side. from the considerable ground fissures that threaten the foun- dations, no heavy relevant damage to the façades were sur- veyed. Alexander’s(1986) classification mainly considers the Discussion degree of settlement that affects structures instead of the wide cracks that may exist in the walls or structural elements, but Several landslides affect the municipality of Agnone (Molise given the complexity, the structure was assessed with the same region, southern Italy) according to the historical investiga- entity of damage. The method suggested by Chiocchio et al. tions and reconstructions described in the literature. In 2003, (1997) considers both the degree of settlement that affects the CL-PO area was affected by an important reactivation of structures and recognizable fractures on the façades. The low an old intermittent mass movement, attracting public attention level of damage to the external walls compensates for the because of the severe damage caused to surrounding buildings substantial and continuing displacement that affects the foun- dations of the building, reducing the severity of the and facilities. The local authorities were forced to evacuate M. Del Soldato et al. Table 3 Equivalence of the damage categories considered by the different classifications Burland, 1977 Alexander 1986 Chiocchio et al., 1997 Cooper 2008 DPC Baggio et al., 2009 Del Soldato et al., 2017 0 Negligible 0 None 0 0 0 None 0 None G0 No damage 1 Very slight 1 Negligible 1 Negligible 1 Negligible 1 Negligible G1 Negligible 2 Slight 2 Light 2 Light 2 Light 2 Light G2 Weak 3 Moderate 3 Moderate 3 Moderate 3 Moderate 3 Moderate G3 Moderate 4 Severe 4 Serious 4 Serious 4 Serious 4 Severe G4 Severe 5 Very severe 5 Very serious 5 Very serious 5 Very serious 5 Very severe G5 Very severe 6 Partial collapse 6 Partial collapse 6 Partial collapse 6 Partial collapse 7 Total collapse 7 Total collapse 7 Total collapse 7 Total collapse classification to the Moderate class instead of a worse class, as categorized the structure as Severe due to the typology, entity, would be expected. Cooper’s(2008) approach, in contrast to and extent of the damage. the previous two classifications, only considers the width of In summary, although the six methods focus on different the cracks that affect the external façades of structures. features caused by the movement that influences the structure, However, although this approach does not consider the settle- the damage was classified as Moderate, except for the Del ment that affects the internal or hidden portions of the struc- Soldato et al. (2017) approach that considers it as Severe, tures, it categorizes this building as Class 3 (comparable to a reflecting some consistency in terms of the damage Moderate) on the opening and the frequency of the cracks. assessment. The DPC method (Baggio et al. 2009), which also considers The second building is located on the left flank of the land- the extension of damage that affects the structures, allows a slide and is formerly connected to another adjacent structure more precise assessment of the damage. The structure shows but is now separated by a gaping construction joint (blue ar- cracks assessed as very important (D4-D5) for one portion rows Fig. 12b). The building is currently abandoned, the dam- and, for the remaining 2/3, occasional cracks (D1). To evalu- age to the structure includes relevant (e.g., see the red arrows ate the edifices sensu strictu, the conversion matrix combines in Fig. 12b) and open cracks and distortions of walls and the different contributions from the severity and the extent of elements as well as losses of material. The application of the the damage in order to produce a result comparable to that of six approaches shows three different levels of damage the previous approach. The new approach (Del Soldato et al. classification for this structure. The differences can be 2017) that combines all previous methods allows the analysis explained considering the parameters considered by the to be performed in more detail, including the extension of the various authors. According to Alexander (1986)and damage and the frequency and the opening of the cracks. The Chiocchio et al. (1997), the grade of damage is evaluated as evaluation of the damage allows for an assessment of the Moderate. Chiocchio et al. (1997) consider centimeters as the entire level of damage for the entire building. This approach unit to describe the opening of the cracks and include severe Fig. 12 Damage assessment for two buildings located in the study area by means of different approaches: a) three-level con- crete structure located close to the landslide crown; b) two-level masonry building positioned on the left flank of the landslide. Both edifices were classified ac- cording to the (1) Burland et al. (1977), (2) Alexander (1986), (3) Chiocchio et al. (1997), (4) Cooper (2008), (5) Baggio et al. (2009), and (6) Del Soldato et al. (2017) approaches. Damage are highlighted by red arrows, and open joints between the nearby structures are shown in blue Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) damage in the intermediate class. Similarly, Alexander’sclas- surveyor cannot enter private property, and he/she can assess sification (1986) considers cracks that affect structural the damage only from the outside, considering obstacles due elements and distortion angles to belong to the Moderate to vegetation or gates. This consideration is important during class. The approaches described by Burland (1977)and the application of damage classifications to correctly assess Cooper et al. (2008) categorize the recorded damage to struc- their severity, although several of the schemes consider the tures in terms of the width and number of cracks more severe- internal conditions of walls and the degree of pavement incli- ly than the two previously mentioned schemes, and the inves- nation. These data are particularity difficult to analyze during tigated building falls into the Severe rank. The classifications preliminary field campaigns or surveys that examine a great proposed by the DPC (Baggio et al. 2009) and Del Soldato et number of buildings, except for emergency interventions in al. (2017) are the only two that classified the building as Very restricted areas. Several factors, such as permission to access severe. The severity and conservative results from these two private properties, fenced areas, and damage hidden by vege- approaches could be justified by their original aim to provide tation, have to be considered during the interpretation of build- quick assessments of fitness for human habitation. In addition, ing damage maps. The restriction of access to the structure to they are unique in that they consider the extension of the better investigate the damage situation could be considered a damage with respect to the entire structure combined with strong limitation of the approach since access to private prop- severity. The entity of the damage is confirmed by the conser- erties is usually only permitted in case of emergency. vation status of the structure, which was abandoned for several Information regarding the crack pattern that affects the internal years. portion of the structures can improve the damage classifica- For some structures, it should be possible to make a com- tions and, if available, they must be implemented for a better parison between previous and future surveys (e.g., see Fig. 10) evaluation of the damage. in order to detect the evolution of the damage and the struc- The evaluation of the damage extent used in the DPC ap- tural conditions through time. Monitoring of the widening of proach (Baggio et al. 2009), despite its apparent lack of sim- cracks and damage to the facilities is also useful for ensuring plicity in overcoming the abovementioned difficulties, was the safety of residents as well as for understanding the tempo- demonstrated to be a powerful improvement to better evaluate ral evolution of the landslide and reducing the possible occur- structures that were differently affected by the damage. rence of additional damage. Furthermore, the contribution of Cooper’s methodology The Cooper (2008) and Del Soldato et al. (2017)ap- (2008), which also allows assessment of the landslide ground proaches also take facilities, such as walls and sidewalk, in damage, is an important element for providing better descrip- addition to the edifices, into consideration in the classification tions of the landslide-induced damage that affects an area. approach. In this work, structures and infrastructure were con- All of the benefits and constraints of the five critical ana- sidered using all methods, and it is very interesting to note that lyzed classifications highlighted above should be used to cre- elements different from the edifices were categorized as the ate a new categorization. A novel approach (Del Soldato et al. highest damage levels (Very severe or Partial collapse). The 2017) was recently published according to the results of the results of investigating further elements with respect to the applications of the literature methods in different sites; it edifices, such as sidewalks, ground fractures and walls, are maintained a division into two parts of the structure in order important for better delineating the extension of territory in- to consider the extent of the damage, the width of the cracks in volved in instabilities, mainly in rural areas as those investi- millimeters and the a posteriori classification of affected build- gated in this work. ings. The application of the new approach is more focused on All of the applied methods revealed some benefits and the identification and categorization of the severity of the constraints. For example, the use of millimeters as a unit for damage that affects the structures, in addition to its extent, measuring the widening of cracks (Baggio et al. 2009; considering the difficulties of access to private dwellings dur- Burland 1977;Cooper 2008) was found to be better than the ing the survey. use of centimeters (Alexander 1986; Chiocchio et al. 1997). The graduation of the damage severity beyond preliminary The evaluation of cracks affecting the foundations (Alexander damage assessments based on external features, can be used 1986), where possible, was found to be useful, even if very for different purposes to improve the understanding of study rarely applicable. Almost all of the methods, except those sites if combined with other information (Infante et al. 2016). described by Cooper (2008) and Del Soldato et al. (2017), Starting with the building and facility categorization, some do not consider the importance of the external visibility of preventive measures can be improved to avoid the occurrence the damage in their descriptions. Notably, all of the conducted of further damage in inventoried landslide-prone areas. In field campaigns allowed surveying the damage recognizable areas where possible landslide-induced damages have been from the outsides of the structures; almost all the surveyed recognized, the development of inventory maps and suscepti- structures are abandoned or access was denied by the owners. bility maps should be considered to improve the knowledge of This is a highly relevant issue because, in most cases, the the region and to support future planning decisions (Lee et al. M. Del Soldato et al. 2003; Di Martire et al. 2012; Guillard and Zezere 2012; approaches were devised to categorize the level of damage Righini et al. 2012; Bianchini et al. 2016). Furthermore, it that affects buildings, and despite a similar description of the could be a fundamental support for state legal procedures to damage, the involvement of various parameters