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Background: In April 2016, Kumamoto City, Japan, and its surroundings were hit by a sequence of strong and th devastating earthquakes including two significant events, one on April 14 , 2016, at 21:26 JST (Mw6.2) and the th other on April 16 , 2016, at 01:25 JST (Mw7.0). These disasters caused 120 fatalities (including indirect fatalities), 2337 people injured and 177,914 residential houses were damaged. This paper aims to ascertain the damage to residential housesand buildingscausedbyliquefactionduringthisearthquake and suggests possible mitigation methods. th th Results: Field reconnaissance was conducted in the target area on May 27 –30 , 2016. The post-earthquake inclination angle and the tilt direction of 68 affected houses and buildings in the liquefied sites in Kumamoto City were measured by using a laser rangefinder (Leica DISTO D 510). Ground structure and condition were also determined from topographic maps, bore data and the calculated liquefaction resistance factor, F . Conclusions: Based on this investigation, the inclination angle of the houses in the target area seems to be related to the type of building structure and their foundation as well to the local ground composition. The tilt direction has a tendency to be associated with the location of the nearby river. The results presented could be useful to develop future liquefaction mitigation measures for detached residential houses. Keywords: The 2016 Kumamoto earthquake, Liquefaction, Field investigation, Residential houses and building damage, Inclination angle Background and some of these were quite large with an intensity th At 21:26 JST on April 14 , 2016, a strong earthquake of greater than Mw5. Figure 1a shows the location of the Mw6.2 with focal depth 11 km below the ground surface earthquake epicenter (Anon 2016a) and Fig. 1b and c struck along the Hinagu fault in Kumamoto Prefecture, show the estimated seismic intensity distribution for the on the island of Kyushu, Japan. The strongest ground two major earthquakes, foreshock and mainshock, motion recorded was about 1590 gal in Mashiki Town. respectively (Anon 2016b) and (Anon 2016c). This earthquake proved to be merely a foreshock. Due to these earthquakes, much damage was triggered th Twenty-eight hours later, on April 16 , 2016, at 01:25 by ground liquefaction that occurred in Kumamoto City JST, on the Futagawa Fault zone in the same area, a and surrounding area of the Kumamoto Prefecture, such stronger earthquake of Mw7.0 occurred with focal depth as rupturing and cracking of the ground surface and of 12 km. The maximum ground motion recorded was ground subsidence which resulted in the settlement of about 1791 gal in the town of Ozu. It was also reported buildings and residential houses. In many major previous that there had been a number of aftershocks continued earthquakes, the resulting liquefaction often caused damage through differential settlement which eventually led to permanent tilting of buildings and structural * Correspondence: firstname.lastname@example.org damage as seen in the 2011 Great East Japan earthquake Kanazawa University, Kakuma-Machi, Kanazawa-Shi, Ishikawa Prefecture 920 1192, Japan disaster. Massive liquefaction-induced damage appeared Tadulako University, Bumi Tadulako Tondo Campus, Palu, Central Sulawesi in the city of Urayasu, where more than 9000 residential 94118, Indonesia houses were affected. This major catastrophe leads to an Full list of author information is available at the end of the article © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 2 of 12 Fig. 1 a Epicenters distribution map; b Foreshock estimated seismic intensity distribution map; c Mainshock estimated seismic intensity distribution map awareness and the importance of safe housing design, investigation, information and data were obtained by particularly against liquefaction. As a result, research measuring the structural inclination angles and their related to liquefaction countermeasures became more direction. In addition, interviews of affected parties in intensified. Currently, many companies and research the southern and eastern region of Kumamoto City, institutes are working on developing liquefaction counter- where a lot of liquefaction-induced damage reportedly measure for buildings and for residential houses. Several occurred were also undertaken. researches and studies have been conducted related to the The inclination direction and angle of 68 houses and impact of liquefaction on residential houses during earth- buildings were measured. Using the field survey data, quakes, such as the 2010–2011 Christchurch earthquakes combined with ground sounding data of the surveyed (Cubrinovski et al. 2012), the 2011 Tohoku Pacific sites, the liquefaction risk was estimated and will be earthquake (Tokimatsu & Katsumata 2012) and the much used to clarify the relationship between liquefaction earlier study of the 1990 Luzon earthquake (Tokimatsu et damage andgroundcondition.Furthermore,itismay al. 1994). Various liquefaction countermeasure methods also be useful to develop new liquefaction counter- had been proposed, for example, implementing shallow measures for residential houses. Figure 2 displays the ground improvement (Tani et al. 2015), using a sandy soil liquefaction points and liquefaction-induced damage con- layer (Koseki et al. 2015), installing sheet-pile walls around firmed in Kumamoto City by the field survey (Shigeki et the housing foundations (Rasouli et al. 2015) and by using al. 2016). One of the examples of liquefaction occur- log pile under foundations (Yoshida et al. 2012). rence can be seen in Fig. 3, in which the house experi- Liquefaction-induced damage also occurred and was a enced ground subsidence due to liquefaction and serious problem in certain areas in Kumamoto City during became tilted. the 2016 Kumamoto earthquake. Building on previous experience, field reconnaissance was conducted in the Methods th th target area from May 27 to 30 , 2016 to investigate the Outline of the survey effects of liquefaction on differential settlement and tilting In order to observe the impact of liquefaction on resi- of buildings and residential housing. In this field dential houses and buildings in the 2016 Kumamoto Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 3 of 12 Fig. 2 Liquefaction occurrence reported Earthquake, measurement of the tilt angle and tilt dir- ection of 68 houses and buildings were performed in Kumamoto City such as Akitsu, Chikami, and Karikusa where the damage to the tilted houses was marked. The surveyed sites can be seen in Fig. 4. as well as in the topography classification map of Kumamoto City which was published at the J-SHIS earthquake hazard station shown in Fig. 5 (Anon 2016d). As can be seen on this map, the Akitsu area consists of marshland, while Chikami and Karikusaareas are composedof natural embankments as well as marshland. Both of these regions are mostly formed from sand and have shallow groundwater tables. Due to these geological factors, these areas are liquefaction prone during earthquakes. In this field survey, the tilt angle and tilt direction of the outer walls of the buildings were measured using a Fig. 3 Example of ground subsidence due to liquefaction laser rangefinder (Leica DISTO D 510). Figure 6 shows Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 4 of 12 Fig. 4 Survey location Fig. 5 Topography classification map of Kumamoto City Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 5 of 12 site bore data and that of the surrounding area. In addition, using bore data, soil classification and SPT N- value, the liquefaction resistance factor, F at the designed horizontal seismic intensity of K = 0.3 was calculated to hgL determine the liquefaction potential of the ground. Figure 7a shows the location of the bore log while Fig. 7b presents borehole data obtained at Akitsu. As can be seen in this figure, the groundwater level is 2 m below the ground surface. The embankment layer lies at a depth of 6.2 m and at a depth of more than 6.2 m, the ground is composed of sand and silt layers. Bore data at this site were available only to a depth of 10 m, but this Fig. 6 Measurement points of the building data was sufficient to show that the ground consists of an embankment and sand layers which has the potential the measurement loci of the houses. To obtain more to liquefy. The calculated SPT N-value showed that the comprehensivedataabout the situation at thetimeof ground was in a very loose condition. The calculation re- the earthquake and liquefaction occurrences such as sult of the safety factor against liquefaction, F , in Akitsu sand boiling, interviews of the residents was also can be seen in Fig. 7c. Based on the resultant F value, undertaken. the Akitsu area has a low risk of liquefaction to a depth Based on the survey results, the relationship between of 5 m, as F values are higher than 1. In contrast, it has ground geology, building structure and foundation type a high potential for liquefaction at a depth of more than and the tilt of the structures will be clarified. It is hoped 6 m since it is composed of sand and sandy silt layers that these findings can be used in the future to develop with an F value lower than 1. liquefaction countermeasure methods, particularly for Eight houses were measured in this area. Figure 8 residential houses. shows the measurement results of their tilt angle and tilt direction. In this figure, the tilt angle is indicated by a Results color difference for every 0.5° and the direction of inclin- Akitsu area ation is marked by an arrow. The tilt angle used is the The first location surveyed was Mashima the residential largest angle of all points measured in each house. Inter- complex in Akitsu, which is located along the riverbank estingly, a few houses assessed in this area were inclined on the south side of the Kiyama River. The ground in the same direction, which was the location of the structure of these areas was also examined by using the river. This implies that the damage was caused not only ab c Fig. 7 a Bore log site in Akitsu; b Borehole data obtained in Akitsu; c FL values calculation result for Akitsu area Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 6 of 12 Fig. 8 The tilt angle and direction measurement result in Akitsu by the subsided soils under the structure but also by the ground subsidence occurred, building