allows differ- assess and reduce the risk of landslides and to increase the ences in the building classifications. resilience of infrastructure through more efficient design. The differences observed in the resulting maps were Some examples include updating urban development plans discussed based on the characteristics of the approaches as and the obligation to perform geotechnical investigations, in- well as the locations and the features of the buildings in- cluding stability analysis, in areas close to buildings damaged volved. The most complete and appropriate method for the by landslides. In the end, to prevent increasing economic area of interest was put into practice, even if a better solution losses, some reinforcing measures based on the effects suf- might have been to merge different features of existing ap- fered by the structures close to undamaged buildings, e.g., proaches to homogenize the procedure and to avoid some by means of underpinning, should be considered if the struc- drawbacks. The difference in classification of structures and tures are located in areas susceptible to landslides. Notably, infrastructure, as well as in ground fractures for the two more the area of study is principally rural, and the number of struc- recent approaches, depended on the different parameters used tures and infrastructure is low. The same comparison of dif- in the classifications once the data were collected. Several ferent methods conducted in an urbanized area could be more considerations that involved the identification of the cracks, consistent, but it has to be considered that the majority of the possibility of surveying the damage in private dwellings, landslides affect low-urban areas. For this reason, the resulting and the main information that has to be recorded to achieve classification appears to be partially mottled in some cases, good and reliable building classifications, were also discussed whereas for built up areas, the higher number of analyzed in order to extract the limitations and the strengths of each structures exhibit a more homogenous classification. This is method. confirmed by comparing the upper portion of the landslide, To summarize, the best method for describing the where several contractions are present, to the other two damage level and the real situation of the structures exanimated sectors with sparse structures. However, the as- seems to be the recent method developed according to sessment of damage is independent of the number of the con- the drawbacks and the benefits of each applied approach. structions investigated inasmuch any applied method was The strength of this approach resulted in the ability to comparative, but all of the approaches were based on the rec- investigate the severity of the cracks, considering several ognition and analysis of the fractures affecting an edifice. features of previous methods, combined with the exten- Corrective measures to restore damaged buildings or to sion of the damage and the categorization of the ground intervene in the activity and the continued evolution of the fractures that can help define the area involved in the phenomenon. This classification offers a simpler assess- mass movement are difficult to suggest on the basis of structural damage classifications alone. To pursue these ment of cracks to be carried out during field surveys goals, specific structural analyses must be performed, and based on observable and clear signs as well as taking the improvement described by Cooper (2008) and slightly into account reference widths and an a posteriori classi- modified by Del Soldato et al. (2017), which involves catego- fication of the structures by considering the effects of the rizing ground surface fractures, in addition to hydrogeological ruptures. and geomorphological studies, can help to select which mea- Ultimately, some considerations of the importance and the sures to adopt and to design better measures after landslides usefulness of the building damage data were performed. The are reactivated. information that can be extracted from the resulting maps can assist in managing and planning prevention and remedial ac- tions implemented in different phases and to avoid possible Conclusions casualties. Some examples include implementing structural and non-structural preventive measures in susceptible areas, Six existing classification methods for landslide-induced dam- monitoring landslide affected areas, providing support to local age were presented, compared, and applied to the structures administrators for planning and promulgating legislative re- and infrastructure within and close to the Colle Lapponi-Piano strictions, and helping private and local authorities renovate Ovetta landslide, in the municipality of Agnone (Molise re- damaged structures or evaluate the possibility of moving some gion, southern Italy). A total number of 30 buildings, two structures and facilities. walls, three concrete emplacements, and one electrical mast were investigated in order to classify the severity of damage Acknowledgements The authors thank the University of Florence for and to investigate the main benefits and drawbacks of each funding Dr. Matteo Del Soldato during a PhD research period in the Department of Civil Engineering at the University of Alicante. The au- method by a comparison of the resulting classifications to thors also thank the Spanish Ministry of Economy, Industry and evaluate their effectiveness in damage assessment. All of the Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Competitiveness (MINECO), the State Agency of Research (AEI) and the Cruden DM, Varnes DJ (1996) Landslides: investigation and mitigation. European Funds for Regional Development (FEDER) under projects Chapt 3. Landslide types and processes transportation research TEC2017-85244-C2-1-P and TIN2014-55413-C2-2-P and the Spanish board special report, p 247 Ministry of Education, Culture and Sport under project PRX17/00439. Del Soldato M, Bianchini S, Calcaterra D, De Vita P, Di Martire D, Tomás R, Casagli N (2017) A new approach for landslide-induced damage Open Access This article is distributed under the terms of the Creative assessment. Geomatics Nat Hazards Risk:1–14 Commons Attribution 4.0 International License (http:// Di Martire D, De Rosa M, Pesce V, Santangelo MA, Calcaterra D (2012) creativecommons.org/licenses/by/4.0/), which permits unrestricted use, Landslide hazard and land management in high-density urban areas distribution, and reproduction in any medium, provided you give appro- of Campania region, Italy. Nat Hazards Earth Syst Sci 12(4):905– priate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 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Landslides: investigation and mitigation. Transportation Research Seismol Soc Am 21(4):277–283 Board Special Report 247:12-35. National Academy Press, Wu C, Qiao J (2009) Relationship between landslides and lithology in the Washington, DC Three Gorges Reservoir area based on GIS and information value Schuster RL, Highland L (2001) Socioeconomic and environmental im- model. Front Forest Chin 4:165–170 pacts of landslides in the western hemisphere. US Department of the Wu X, Chen X, Zhan FB, Hong S (2015) Global research trends in Interior, US Geological Survey, Denver (CO) landslides during 1991–2014: a bibliometric analysis. Landslides Schuster RL, Fleming RW (1986) Economic losses and fatalities due to 12:1215–1226. https://doi.org/10.1007/s10346-015-0624-z landslides. Bull Assoc Eng Geol 23(1):11–28 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bulletin of Engineering Geology and the Environment Springer Journals

Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy)

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Earth Sciences; Geotechnical Engineering & Applied Earth Sciences; Geoengineering, Foundations, Hydraulics; Geoecology/Natural Processes; Nature Conservation
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Abstract

Landslides are among the most important and frequent natural calamities that cause severe socio-economic and human losses. After earthquakes, landslides are responsible for the greatest number of casualties and the largest amount of damage to man-made structures. On average, southern Italy is affected by a high spatial density of landslides due to its complex geological setting, which often predisposes it to slope instability phenomena under both natural and anthropogenic influences. Structurally complex formations are widespread in the southern Apennines and are characterized by high heterogeneity and very poor mechanical properties. Thus, these formations represent one of the main factors contributing to the predisposition of slopes to landsliding. In this paper, landslide-induced damage was investigated and analyzed in an area within the municipality of Agnone (Molise region), which is affected by a complex landslide that involves a structurally complex formation. The approaches used were based on six different methods that have previously been described in the literature, and a comparison of the results was made. Data regarding the damage, which consists largely of cracks observed in buildings and at the ground, were compiled through field surveys. The results were critically analyzed to note the advantages and constraints of each classification scheme. The aim of the work was to apply and compare different approaches in order to test the best and most accurate procedures for assessing damage due to landslides at the scale of individual buildings as well as to provide an objective assessment of the degree of landslide damage to structures and facilities. . . . . Keywords Landslides Structurally complex formations Damage classification Buildings Agnone Introduction hazard worldwide (Schuster 1996; Schuster and Highland 2001). They have potentially catastrophic effects and cause Landslides are gravity-controlled natural or anthropogenic considerable socio-economic damage as well as fatalities. processes that represent the most widespread geological Mass movements are caused by several predisposing and * Matteo Del Soldato Nicola Casagli matteo.delsoldato@unifi.it nicola.casagli@unifi.it Domenico Calcaterra Diego Di Martire domenico.calcaterra@unina.it diego.dimartire@unina.it Earth Sciences Department, University of Florence, Via La Pira 4, Silvia Bianchini 50121 Florence, Italy silvia.bianchini@unifi.it Department of Earth Sciences, Environment and Resources, Roberto Tomás University of Naples Federico II, Largo San Marcellino 10, roberto.tomas@ua.es 80138 Naples, Italy Pantaleone De Vita Departamento de Ingeniería Civil, University of Alicante, P.O. Box pantaleona.devita@unina.it 99, E-03080 Alicante, Spain Massimo Ramondini Department of Civil, Architectural and Environmental Engineering, massimo.ramondini@unina.it Federico II University of Naples, via Claudio 21, 80125 Naples, Italy M. Del Soldato et al. driving factors, including both natural and anthropogenic fac- The level of damage was assessed by means of different tors, such as deforestation or poor urban planning. existing methods developed in various contexts and for Anthropogenic factors are locally worse than natural ones different purposes. (i) The first method is based on the (Wu and Qiao 2009; Di Martire et al. 2012;Tofani etal. rehabilitation of the observable cracks (Burland 1977; 2013;Wuetal. 