B only experienced liquefaction occurrence at the riverside area located in minor inclination and minor vertical gap development due front of the houses. to the insignificant differential settlement of its foundation. Figure 9 shows the state of the house after the earthquake This is because this building was supported by a foundation struck and shows that the house became tilted toward the of piles. Figure 12 shows the pile foundations that support river. Furthermore, as can be seen in Fig. 10, the lateral building B. Based on this result, it is thought that the foun- movement also occurred toward the river side at this site. dation type also influenced the degree of inclination of As a result, adjacent houses tend to be tilted in the same building structures. direction with a lateral spreading direction. Figure 11 pre- sents the summary of the structure types and the damage Chikami and Karikusa area in this area. As for building A, it was inclined 3.6° to the Chikami and Karikusa are located in the southern part north and 3.7° to the east as there was substantial ground of Kumamoto City. Figure 13a and b show the bore log subsidence on the north side and different settlement of site and bore data acquired in Chikami and Karikusa the foundation occurred. Ground subsidence at the north area, respectively. The depth of the groundwater level is side also occurred in buildings C and D and similarly to as shallow as 2.15 m. The soil layers are composed of building A, these buildings tilted to the north. Although landfill from 0 to 1.5 m, sand and silt from 1.5 m to Fig. 9 The tilt condition of the house in Akitsu after the earthquake struck Fig. 10 The occurrence of lateral spreading at the river side, Akitsu Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 7 of 12 ab cd Fig. 11 The summary of the structure type and damage level (Buildings A, B, C and D in Fig. 8) in Akitsu 20 m depth below the ground surface. It can be seen pillar the side of the road naming it as the Chikami bridge. that SPT N-value near to the ground surface is also very It substantiates the assumption that this area was previ- low, so it can be said that this ground has a high risk of ously a river and provides a major reason why this area liquefaction, especially from the ground surface down to suffered severe damage due to liquefaction. a depth of around 12.5 m. Figure 17 shows the measurement results of the inclin- Figure 13c gives the F values for Chikami and Karikusa ation angle and tilt direction of the buildings in Chikami areas. Based on calculated F value its potential to liquefy area. There is a tendency for houses experiencing large is moderately high to a depth of about 12.5 m below the tilt angles were located on the adjacent site. It can also ground surface as it is composed mostly of sand and has be seen from this figure that the direction of inclination F values of less than 1, specifically near the surface. Gen- is to the southeast where the river used to be. Structure erally, the potentially liquefiable ground surface may lead types and building damage are summarized in Fig. 18. to structural damage related to differential settlement and Differential settlement occurred in both steel framed structure tilting because sand boiling has a high potential and wooden framed buildings. The four buildings, A, B, to take place. C, and D are taller than other building in their vicinity, In order to ascertain ground conditions in this area, as a result, the tilt angle and the damage inflicted were geological profiles of other two bore logs are observed in substantial. Buildings B and C were tilted so as to appear the adjacent site. The result obtained were much the to be attracted to each other like magnets. This was same, as shown in Figs. 14 and 15. probably caused by the combined weight of the two It was determined that the liquefaction damage in this adjacent buildings resulting in a greater settlement on area was distributed along a longitudinal strip because the neighboring side. It also seems that the non-uniform there was a former river on the north–south side of this settlements were influenced by the weight of the struc- site. This liquefiable zone was spread over 5 km in ture and the position of its center of mass. For building length and 50 to 100 m in width, allowing ground sub- D, the north side wall was severely damaged resulting in sidence and sand boiling. Figure 16 shows a guide a large inclination. Figure 19 gives the tilt angles and tilt directions of the houses in the Karikusa area. Similarly, in this area, many buildings experienced an inclination toward the east. Figure 20 shows the summary of the structural forms and building damage in this area. The building with the largest inclination angle is building B, which was a one storey building. There was no significant wall or struc- tural damage to this building, but a lot of boiled sand traces remained around the building, indicating a large amount of sand boiling had occurred. Buildings A, C, and D were inclined to the east. Discussion In Akitsu area, using the sounding data and the calcu- lated F value, the ground at a depth of more than 5 m Fig. 12 The pile foundation of the house which experienced minor below the ground surface, was categorized as poten- inclination in Akitsu tially liquefiable. Liquefaction that occurred in this Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 8 of 12 ab c Fig. 13 a Bore log site in Chikami and Karikusa; b Borehole data obtained; c FL values calculation result for Chikami and Karikusa area area was mainly affected by the very loose silt and sand In Chikami and Karikusa area, one of the liquefaction layer at a depth of around 6 m below the ground sur- occurrences was sand boil. Boiled sand traces remained face, and the existence of the Kiyama river as well. It at the side of the road and around the houses surveyed. can be seen on the ground, the lateral movement This sand boiling took place because the ground at this appeared on the riverside area and also soft ground area is mostly composed of the sand, and from the with high potential of liquefaction was present near ground surface to a depth of 12 m was categorized as the ground surface. As a result, ground subsidence and potentially liquefiable. Furthermore, liquefaction was differential settlement of houses did indeed occur in also affected by the former river on the north–south side this location. of this area. This potentially liquefiable sand on the ab c Fig. 14 a Bore log site in Chikami and Karikusa; b Borehole data obtained; c FL values calculation result for Chikami and Karikusa area Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 9 of 12 ab c Fig. 15 a Bore log site in Chikami and Karikusa; b Borehole data obtained; c FL values calculation result for Chikami and Karikusa area ground surface may lead to structural damage related to the structure but the geological condition of the ground structure tilting due to sand boiling. as well. Based on this, the liquefaction risk determined using In the interview with the residents, many considered bore data and the value of F was roughly in agreement moving due to a high risk of re-liquefaction of the with the damage that occurred. Therefore, in order to ground. It was thought there was little likelihood of mitigate liquefaction in the future, it will be necessary to applying countermeasures to their houses because of detect the location of weak underground layers. The the associated difficulties in doing so and the high cost degree of the damage sustained by houses even within of the countermeasures. In addition, residents felt un- nearby locations depended on the type of building struc- comfortable with a house tilt angle of 1° or more and ture and its foundation type. Consequently, in order to even worse, the house became hard to live in if the select appropriate liquefaction mitigation measures for inclination angle exceeding 2°. existing structures such as detached residential houses, Previously, in the 2011 Great East Japan Earthquake, it is necessary to consider the characteristics not only of enormous liquefaction damage occurred in Urayasu City, Fig. 16 The guide pillar of the former Chikami bridge Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 10 of 12 Fig. 17 The tilt angle and direction measurement result in Chikami Chiba Prefecture, in which was about 85% of the city though some of the buildings were situated in neighboring was damaged. Because of the huge area that suffered areas, the damage that occurred due to liquefaction to liquefaction, a large-scale liquefaction countermeasure each building also varied, depending on the factors was undertaken, in the form of underground walls. On mentioned earlier, for example, the type of the structure the other hand, Kumamoto City, unlike Urayasu City, and its foundation type. the occurrence of liquefaction was not centralized in one Based on the different conditions of liquefaction that large area but scattered in small separate regions. Even occurred in these two cities, the recommended mitigation ab c d Fig. 18 The summary of the structure type and damage level (Buildings A, B, C and D in Fig. 17) in Chikami Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 11 of 12 Fig. 19 The tilt angle and direction measurement result in Karikusa ab c d Fig. 20 The summary of the structure type and damage level (Buildings A, B, C and D in Fig. 19) in Karikusa Setiawan et al. Geoenvironmental Disasters (2017) 4:13 Page 12 of 12 methods applicable to Kumamoto City and surrounding Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in areas will be different to the methods that employed in published maps and institutional affiliations. Urayasu City. It is thought that will be useful to devise and develop liquefaction countermeasures for existing Author details Kanazawa University, Kakuma-Machi, Kanazawa-Shi, Ishikawa Prefecture 920 detached residential houses and buildings, in addition to 1192, Japan. Tadulako University, Bumi Tadulako Tondo Campus, Palu, the large-scale mitigation technique applied in Kumamoto 3 Central Sulawesi 94118, Indonesia. National Institute of Technology, Fukui City and nearby areas. College, Geshi-chou, Sabae, Fukui Prefecture 916 8507, Japan. Nowadays, we are doing a research related to liquefac- Received: 10 December 2016 Accepted: 30 March 2017 tion countermeasure methods that can be utilized for detached residential houses. References