2015). Boscardin and Cording 1989); (ii) the second method was In Italy, population growth and the consequent expansion developed after an important landslide event in Italy of urban areas (Rybár 1997) have often induced people to (Alexander 1986); (iii) the third is focused on the survey build structures in areas over dormant landslides or at the of damage to buildings in landslide-affected areas edges of active landslide areas. Moreover, the disregard of (Chiocchio et al. 1997); (iv) the fourth approach is a the laws countervailed with several successive amnesties be- scheme realized by merging several damage classifications cause of infringement, in addition to the loss of memory of for use with subsidence, mining-related, and landslip past ruinous landslide events, have led to the development of events (Cooper 2008); (v) the fifth method (Baggio et al. facilities in hazardous areas, such as volcanic- or landslide- 2009) was proposed for post-seismic events by the Italian prone regions. Urban expansion can cause modifications to Department of Civil Protection (DPC hereafter); and (vi) hillslope morphology, inducing terrain remobilization and re- the sixth method is a recently published approach based on activation of old landslides that were previously dormant or the previous ones and was developed in two subsequent suspended, despite thousands of years of knowledge of nega- phases to assess the severity of cracks and constructions tive experiences (Chiocchio et al. 1997). (Del Soldato et al. 2017). Landslide-induced damages at Physical vulnerability, which defines the level of damage to the study site were recorded and assessed by means of critical infrastructures and buildings, is a key parameter in risk two field surveys conducted in November 2015 and in assessment. The occurrence of several landslides in urban July 2016. areas has highlighted the need to create a standard procedure The main aim of this work is to apply and compare to recognize and classify different levels of damage in order to different methods for classifying landslide-induced dam- help land management authorities (Alexander 1986)to focus age on structures and facilities in order to evaluate the and carry out mitigation strategies. Slope movements cause most accurate field procedure for the management and damage to buildings and other facilities and impose direct adoption of prevention and remedial measures through (e.g., replacement, repair or maintenance of damaged struc- a landslide case study in Agnone, Italy. The main advan- tures) and indirect costs (all other costs, which are difficult to tages and drawbacks of the different classifications are evaluate, e.g., losses of service) (Schuster and Fleming 1986; analyzed and discussed. Schuster 1996;Godtet al. 2000). These costs depend on sev- The paper is structured as follows: the next section briefly eral factors, including the dimensions and velocity of the mass describes the geological and geomorphological setting of the movement, the magnitude and type of the landslide mecha- Colle Lapponi - Piano Ovetta (CL-PO) landslide-prone area. nism, the lithology involved, the morphological features, and The presentation details of the different damage assessment the effects of anthropogenic activity. approaches applied for the categorization of the buildings and Attention is usually paid to planning strategies to prevent or infrastructures are given after that. Then the details of the field reduce urban landslide disasters, rather than evaluating their work developed for the classification of the damage and the impacts and the resulting damage. Maps illustrating the level recognized landslide-induced damage are described. of damage to affected buildings could provide an instrument Followed by a discussion of the main results obtained by to prevent the construction of facilities in historically applying the six methods. Finally, the main conclusions of landslide-prone areas. Furthermore, mountainous and geolog- the paper are summarized. ically complex environments characterized by the presence of structurally complex formations (Esu 1977), such as the southern Apennines, and associated with intense or prolonged Geological and geomorphological setting rainfall events, or to strong seismic shocks, are usually very prone to landslides. The study area (Fig. 1a) is sited in the western part of the This work addresses the description and classification municipality of Agnone (Molise, southern Italy) and is strong- of buildings and facilities damaged by the reactivation of ly affected by landslides and erosional processes. The CL-PO a slow-moving and intermittent landslide, known from the area is located in the catchment of the San Nicola Valley, a beginning of the XIX century, using six different damage sub-basin on the hydrographic right side of the Verrino assessment approaches. The landslide is located in the Torrent. municipality of Agnone (Molise region, southern Italy), The outcropping geological units include the Upper occurred in 2003, and involves Miocene-Pliocene clay- Miocene Agnone flysch (Sannitico-Molisane Formations) ey-marl lithologies. (Vezzani et al. 2004,Fig. 1b). This is characterized by Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 1 Location of the area of interest (a). Geological sketch map of the region of Molise (Vezzani et al. 2004) (b). The red line is the outline of the CL-PO landslide turbiditic siliciclastic deposits composed of alternating thin geotechnical campaigns in which four boreholes were drilled. layers of clayey sandstones, sandstones, and arenites They recognized four distinct layers (Fig. 2), described from (Filocamo et al. 2015). The CL-PO landslide involves the top to bottom as follows: upper member of the Agnone flysch, which is made up of marl, clayey, and subordinate grayish sandy levels with Level A – hard rock and mudstone fragments distributed low mechanical resistance and some alterations. Some throughout a chaotic and plastic clay matrix. Direct shear tests lithic intercalations, consisting of sandstone or calcare- performed on matrix samples indicated a peak friction angle ous levels with highly variable thicknesses, are also of approximately 19° and a cohesion of 20 kPa. This horizon present. The Agnone Formation is covered by a super- was directly involved in the 2003 reactivation of the CL-PO ficial regolith horizon composed of clay, silty clay, and landslide; occasional sand with diffuse alteration traces, abundant Level B – gray clay, silty clay, sandy clay, and silty sand. organic material, and some clasts. This layer displays medium plasticity and has a drained peak Calcaterra et al. (2008) performed a geotechnical charac- friction angle near 23° and a drained cohesion of approximate- terization of the landslide by means of several geological and ly 28 kPa; M. Del Soldato et al. Fig. 2 Engineering geological cross section passing through the median axis of the landslide with the locations of boreholes S1, S2, S3, and S4 modified from Calcaterra et al. (2008). A – hard rock fragments and clays; B – clays and sands; C – limestone level; D – marls and clays Level C – calcareous levels with thicknesses varying from The climate of the region is temperate with temperatures 0.1 to 1.0 m; ranging from 0 to 27 °C in winter and summer, respectively. Level D – marly clays, marls, and clayey marls with silt and Precipitation falls primarily during the rainy period from clay fractions. This horizon exhibits a plasticity comparable to September to April with an average monthly accumulation that of level B but with a drained peak friction angle close to approximately of 80 mm to which the snow must be added. 22° and a drained cohesion of approximately 60 kPa. During the summer season (from July to August) the accumu- lated rainfall is approximately 45 mm (http://www.regione. The main sliding surface is located at a depth of approxi- molise.it/schemiidrici). The morphology of the area has mately 25 m in the upper and central part of the landslide. The changed constantly over time as the reshaping of the earth depth of the surface of rupture considerably decreases in the surface has progressed due to the evolutionary stages of the lower portion of the landslide, in which the movement seems landslide (Fig. 3). After the reactivation occurred in 2003, an to evolve into an earth flow up to a few meters thick. important standing water body was identified in the middle Weathering effects, which consist of discolored, decomposed, portion of the landslide. This area is delimited by an important and weakened hard rocks, as well as scaly structures, were scarp and a counterslope, upstream and downstream, recognized in the borehole logs. An intercalation of fractured respectively, due to the geometry of the mass movement. and highly permeable calcareous beds, with thicknesses rang- The morphology of the area is flatter due to drainage works ing from decimeters to one meter, were observed (Calcaterra and the deposition of sediments transported by the surface et al. 2008). runoff. Other scarps that have been smoothed by erosional The ground morphology is controlled by the outcropping processes are clearly recognizable within the landslide area. lithotypes. Calcareous slopes show the highest gradients These scarps are located close to both flanks, as well as in the (close to 30–35°), whereas the argillaceous flysch units exhib- central and upper portion of the body of the mass movement. it slope gradients of approximately 5–10°. In areas where ero- The recognizable ground surface fractures were considered in sional processes are more significant, the steepness increases the classification as a relevant element for analysis of the to 15–20°. The 2003 CL-PO landslide developed along a extension and evolution of the gravitational phenomenon. slope sector that lies between 850 and 650 m a.s.l. and has a length of approximately 1500 m down to the confluence with Overview of the landslide inventory at Agnone the Verrino Torrent at 590 m a.s.l. The entire landslide area has an average slope of approximately 10° with peak values in the The availability of historical data, including information re- upper portion reaching 30°. garding localization and triggering factors, allows the Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 3 Decadal evolution of the CL-PO landslide. a) Mid-1990s, b) 2003, c) 2004, d) 2005, e) 2007, f) 2015 formulation of future realistic scenarios concerning the evolu- Reactivation of the CL-PO landslide tion of the slope instability (e.g., Calcaterra and Parise 2001; Calcaterra et al. 2003) and the detection of potential After an intense rainfall event that affected southern Italy be- reactivations and impacts of the phenomenon. tween the 23rd and the 27th of January 2003, with more than Landslides have been known in the municipality of 200 mm of rain falling over 72 h, the investigated area was Agnone since at least the beginning of the twentieth involved in an important reactivation of a dormant historic century. The oldest report describing an instability event landslide due to an unusual increase in pore pressure refers to a phenomenon that occurred in March 1905 in (Calcaterra et al. 2008). In the municipality of Agnone, a cu- the San Nicola Valley due to the combination of a pe- mulative precipitation of approximately 50 mm was measured riod of intense rainfall and snowmelt (Calcaterra et al. in the meteorological station located in CL-PO (Lat 41.80° 2008,Fig. 4a). This event damaged the bridge that car- and Long 14.33°) belonging to Regional Agency for the ried the main access road to the historical center of Agricultural, Rural and Fishing Development (Agenzia Agnone (Almagià 1910). Regionale per lo Sviluppo Agricolo Rurale e della Pesca - The municipality of Agnone has been successively ARSARP - www.arsarp.it/agromtorologia)inthe same affected by several small and large landslide events. period in which a reactivation of the landslide (Calcaterra et Archival and bibliographical landslide research, reported al. 2008), with