Anon. 2016a. Distribution of epicenters plotted on geological maps in Kumamoto Prefecture. Available at: http://g-ever.org/updates/?p=285. Conclusion Accessed 29 Nov 2016. In the field reconnaissance, 68 houses were measured Anon. 2016b. Estimated seismic intensity distribution map (April 14th, 2016). and the tilt angle and tilt direction were described on Available at: http://www.data.jma.go.jp/svd/eew/data/suikei/201604142126_ 741/201604142126_741_1.html. Accessed 29 Nov 2016. the map presented. Although this survey was in a narrow Anon. 2016c. Estimated seismic intensity distribution map (April 16, 2016). area, it was found that there was a great variance in the Available at: http://www.data.jma.go.jp/svd/eew/data/suikei/201604160125_ degree of inclination of the buildings within that area. 741/201604160125_741_1.html. Accessed 25 Nov 2016. Anon. 2016d. Kumamoto topography classification map. Available at: http://www. The extent of the damage was found to relate to such j-shis.bosai.go.jp/. Accessed 29 Nov 2016. factors as differences in the type of building structure Cubrinovski, M., D. Henderson, and B. Bradley. 2012. Liquefaction Impacts in and their foundations, the weight of the structure as well Residential Areas in the 2010–2011 Christchurch Earthquakes, One year after 2011 Great East Japan Earthquake: International Symposium on Engineering as the ground condition. As a result, the degree of the Lessons Learned from the Giant Earthquake, 1–14. damage differed from building to building within the Koseki, J., K. Wakamatsu, S. Sawada, and K. Matsushita. 2015. Liquefaction-induced same location, for example, while buildings supported by damage to houses and its countermeasures at Minami-Kurihashi in Kuki City during the 2011 Tohoku Earthquake, Japan. Soil Dynamics and Earthquake conventional foundations experienced large inclination, Engineering 79: 391–400. the pile-supported building only suffered minor inclin- Rasouli, R., I. Towhata, and T. Hayashida. 2015. Mitigation of seismic settlement ation. In addition, it was found that topography affects of light surface structures by installation of sheet-pile walls around the foundation. Soil Dynamics and Earthquake Engineering 72: 108–118. the direction of inclination which in this case was mostly Shigeki, S., K. Wakamatsu, K. Ozawa, and H. Fujiwara. 2016. Liquefied sites during toward the river location. Furthermore, some of the the 2016 Kumamoto Earthquake. Available at: https://confit.atlas.jp/guide/ houses and buildings which experienced large tilt angles event-img/jpgu2016/MIS34-26P87/public/pdf. Accessed 29 Nov 2016. Tani, K., T. Kiyota, K. Matsushita, T. Hashimoto, A. Yamamoto, H. Takeuchi, T. Noda, were located on the adjacent site. In order to devise and H. Kiku, and J. Obayashi. 2015. Liquefaction countermeasures by shallow develop a new and effective liquefaction countermeasures ground improvement for houses and their cost analysis. Soil Dynamics and for residential houses, it is recommended that a compre- Earthquake Engineering 79: 401–414. Tokimatsu, K., and K. Katsumata. 2012. Liquefaction-Induced Damade To Buildings hensive investigation be undertaken taking into consider- in Urayasu City During the 2011 Tohoku Pacific Eathquake, The International ation such factors as implementation methods, costs, Symposium on Engineering Lessons learned from the 2011 Great East Japan material availability as well as structure and foundation earthquake, 665–674. Tokimatsu, B.K., H. Kojima, and S. Kuwayama. 1994. Liquefaction-induced damage type while not forgetting the underlying geological struc- to buildings in 1990 Luzon earthquake. Journal of Geotechnical Engineering ture of the ground as well the surrounding topography. 120(2): 290–307. These considerations may produce liquefaction counter- Yoshida, M., M. Miyajima, and A. Numata. 2012. Proceedings of the Tenth International Symposium on Mitigation of Geo-disasters in Asia in Matsue measure methods suitable for detached residential houses. Conference,55–67. Acknowledgements This research was financially supported by JSPS KAKENHI Grant Number: 25289135. The authors thank Mr. Naoki Nomura of the Nihonkai Consultant Co. Ltd. and Mr. Kazutaka Shichiroumaru of the Kokudo Kaihatu Center Co. Ltd. for supported in this field reconnaissance. The authors also thank Submit your manuscript to a Directorate of Resources for Science, Technology, and Higher Education, journal and beneﬁ t from: Ministry of Research, Technology and Higher Education of Indonesia for the scholarship. 7 Convenient online submission 7 Rigorous peer review Authors’ contributions 7 Immediate publication on acceptance HS, YS, MN, MM, and MY participated in the field reconnaissance and 7 Open access: articles freely available online discussed the results of the survey. HS drafted the manuscript. YS and MN prepared the topographic map of Kumamoto City and boring data 7 High visibility within the ﬁ eld processing. All authors have read and approved the final manuscript. 7 Retaining the copyright to your article Competing interests Submit your next manuscript at 7 springeropen.com The authors declare that they have no competing interests.
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