a complex style consisting of a succession of in the nationwide AVI Project (Guzzetti et al. 1994), large roto-translational slides by an earth-flow (Cruden and revealed more than 60 landslides that occurred in the Varnes 1996). The event involved several facilities, forcing municipality of Agnone and the surrounding territory the municipality’s administration to adopt restrictive mea- from 1970 to 1998. In February 1984, a mass move- sures, i.e., the evacuation of 13 buildings located in the area ment occurred close to the study area that affected two involved in the landslide, in which 17 families were living. pillars of the viaduct of a State Road (Guadagno et al. The municipal administration, owing to the severity of the 1987), forcing the demolition of a section of it (Fig. situation, earmarked funds to perform several urgent interven- 4b). In 1994, a mass movement affected the Colle- tions, such as the re-shaping of the area affected by the mass Lapponi area, causing the interruption of a dirt road. movement and the excavation of a trench in the upper part of Finally, the latest landslide inventory of the municipality of the body of the landslide in order to intercept and drain the Agnone was conducted by the IFFI Project (Italian Landslides water table, which locally reached the ground surface. Inventory Project) by ISPRA (Istituto Superiore per la During the years following the main reactivation, despite Protezione e la Ricerca Ambientale)in2008. the adoption of the abovementioned remedial measures, the M. Del Soldato et al. Fig. 4 Excerpt of the map published by Almagià (1910). The red box indicates the location of the CL-PO landslide (speckled in the figure); b) demolition of the State Road viaduct following the 1984 landslide (from Guadagno et al. 1994) entire landslide remained active, increasing its dimensions and topographic measurements were conducted using GPS equip- causing additional damage to facilities and buildings. During ment to evaluate the progressive evolution of the landslide and March 2004 and in the period between December 2004 and the enlargement of the main scarp. These data confirmed the January 2005, the landslide was reactivated by a series of effectiveness of the stabilization works in the central and low- heavy rainfall events (Fig. 5), increasing the area involved er sectors of the landslide, but not in the upper area. 6 3 and mobilizing an estimated total volume of 3.5 × 10 m Furthermore, in 2012, eight corner reflectors were installed (Calcaterra et al. 2008). on the mass movement to monitor the landslide (Di Martire Continued advancement of the movement that resulted in et al. 2013) by means of Differential Interferometric Synthetic progression of the landslide foot over approximately 70 m was Aperture Radar (DInSAR) techniques. recognized by June 2006, and a lower displacement rate was In November 2015 and July 2016, additional field surveys detected between April 2006 and April 2007. These observa- permitted the examination of the further evolution of the slope tions led to the adoption of new mitigation measures in the movement and the identification of a new boundary of the middle part of the mass movement, where ground subsidence landslide (red line in Fig. 6) as well as many tension cracks and the collection of surface runoff formed a landslide lake. inside and outside the landslide boundaries. The field cam- Consequently, additional reshaping of the slope and the exca- paigns were mainly devoted to identify, record, and assess vation of 10 trench drains (6.5 m deep and approximately the severity of the landslide-induced damage on several facil- 150 m long) were performed. These actions stabilized the ities located within and close to the landslide. middle to lower parts of the mass movement. From 2004 onward, a set of topographic benchmarks were placed within the unstable areas to monitor the surficial movement of the Methodologies for damage assessment landslide. From 2004 to 2011, the landslide advanced approx- imately 350 m at the toe and retrogressed approximately Displacements that occur in landslide areas are often revealed 270 m in the head sector, increasing the total length to as fractures on the ground surface or as ruptures and cracks in 1500 m (Fig. 6). In 2010 and 2013, two campaigns of man-made facilities. These effects appear when ground Fig. 5 Daily (blue bars) and cumulative (green line) rainfall from (a) December 2002 to January 2003 and (b) from December 2004 to January 2005. The red box highlights the rain event, which caused the main reactivation of the landslide (www.arsarp.it/agromtorologia) Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 6 Evolution of the boundaries of the CL-PO landslide from 2004 to 2011. Ground evidence recognized during the 2015 survey is drawn in red movements that affect the buildings are greater than the tensile The scientific community has developed some specific stresses that the structures are capable of accommodating classifications of damage for areas affected by natural cata- without apparent deformation. The first elements to reveal strophic phenomena, such as earthquakes (e.g., Wood and damage are the most rigid ones, such as walls and façades, Neumann 1931;Medvedev 1965; Grünthal 1998), subsidence or the weakest elements, such as joints (Bru et al. 2013). (e.g., Van Rooy 1989; Howard Humphreys & Partners, 1993; Building damage is commonly assigned to three general cat- Freeman et al. 1994), and landslides (e.g., Burland 1977; egories: architectural, functional, and structural damage. Alexander 1986; Geomorphological Services LTD, 1991; These categories were first disseminated by Skempton and Lee and Moore 1991; Chiocchio et al. 1997;Iovineand MacDonald (1956), who did not define clear boundaries be- Parise 2002). tween them. Architectural damage refers to the appearance of In this work, six different methods were used for classify- a structure (e.g., fine cracks in finishes, floor or panel walls, ing the observed damage to the facilities affected by the CL- cracks wider than 0.5 mm in plaster or wider than 1 mm in PO landslide. The methods include those of (a) Burland rough concrete and masonry walls). Functional damage af- (1977), slightly modified by Boscardin and Cording (1989), fects the use of the structure and produces extensive cracks, (b) Alexander (1986), (c) Chiocchio et al. (1997), (d) Cooper tilting of floors and walls, falling plaster, obstructed doors and (2008), (e) the DPC (Baggio et al. 2009), and (f) Del Soldato windows and other non-structural damage. Structural damage et al. (2017). The main characteristics and differences between reduces the stability of the structure manifesting as ruptures the different classifications are summarized in Table 1.The and distortions in support elements (e.g., pillars, columns and application of the six different methods of classifying the load-bearing walls). In practice, damage affecting facilities landslide-induced damage allows defining the most appropri- have to be assessed by performing field surveys, which are ate approach for this case study. This is useful for several highly conditioned by the criteria adopted and the experience purposes, such as civil protection management after signifi- of the operators. cant events, urban planning and managing of remedial and M. Del Soldato et al. Table 1 Main characteristics of the applied methods to classify the landslide-induced damage on structures (updated from Del Soldato et al. 2017) Burland et al. Alexander Chiocchio et al. Cooper DPCBaggio et al. Del Soldato et al. Year 1977 1986 1997 2008 2009 2017 Number of classes 6 8 8 8 4 8 Distinction of structure NO NO YES NO NO YES Reference values YES (mm) NO YES (cm) YES (mm) YES (mm) YES (mm) Partition of the structure NO NO NO NO YES YES Applicability on ground surface NO NO NO YES NO YES Note: ND means Bnot defined^ prevention measures, and architectural and engineering 1994;Iovine and Parise 2002). These include, for example, design. the type and age of construction of the buildings or the reno- vation works (Chiocchio et al. 1997). Burland 1977 Chiocchio et al. (1997) The simple approach presented by Burland (1977) was de- rived from the accumulated experience of the author in the Chiocchio et al. (1997) defined a new classification of land- field through three previous studies: i) a study of the economic slide damage to buildings that overcomes some of the draw- consequences on the heaving of construction on swelling clay, backs that were identified in the classification of Alexander by means of a simple classification of damage based on the (1986). The new approach was conceived thanks to an inter- ease of restoration (Jennings and Kerrich 1962); ii) a simple disciplinary effort involving geologists, geomorphologists, classification based on wide experiences in subsidence dam- and civil engineers. age (National Coal Board, 1975); and iii) a categorization This classification considers two different types of struc- structure-soil interaction proposed by the Coal Board’srecom- tures (i.e., masonry and reinforced concrete) and provides mendations (MacLeod and Littlejohn 1974). Burland’s(1977) quantitative reference values for some parameters. These im- classification is divided into six damage classes based on the provements were relevant to the analysis of the fractures to width of cracks and related to the ease of restoration. Within allow evaluation of similar cracks in different materials and to these classes, the widths of the cracks are approximate. minimize the subjectivity of the survey. The damage level was The measurement is related only to visible or esthetic dam- divided into eight different grades and, additionally, some age, observed corrosion, and cracks permitting the penetration general recommendations for rehabilitation measurements or the leakage of liquids or gases. For reinforced concrete, the were defined. The first three levels correspond to negligible adopted approach should be more severe (Nawy 1968). and weak damage; buildings affected by the fourth grade of damage exhibit some serious cracks, and restoration strategies Alexander (1986) are suggested for them; the fifth grade is characterized by several failures that affect the structure and the surrounding After an important landslide event occurred in Ancona, central area. The last class is assigned to buildings in which the level Italy, in 1982 an alternative intensity scale of damage was of damage is so severe that the extent of the damaged area has developed (Alexander 1983). This method referred to the to be accurately evaluated in order to decide whether to reno- landslide-induced damage observable on buildings and per- vate or relocate the entire construction (Chiocchio et al. 1997; mitted the comparison of the damage observed on different Iovine and Parise 2002). structures involved in the event. The proposed scale refers to landslide damage due to subsidence, rotational and transla- Cooper (2008) tional movements, and slow thrusts rather than to the impact of the avalanching debris (Alexander 1986). This approach The classification is formulated on the basis of several previ- includes eight damage levels based on the severity and wid- ous classifications for evaluating building damage caused by ening of cracks, the distortion of rigid elements and the degree subsidence and landslides. The affinity between several of settlement that affects the foundations in addition to two of existing schemes for recording damage caused by landslides which correspond to the most severe categories, i.e., partial and subsidence permitted the generation of a single scheme and total collapse of the structure, based on the cracks ob- that describes observable damage to buildings, independent of served on walls. However, some missing features of this meth- the causes (Cooper 2008). This classification also divides the od have been identified during applications (Crescenzi et al. severity of the damage into seven classes, from very slight to Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) total collapse, in addition to a class describing negligible dam- of this approach with respect to the previous approach is the age. The definition of the categories was based on studies by introduction of the extent of damage. the National Coal Board (Handbook 1975), Alexander (1986), For the aim of this work, only the two sections related to Geomorphological Service Ltd. (1991), Freeman et al. (1994), recording structural and non-structural damage were considered, the Institution of Structural Engineers (1994), and Chiocchio in addition to the introduction of the evaluation of the extension et al. (1997). of the cracks as affecting less than 1/3, a portion between 1/3 and In this classification, ground damage caused by landslides 2/3, or more than 2/3 of the building for each class of damage. and subsidence were included considering that most of the Accordingtothisapproach,the investigation of structures has to survey was performed by studying the external façades of be ideally divided in three parts considering intervals of 33% or buildings. In this approach, damage to roads and other facili- 67%. Additionally, the magnitude of the damage that affects ties can also be surveyed and could even be evaluated (Cooper each part of the structure can be assessed as null (D0), weak 2008). Cracks and fractures observed on facilities and the (D1), medium-severe (D2-D3), and very severe (D4-D5). The ground surface are related to more severe damage classes sum of the extent of the damage cannot exceed 1, representing (above the third grade). the entire building (e.g., 2/3 of D4-D5 + 1/3 of D2/D3). The damage grades are described by a scheme without The DPC classification was originally developed to evalu- details on cracks in foundations or other subsurface features, ate the fitness for human habitation of buildings after a seismic as Cooper (2008) considered that the recording of damage event. Therefore, for comparing the results obtained by this using more practical parameters has proven to be popular, approach to the others mentioned above, a further consider- simple, and easily performed in field surveys. ation was necessary to have the same number of classes. All possible combinations, considering the extent of the damage The Italian Department of the Civil Protection for each class and the four classes of cracks (D0, D1, D2-D3, approach (Baggio et al. 2009) D4-D5), were considered. Then, a conversion matrix was used to evaluate the seriousness of the damage affecting a single This method was conceived for surveying damage that affects unit according to the possible combinations of damage. For civil construction after seismic events in order to assess the each level of damage, a value was assigned and then grouped fitness for human habitation of the buildings. The applicability into eight classes varying from 0 (negligible damage) to 7 to landslide phenomena is derived from the causes of the (total collapse) in order to compare the resulting map with damage due to the effects of shear stresses in both cases. the other described classifications. This method was applied in several field situations involving seismic events in Italy (e.g., 1980 Irpinia earthquake in Del Soldato et al. (2017) Campania, the Abruzzo region in 1984, and the Basilicata region in 1990) and it was tested in subsequent earthquakes This classification was developed through the application and (e.g., the Umbria-Marche regions in 1997, and Pollino and the analysis of results of previous approaches to provide a rapid Basilicata-Calabria regions in 1998) with the view to enable evaluation of cracks and fractures during field surveys and a making judgements on the ability of structures to host their subsequent assessment of the buildings damage caused by inhabitants safely, so it does not address protection of the landslides. To create this new classification method, several structures. landslide-induced categorizations of damage to buildings This approach was devised to perform initial classifications were considered (Burland 1977; Alexander 1986; Chiocchio of damage magnitudes by means of quick surveys. It was et al. 1997;Cooper 2008) jointly with the approach for the conceived to assess the reliability of structures. Therefore, assessment of seismic event effects developed by the DPC the recording scheme for the damage is more complete than (Baggio et al. 2009) to insert the importance of the extension the one presented previously. It is composed of several tables of the cracks and fractures in the damage evaluation. suitable for emergency post-seismic event surveys. Overall, Furthermore, similar to the Cooper (2008) approach, external this recording scheme is composed of nine sections: a) three recognition plays a key role, and the ground fractures are also tables devoted to the identification and description of the ex- considered. Ground cracks are not considered related to the amined buildings; b) two sections referred to a quick assess- constructions, but singularly, in order to implement the knowl- ments of structural and non-structural damage; c) a section edge regarding severity and extension of the landslide effects. dedicated to evaluating the possible involvement of surround- The classification is divided into six ranks from no damage to ing structures in case of the collapse of edifices; d) a section very severe. In this categorization, the collapse is not consid- that addresses the geomorphological condition of the terrain ered because in the first phase the focus is the network of surrounding of the buildings; e) a section to assess the build- cracks and fractures that affect the structures. Subsequently, ing’s conformity with standards; and f) a final section to in- the extent of the damage has to be considered and, by means clude notable and useful information. The main contribution of a matrix, the entire building could be classified into eight M. Del Soldato et al. classes from Bno damage^, meaning safe construction, to These types of fractures on roads and ground surfaces Bunusable^, indicating an uninhabitable building. (Fig. 10) are investigated and classified only by the most recent approaches proposed by Cooper (2008)and Del Soldato et al. (2017). The identification and survey of these Description and classification of damage fractures, the assessment of their severity, and the investiga- tion of their probable correlation to the activity of the land- The January 2003 landslide reactivation was the most recent slide, can be important parameters to support the identification event that caused serious damage to facilities and buildings in of extension of the landslide-prone area. Agnone. Damages were chiefly related to the loss of support to An example can be made taking into account a sidewalk structures due to the downward and outward movements of the made of reinforced concrete (Fig. 10) that is located in the foundation zones (Hunt 2005). This effect was important for present crown of the landslide that currently shows an impor- forcing the administration of the local municipality to take some tant open crack pattern with detachment of a portion restrictive measures, such as a precautionary evacuation of sev- (Fig. 10b). In recent years, the crown of the landslide has eral houses located close to the area that were affected by the retrogressed, widening its boundaries and increasing its di- slope movement. In November 2015 and July 2016, forensic mensions, as reflected in the opening of new tension cracks analyses were conducted for 30 buildings, two walls, and three and the collapse of a part of the sidewalk bordering a building concrete surfaces near the landslide; one electric tower close to that does not show severe damage to the external façades. its left flank; and several tension and shear cracks on ground The in situ analyses provided qualitative and quantitative surface and pavements. For this purpose, external damages were information about the fractures used for damage assessment of surveyed using a regular scheme (see supplementary material by the studied elements, according to the six classifications de- Del Soldato et al. 2017) in order to collect as much information scribed earlier (Table 2 and Fig. 11), one for each methodol- as possible: i) date and site of the survey, hamlet, municipality, ogy applied to record the damage to the facilities located with- and province; ii) identification number of the structure under in the landslide-prone areas. It is worth noting that, although investigation; iii) coordinates of the façades; iv) type of con- these methodologies were originally proposed for the identi- struction, e.g., buildings, gymnasium; v) load-bearing materials, fication of damage to buildings, in this work they were also e.g., masonry or concrete; vi) date of construction and number of applied to categorize other man-made elements (i.e., an elec- floors of the edifice; vii) position with respect to the landslide; tricity mast, two walls, and three concrete areas) that were viii) draft and classification of the ruptures of on ground and strongly affected by ruptures. The results show that most of pavement; ix) drawing and categorization of cracks on build- the damage is located in areas where the landslide remains ings; x) extension of the damage in all structures or only in its active. Several structures, buildings and infrastructures, in portion; and xi) georeferenced photographs. The procedure for and close to the mass movement, therefore, within the land- collecting such information is considered important inasmuch slide prone-area, were investigated (Fig. 11a). that the same opening, or two similar cracks, in two structures built with different materials could have different meanings (Chiocchio et al. 1997; Iovine and Parise 2002). Results Different levels of damage that affect the buildings are grouped into several types: In this section, the results derived from the damage assessment of the building and the infrastructures placed in CL-PO land- & hairline cracks (Fig. 7a); slide by means of the different approaches described earlier & open fractures on external walls (Fig. 7b and c); are presented. & ruptures between walls and external pavements (Fig. 7d Following the classification of Burland (1977)(Fig. 11b), a and e); and large number of buildings (approximately 50%) present Slight & in rare cases, roof collapses (Fig. 7f). and Very severe damage, as several abandoned structures are strongly affected by damage and have partially collapsed. In concrete sidewalks and walls, the following elements Only two buildings have been assigned to the Negligible class, were investigated: and four fall into the Very slight class. Negligible damage were observed in more recent structures, in a small house that was – hairline cracks (Fig. 8a and the red arrow in 8c) and probably renovated in recent times and in buildings that were – open cracks (Fig. 8b–d). built further from the landslide than the others. The Very slight class includes a building located on the present-day crown of Cracks recognized on the ground (Fig. 9b) or on pavements the landslide. This rank is due to the low level of damage (Fig. 9a) were plotted on a topographic map and photographed present in its façades, although important damage could affect as well as spatially identified with a GPS tracker. its foundation. Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 7 Damage identified on buildings. a) Hairline crack in the plaster of and the pavement in a masonry building; e) open crack, more than a masonry wall; b) open crack, approximately 1.0–1.2 cm wide, in a wall 10 cm wide, between a wall and the ground surface of a reinforced of a reinforced concrete building; c) open crack, approximately 4 cm concrete building; f) collapsed roof in a masonry building wide, in a wall of a masonry building; d) open crack between a wall Alexander’s(1986)(Fig. 11c) classification measures existing high risk. Another noteworthy point is that this crack apertures in centimeters instead of millimeters. This methodology considers two categories for buildings that implies that the classification is less sensitive to damage, are strongly affected by damage: Partial collapse and Total and most of the facilities are grouped into the Light and Collapse. The nine buildings assigned to the Very severe class Moderate classes. Additionally, in this classification, using the Burland (1977) approach are divided into three clas- Bevacuation and rapid attention to ensure^ is recommended ses according to Alexander’s(1986) classification: three of the for those facilities that exhibit Moderate damage. Concerning buildings fall into the Very serious class, five fall into the the buildings located on the crown of the landslide, this meth- Partial collapse rack, and one falls into the Total collapse odology classifies the damage as Negligible, despite the category. Fig. 8 Damage recognized on concrete slabs and walls. a) Hairline crack in pavement; b) open rupture in a slab; c) hairline (red arrows) and open fractures in a concrete wall; d) damage to a masonry wall M. Del Soldato et al. Fig. 9 Cracks located close to the landslide on (a) the pavement of a road and (b) the ground surface. In photograph (b), a vertical slip is recognized The Chiocchio et al. (1997)(Fig. 11d) approach also mea- sensitivity in assessing damage that is caused by the use of sures cracks in walls using centimeters. However, this ap- the millimeter as the unit of measurement, and it is a more proach includes the construction distinction between masonry appropriate methodology for classifying ruptures that affect and reinforced concrete, in contrast to the previously men- some facilities, such as pillars, walls, and concrete sidewalks. tioned methodologies. In this way, structures affected to a The DPC approach (Baggio et al. 2009) divides the level of significant degree by rigid settlement, which were previously damage into four classes, although the classification includes assigned to the low damage classes, are grouped with those eight damage classes: two low levels (None and Negligible), affected by several cracks. A concentration of buildings is four categories representing significant damage (Severe, Very assigned to the Light and Moderate damage classes, and the severe, Partial,and Total collapse), and two intermediate authors suggest evacuation even for the Moderate category. grades (Slight and Moderate)(Fig. 11f). This approach pro- Moreover, it is important to note that using this categorization, vides a more evenly distributed classification of damage (thus the building (B01) located on the probable present-day crown most of the buildings are not ranked into only one or two of the landslide has few, narrow visible cracks in its external classes) than the previous described and applied approaches. façades, perhaps justifying the low damage classes assigned Despite the small number of facilities located in the study area, by the classification, despite an important rupture that affects an increasing number of structures are ranked into the catego- the front concrete sidewalk. Six buildings, probably aban- ries reflecting high levels of damage (Severe and Very severe). doned several years before the main event, are assigned to This methodology gives more attention to damaged buildings the highest categories of damage (i.e., Partial collapse and since it was conceived to evaluate the fitness for human hab- Total collapse), as in the Alexander (1986) approach. itation of structures after a damaging seismic event. The Del Soldato et al. (2017) categorization provides a In his approach, Cooper (2008)(Fig. 11e) introduces the description and categorization of landslide ground damage in homogeneous distribution of the structures located in the addition to the classification of the damage recognizable on landslide-prone area due to its simple but detailed approach facilities and buildings. This classification uses millimeters to that includes two phases. These two steps of damage measure the opening of the cracks that appear on the elements evaluation and subsequent structure assessment in sensu of the investigated structures. In our case study, the classifica- stricto allow a better discrimination of the severity of cracks tion assigns an important number of buildings to Class 3, and fractures. Similar to the Cooper (2008) approach, the in- compatible with the Moderate category of the other ap- vestigation takes into account the external portions of the proaches. Comparing the proposed classification with the oth- structures eliciting an increment in the low ranks of the build- er areas, more facilities are sorted into the higher levels of ings affected by weak fractures in external facades but rele- damage. This is probably due to the method’s higher vant fractures and displacement in the foundations. Several Fig. 10 Evolution between 2003 (left) and 2015 (right) of a rein- forced concrete perimeter side- walk of a building located on the crown of the landslide Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Table 2 Summary of the damage assessment in the different location of the study area ID Structure type Position respect Damage description Damage classification to the landslide Burland 1977 Alexander 1986 Chiocchio 1997 Cooper 2008 DPC 2009 Del Soldato 2017 B01 CS CR Sparse thin cracks in the facades; several 21 1 2 2 3 fractures between the walls and the sidewalk. B02 CS CR Rare thin cracks mainly starting from the 53 3 3 3 5 corner of the doors or windows. An important open rupture (up to 10 cm) affecting the foundation is visible on the south-eastern corner B03N MB CR Negligible cracks and one joint in the 01 1 1 1 2 connection area with the B03S B03S MB CR Some thin cracks around the doors and 22 2 2 3 3 windows and an open joint in the connection between this construction and the connected B03N B04N MB FL Several thin, open and filled cracks; one 34 4 4 5 5 important disjunction affecting a railing in bricks. Roof weakly bent and several cracks between the walls and the external sidewalk. Connected with the B04S B04S MB FL Some very important ruptures (up to 5 cm) 56 6 6 6 7 and roof collapsed. Connected with the B04N B05N MB FL Several open cracks (up to 2 cm) mainly in 53 3 5 5 6 the eastern façade and close to doors, windows and the terrace; very open joint between these buildings and the connected B05S B05S MB FL Some open cracks on column and starting 43 3 4 4 5 from doors and windows, roof weakly bent, very open joint in the connection area with B04N B06N MB CR Diffuse open cracks (up to 1 cm) in the south21 1 1 1 2 part of the east exposed façade, sparse thin cracks in the entire construction, important swelling in the retaining wall. B06S CS CR Diffuse very thin fracture affecting only the 43 3 4 4 5 plaster B07 CS CR No cracks and damage 0 0 0 0 0 1 B08E MB CR Important open joint (up to 3 cm) crossing an45 4 5 5 7 entire façade, other thin ruptures, partial collapse of a roof. Connected with the B08W and B08S without joints B08W MB CR Several open cracks (up to 1.5 cm) close to 34 3 4 4 5 the windows and door in one façade, in the other one only two ruptures (one open M. Del Soldato et al. Table 2 (continued) ID Structure type Position respect Damage description Damage classification to the landslide Burland 1977 Alexander 1986 Chiocchio 1997 Cooper 2008 DPC 2009 Del Soldato 2017 about 1 cm and one recently filled). Connected with the B08E and B08S without joints B08S MB/CS CR Few thin cracks starting from doors or 22 2 2 2 3 windows boundary. Connected with B08E and B08W without joints B09W MB CR Some vertical open cracks (up to 1 cm), 33 3 4 3 5 bending of the beam and little distortion of the north-east corner of the roof. Connected with B09E and B09S with thin joints B09E CS CR One vertical open crack (up to 1 cm), several24 3 3 3 4 thin ruptures close to doors and windows and in facades, some cracks between the walls and the external sidewalk. Connected with B09S and B09W with thin joints B09S MB CR Some vertical thin joint reflecting, probably, 32 2 3 2 5 several subsequently adding from the construction and close to doors or windows, roof slightly bent in a central region. Connected with B09E and B09W with thin joints B10 CS CR Very few hairline cracks in a façade affecting11 1 2 1 2 the plaster and in a corner between the external wall and the sidewalk B11N CR Some thin cracks between the external wall 12 1 1 1 3 and the sidewalk, rare fractures in the facades. Connected with B11O along an open joint B11O MB CR Diffuse thin cracks, some filled, close to the 23 2 3 3 4 doors and windows and between the external walls and the sidewalk. Connected with B11N along an open joint B12N MB FL Some thin crack around windows and tracing22 2 2 2 2 the line of the roof. Connected with B12N by a thin joint B12S MB FL Two fracture in the external stairs structure 12 2 2 2 3 and some think cracks close two windows. Connected with B12S by a thin joint B13m MB FL Rare hairline cracks affecting the facades. 22 2 3 2 2 Connected with B13S through thin and filled joints and with the B13N by open joints B13N MB FL Severe affected by cracks and open fractures35 5 5 5 7 vertically and close to the doors and Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Table 2 (continued) ID Structure type Position respect Damage description Damage classification to the landslide Burland 1977 Alexander 1986 Chiocchio 1997 Cooper 2008 DPC 2009 Del Soldato 2017 windows, open joint between the external walls and the sidewalk. Some of them are filled and signs of renovation are visible. Connected with the B13m by open and filled joints B13S MB FL Rare thin cracks on facades and filled ruptures12 2 2 2 3 between external wall and sidewalk. Connected with B13m through thin and filled joints B14 MB FL Almost totally collapsed (roof and floor) and57 7 7 7 8 wall twisted. B15E MB CR Partially collapsed (roof) and several cracks 34 4 5 5 8 on facades. Connected with the B15m by open joints. B15m MB CR Partially collapsed (roof) and several cracks 56 6 6 6 8 on facades. Connected with B15E and B15W by open joints B15W MB CR Partially collapsed (roof) and several cracks 56 6 6 6 7 on facades. Connected with the B15m by open joints B16 MB CR Diffuse open cracks (up to 1.5 cm) and roof 34 4 4 4 6 visible bent. E01 Steel FL Structure not affected by damage, but 23 3 4 4 6 foundation partially exposedbymeans of the boundary of the landslide S01 CS CR Diffuse thin cracks, some open rupture, partial56 6 7 7 7 region collapsed. Several cracking affecting the connection with the external wall of B01 S02 CS CR Diffuse very open cracks (up to 5 cm) and 56 6 7 7 6 filled ruptures S03 MB/CS FL Diffuse very open cracks (up to 5 cm) and 44 5 6 5 7 filled ruptures, tilting of parts of concrete andhole inthe surface W01 CS CR Several open cracks (up to 1 cm) and 43 3 5 4 6 horizontal and vertical distortion W02 MB CR Two main open cracks (up to 5 cm) and 55 5 7 6 6 horizontal and vertical distortion See location in Fig. 11 CS - reinforced concrete/steel; MB - masonry/bricks CR - crown; FK - flank - TO toe M. Del Soldato et al. Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Fig. 11 a) Localization of the investigated buildings and facilities with some families from their dwellings due to the serious damage their damage classifications according to b) Burland et al. (1977), c) that was caused to some structures. Despite the realization of Alexander (1986), d) Chiocchio et al. (1997), e) Cooper (2008), f) DPC relevant stabilization works in the landslide body, the follow- (Baggio et al. 2009), g) Del Soldato et al. (2017) ing years exhibited an enlargement of the dimensions of the landslide. The advancement of the toe and retrogression of the constructions are categorized in the low ranks of damage main scarp, with consequent involvement of the lateral flank (Negligible and Weak), and a relevant number is characterized to accommodate the movement, represents a threat of damage by important damage (Moderate and Severe). In the left flank to facilities and buildings located in the surrounding area. of the landslide (i.e., area 2), the constructions are categorized This paper focused on the comparison of six different with a high level of damage (Severe and Very severe)due to methods of landslide-induced damage classification for facil- the important displacement caused by a double component of ities and buildings located in a landslide-prone area, a funda- movement. The first displacement component affects the right mental parameter to prioritize further investigations. The clas- side of the study area that is under the influence of the CL-PO sification step can help local administrators decide where landslide. The second component is due to an enlargement of more detailed structural analyses should be performed or the mass movement that affects the neighboring basin. The where further actions must be considered. Furthermore, in three sidewalks and the two investigated walls are all catego- emergency cases, this preliminary structure classification rized into a high level of damage (Severe and Very severe)due may be sufficient to support the order of some restrictive mea- to the open cracks and fractures that affect them and, in one sures, the fulfillment of practice repairs or reinforcement of the case, the detachment of a portion of the sidewalk due to the main damaged structures. For this purpose, six assessments of regression of the landslide border. Only one edifice is featured landslide-induced damage approaches (Table 3)wereapplied by No damage due to its recent construction or renovation. and compared. The six classification methods, which seemed Three structures are classified as Total collapse: two of them, to be very different from each other, were found to have strong both abandoned, are close to the crown, whereas the third is similarities. In addition to a general comparison, two build- close to the left flank of the landslide. ings, one located upslope with respect to the crown of the CL- In addition to the structures, walls and sidewalks, an elec- PO landslide and the second on its left flank, were chosen to tricity mast located on the left boundary was investigated in analyze and discuss in detail the application of the features of order to assess its safety due to its important function for the the different methodologies for assessing landslide-induced surrounding edifices. This element is a steel rigid structure, damage. founded on a concrete sidewalk. The approaches proposed by The first building (Fig. 12a) is located on the present-day Burland (1977), Alexander (1986), and Chiocchio et al. crown of the landslide, as indicated by a significant ground fissure that cuts across under the entire structure. The displace- (1997) assign this facility to the medium level of damage, despite the displacement observed on the south-eastern side ment affects the building’s foundation and is easily recogniz- of its foundation. However, the DPC (Baggio et al. 2009), the able in the building’s southeastern corner (red circle in Cooper (2008), and the Del Soldato et al. (2017) methods Fig. 12a) by an evident opening with respect to the ground classify the damage to this facility as very severe. The stability up to 10 cm/year. The six applied approaches evaluate the conditions of the pillar base are characteristic of problems that damaged structures differently, depending on the element on affect structures located close to the landslide crown or flanks which they are focused. However, all of them assessed the (e.g., the two buildings located at the top of the landslide- damage level as Moderate, except the classification developed prone area). The lateral boundary of the landslide is located by Del Soldato et al. (2017). The method proposed by Burland under the electricity mast, as seen from the ground displace- (1977) does not consider ruptures involving building founda- ment on one side of the mast, whereas no signs of movement tions but only the cracks on the façades. In this case, aside are present on the other side. from the considerable ground fissures that threaten the foun- dations, no heavy relevant damage to the façades were sur- veyed. Alexander’s(1986) classification mainly considers the Discussion degree of settlement that affects structures instead of the wide cracks that may exist in the walls or structural elements, but Several landslides affect the municipality of Agnone (Molise given the complexity, the structure was assessed with the same region, southern Italy) according to the historical investiga- entity of damage. The method suggested by Chiocchio et al. tions and reconstructions described in the literature. In 2003, (1997) considers both the degree of settlement that affects the CL-PO area was affected by an important reactivation of structures and recognizable fractures on the façades. The low an old intermittent mass movement, attracting public attention level of damage to the external walls compensates for the because of the severe damage caused to surrounding buildings substantial and continuing displacement that affects the foun- dations of the building, reducing the severity of the and facilities. The local authorities were forced to evacuate M. Del Soldato et al. Table 3 Equivalence of the damage categories considered by the different classifications Burland, 1977 Alexander 1986 Chiocchio et al., 1997 Cooper 2008 DPC Baggio et al., 2009 Del Soldato et al., 2017 0 Negligible 0 None 0 0 0 None 0 None G0 No damage 1 Very slight 1 Negligible 1 Negligible 1 Negligible 1 Negligible G1 Negligible 2 Slight 2 Light 2 Light 2 Light 2 Light G2 Weak 3 Moderate 3 Moderate 3 Moderate 3 Moderate 3 Moderate G3 Moderate 4 Severe 4 Serious 4 Serious 4 Serious 4 Severe G4 Severe 5 Very severe 5 Very serious 5 Very serious 5 Very serious 5 Very severe G5 Very severe 6 Partial collapse 6 Partial collapse 6 Partial collapse 6 Partial collapse 7 Total collapse 7 Total collapse 7 Total collapse 7 Total collapse classification to the Moderate class instead of a worse class, as categorized the structure as Severe due to the typology, entity, would be expected. Cooper’s(2008) approach, in contrast to and extent of the damage. the previous two classifications, only considers the width of In summary, although the six methods focus on different the cracks that affect the external façades of structures. features caused by the movement that influences the structure, However, although this approach does not consider the settle- the damage was classified as Moderate, except for the Del ment that affects the internal or hidden portions of the struc- Soldato et al. (2017) approach that considers it as Severe, tures, it categorizes this building as Class 3 (comparable to a reflecting some consistency in terms of the damage Moderate) on the opening and the frequency of the cracks. assessment. The DPC method (Baggio et al. 2009), which also considers The second building is located on the left flank of the land- the extension of damage that affects the structures, allows a slide and is formerly connected to another adjacent structure more precise assessment of the damage. The structure shows but is now separated by a gaping construction joint (blue ar- cracks assessed as very important (D4-D5) for one portion rows Fig. 12b). The building is currently abandoned, the dam- and, for the remaining 2/3, occasional cracks (D1). To evalu- age to the structure includes relevant (e.g., see the red arrows ate the edifices sensu strictu, the conversion matrix combines in Fig. 12b) and open cracks and distortions of walls and the different contributions from the severity and the extent of elements as well as losses of material. The application of the the damage in order to produce a result comparable to that of six approaches shows three different levels of damage the previous approach. The new approach (Del Soldato et al. classification for this structure. The differences can be 2017) that combines all previous methods allows the analysis explained considering the parameters considered by the to be performed in more detail, including the extension of the various authors. According to Alexander (1986)and damage and the frequency and the opening of the cracks. The Chiocchio et al. (1997), the grade of damage is evaluated as evaluation of the damage allows for an assessment of the Moderate. Chiocchio et al. (1997) consider centimeters as the entire level of damage for the entire building. This approach unit to describe the opening of the cracks and include severe Fig. 12 Damage assessment for two buildings located in the study area by means of different approaches: a) three-level con- crete structure located close to the landslide crown; b) two-level masonry building positioned on the left flank of the landslide. Both edifices were classified ac- cording to the (1) Burland et al. (1977), (2) Alexander (1986), (3) Chiocchio et al. (1997), (4) Cooper (2008), (5) Baggio et al. (2009), and (6) Del Soldato et al. (2017) approaches. Damage are highlighted by red arrows, and open joints between the nearby structures are shown in blue Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) damage in the intermediate class. Similarly, Alexander’sclas- surveyor cannot enter private property, and he/she can assess sification (1986) considers cracks that affect structural the damage only from the outside, considering obstacles due elements and distortion angles to belong to the Moderate to vegetation or gates. This consideration is important during class. The approaches described by Burland (1977)and the application of damage classifications to correctly assess Cooper et al. (2008) categorize the recorded damage to struc- their severity, although several of the schemes consider the tures in terms of the width and number of cracks more severe- internal conditions of walls and the degree of pavement incli- ly than the two previously mentioned schemes, and the inves- nation. These data are particularity difficult to analyze during tigated building falls into the Severe rank. The classifications preliminary field campaigns or surveys that examine a great proposed by the DPC (Baggio et al. 2009) and Del Soldato et number of buildings, except for emergency interventions in al. (2017) are the only two that classified the building as Very restricted areas. Several factors, such as permission to access severe. The severity and conservative results from these two private properties, fenced areas, and damage hidden by vege- approaches could be justified by their original aim to provide tation, have to be considered during the interpretation of build- quick assessments of fitness for human habitation. In addition, ing damage maps. The restriction of access to the structure to they are unique in that they consider the extension of the better investigate the damage situation could be considered a damage with respect to the entire structure combined with strong limitation of the approach since access to private prop- severity. The entity of the damage is confirmed by the conser- erties is usually only permitted in case of emergency. vation status of the structure, which was abandoned for several Information regarding the crack pattern that affects the internal years. portion of the structures can improve the damage classifica- For some structures, it should be possible to make a com- tions and, if available, they must be implemented for a better parison between previous and future surveys (e.g., see Fig. 10) evaluation of the damage. in order to detect the evolution of the damage and the struc- The evaluation of the damage extent used in the DPC ap- tural conditions through time. Monitoring of the widening of proach (Baggio et al. 2009), despite its apparent lack of sim- cracks and damage to the facilities is also useful for ensuring plicity in overcoming the abovementioned difficulties, was the safety of residents as well as for understanding the tempo- demonstrated to be a powerful improvement to better evaluate ral evolution of the landslide and reducing the possible occur- structures that were differently affected by the damage. rence of additional damage. Furthermore, the contribution of Cooper’s methodology The Cooper (2008) and Del Soldato et al. (2017)ap- (2008), which also allows assessment of the landslide ground proaches also take facilities, such as walls and sidewalk, in damage, is an important element for providing better descrip- addition to the edifices, into consideration in the classification tions of the landslide-induced damage that affects an area. approach. In this work, structures and infrastructure were con- All of the benefits and constraints of the five critical ana- sidered using all methods, and it is very interesting to note that lyzed classifications highlighted above should be used to cre- elements different from the edifices were categorized as the ate a new categorization. A novel approach (Del Soldato et al. highest damage levels (Very severe or Partial collapse). The 2017) was recently published according to the results of the results of investigating further elements with respect to the applications of the literature methods in different sites; it edifices, such as sidewalks, ground fractures and walls, are maintained a division into two parts of the structure in order important for better delineating the extension of territory in- to consider the extent of the damage, the width of the cracks in volved in instabilities, mainly in rural areas as those investi- millimeters and the a posteriori classification of affected build- gated in this work. ings. The application of the new approach is more focused on All of the applied methods revealed some benefits and the identification and categorization of the severity of the constraints. For example, the use of millimeters as a unit for damage that affects the structures, in addition to its extent, measuring the widening of cracks (Baggio et al. 2009; considering the difficulties of access to private dwellings dur- Burland 1977;Cooper 2008) was found to be better than the ing the survey. use of centimeters (Alexander 1986; Chiocchio et al. 1997). The graduation of the damage severity beyond preliminary The evaluation of cracks affecting the foundations (Alexander damage assessments based on external features, can be used 1986), where possible, was found to be useful, even if very for different purposes to improve the understanding of study rarely applicable. Almost all of the methods, except those sites if combined with other information (Infante et al. 2016). described by Cooper (2008) and Del Soldato et al. (2017), Starting with the building and facility categorization, some do not consider the importance of the external visibility of preventive measures can be improved to avoid the occurrence the damage in their descriptions. Notably, all of the conducted of further damage in inventoried landslide-prone areas. In field campaigns allowed surveying the damage recognizable areas where possible landslide-induced damages have been from the outsides of the structures; almost all the surveyed recognized, the development of inventory maps and suscepti- structures are abandoned or access was denied by the owners. bility maps should be considered to improve the knowledge of This is a highly relevant issue because, in most cases, the the region and to support future planning decisions (Lee et al. M. Del Soldato et al. 2003; Di Martire et al. 2012; Guillard and Zezere 2012; approaches were devised to categorize the level of damage Righini et al. 2012; Bianchini et al. 2016). Furthermore, it that affects buildings, and despite a similar description of the could be a fundamental support for state legal procedures to damage, the involvement of various parameters allows differ- assess and reduce the risk of landslides and to increase the ences in the building classifications. resilience of infrastructure through more efficient design. The differences observed in the resulting maps were Some examples include updating urban development plans discussed based on the characteristics of the approaches as and the obligation to perform geotechnical investigations, in- well as the locations and the features of the buildings in- cluding stability analysis, in areas close to buildings damaged volved. The most complete and appropriate method for the by landslides. In the end, to prevent increasing economic area of interest was put into practice, even if a better solution losses, some reinforcing measures based on the effects suf- might have been to merge different features of existing ap- fered by the structures close to undamaged buildings, e.g., proaches to homogenize the procedure and to avoid some by means of underpinning, should be considered if the struc- drawbacks. The difference in classification of structures and tures are located in areas susceptible to landslides. Notably, infrastructure, as well as in ground fractures for the two more the area of study is principally rural, and the number of struc- recent approaches, depended on the different parameters used tures and infrastructure is low. The same comparison of dif- in the classifications once the data were collected. Several ferent methods conducted in an urbanized area could be more considerations that involved the identification of the cracks, consistent, but it has to be considered that the majority of the possibility of surveying the damage in private dwellings, landslides affect low-urban areas. For this reason, the resulting and the main information that has to be recorded to achieve classification appears to be partially mottled in some cases, good and reliable building classifications, were also discussed whereas for built up areas, the higher number of analyzed in order to extract the limitations and the strengths of each structures exhibit a more homogenous classification. This is method. confirmed by comparing the upper portion of the landslide, To summarize, the best method for describing the where several contractions are present, to the other two damage level and the real situation of the structures exanimated sectors with sparse structures. However, the as- seems to be the recent method developed according to sessment of damage is independent of the number of the con- the drawbacks and the benefits of each applied approach. structions investigated inasmuch any applied method was The strength of this approach resulted in the ability to comparative, but all of the approaches were based on the rec- investigate the severity of the cracks, considering several ognition and analysis of the fractures affecting an edifice. features of previous methods, combined with the exten- Corrective measures to restore damaged buildings or to sion of the damage and the categorization of the ground intervene in the activity and the continued evolution of the fractures that can help define the area involved in the phenomenon. This classification offers a simpler assess- mass movement are difficult to suggest on the basis of structural damage classifications alone. To pursue these ment of cracks to be carried out during field surveys goals, specific structural analyses must be performed, and based on observable and clear signs as well as taking the improvement described by Cooper (2008) and slightly into account reference widths and an a posteriori classi- modified by Del Soldato et al. (2017), which involves catego- fication of the structures by considering the effects of the rizing ground surface fractures, in addition to hydrogeological ruptures. and geomorphological studies, can help to select which mea- Ultimately, some considerations of the importance and the sures to adopt and to design better measures after landslides usefulness of the building damage data were performed. The are reactivated. information that can be extracted from the resulting maps can assist in managing and planning prevention and remedial ac- tions implemented in different phases and to avoid possible Conclusions casualties. Some examples include implementing structural and non-structural preventive measures in susceptible areas, Six existing classification methods for landslide-induced dam- monitoring landslide affected areas, providing support to local age were presented, compared, and applied to the structures administrators for planning and promulgating legislative re- and infrastructure within and close to the Colle Lapponi-Piano strictions, and helping private and local authorities renovate Ovetta landslide, in the municipality of Agnone (Molise re- damaged structures or evaluate the possibility of moving some gion, southern Italy). A total number of 30 buildings, two structures and facilities. walls, three concrete emplacements, and one electrical mast were investigated in order to classify the severity of damage Acknowledgements The authors thank the University of Florence for and to investigate the main benefits and drawbacks of each funding Dr. Matteo Del Soldato during a PhD research period in the Department of Civil Engineering at the University of Alicante. The au- method by a comparison of the resulting classifications to thors also thank the Spanish Ministry of Economy, Industry and evaluate their effectiveness in damage assessment. All of the Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy) Competitiveness (MINECO), the State Agency of Research (AEI) and the Cruden DM, Varnes DJ (1996) Landslides: investigation and mitigation. European Funds for Regional Development (FEDER) under projects Chapt 3. Landslide types and processes transportation research TEC2017-85244-C2-1-P and TIN2014-55413-C2-2-P and the Spanish board special report, p 247 Ministry of Education, Culture and Sport under project PRX17/00439. Del Soldato M, Bianchini S, Calcaterra D, De Vita P, Di Martire D, Tomás R, Casagli N (2017) A new approach for landslide-induced damage Open Access This article is distributed under the terms of the Creative assessment. Geomatics Nat Hazards Risk:1–14 Commons Attribution 4.0 International License (http:// Di Martire D, De Rosa M, Pesce V, Santangelo MA, Calcaterra D (2012) creativecommons.org/licenses/by/4.0/), which permits unrestricted use, Landslide hazard and land management in high-density urban areas distribution, and reproduction in any medium, provided you give appro- of Campania region, Italy. Nat Hazards Earth Syst Sci 12(4):905– priate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 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