Environmental Earth Sciences (2017) 76:808
Rainfall‑induced landslides by decit eld matric suction
in unsaturated soil slopes
· Yongmin Kim
· Sangseom Jeong
· Moonhyun Hong
Received: 22 February 2017 / Accepted: 13 November 2017 / Published online: 30 November 2017
© Springer-Verlag GmbH Germany, part of Springer Nature 2017
Landslides are mainly triggered by decrease in the matric suction with deepening the wetting band by rainfall inﬁltrations.
This paper reports rainfall-induced landslides in partially saturated soil slopes through a ﬁeld study. A comprehensive analysis
on Umyeonsan (Mt.) landslides in 2011 was highlighted. The incident involves the collapse of unsaturated soil slopes under
extreme-rainfall event. Fundamental studies on the mechanism and the cause of landslides were carried out. A number of
technical ﬁndings are of interest, including the failure mechanism of a depth of soil and eﬀect of groundwater ﬂow, the down-
ward movement of wetting band and the increase of groundwater level. Based on this, an integrated analysis methodology
for a rainfall-induced landslide is proposed in this paper that incorporates the ﬁeld matric suction for obtaining hydraulic
parameters of unsaturated soil. The ﬁeld matric suction is shown to govern the rate of change in the water inﬁltration for the
landslide analysis with respect to an antecedent rainfall. Special attention was given to a one-dimensional inﬁltration model to
determine the wetting band depth in the absence of the ﬁeld matric suction. The results indicate that landslide activities were
primarily dependent on rainfall inﬁltration, soil properties, slope geometries, vegetation, and groundwater table positions.
The proposed methodology has clearly demonstrated both shallow and deep-seated landslides and shows good agreement
with the results of landslide investigations.
Keywords Slope · Landslide · Rainfall · Inﬁltration · Unsaturated soil
Rainfall-induced landslides are generally deﬁned as trave-
ling processes of soils in mountainous areas, particularly
in areas covered by shallow soils of diﬀerent grading and
origin. (Jeong et al. 2008; Cascini et al. 2010; Kim and
Jeong 2017). These areas are often recorded in pyroclastic
deposits in Central America and New Zealand (Capra et al.
2003; Ekanayake and Phillps 2002), weathered soils in Hong
Kong and Japan (Take et al. 2004; Wang et al. 2002), weath-
ered colluvial deposits in Hong Kong and Korea (Fuchu
et al. 1999; Park et al. 2013). In particular, ﬂow-type land-
slides (Hungr et al. 2001) represent signiﬁcant threats to
lives, livelihoods and infrastructure in mountainous areas.
For example, when South Korea experienced heavy rain-
fall recorded in June and July 2011, some 151 landslides
occurred in the Umyeonsan Mt. region aﬀecting 13 villages.
Because the mountain is located in urban area of Seoul,
these landslides had signiﬁcant impact on society.
The triggering mechanisms of natural slope failures gen-
erally governed by a complex interaction between hydrologi-
cal and geotechnical processes, which depends on irregular
topography, hydro-geotechnical contexts by properties and
boundary conditions, such as permeability and the initial
state of the slope (Sorbino and Nicotera 2013). The rain-
fall is one of the most frequent landslides triggering factors,
which can directly inﬁltrate the slope surface or indirectly
provide increases in groundwater from the bedrock or aqui-
tard (Kim et al. 2014). In a geotechnical perspective, the
main reason of slope failures is the loss of eﬀective stress
with the loss of matric suction caused by rainfall inﬁltration
in soil. Many researchers (Fredlund et al. 2012; Jeong et al.
2008; Kim et al. 2014) studied rainfall-induced landslides
based on laboratory and ﬁeld tests as well as numerical
* Sangseom Jeong
Department of Civil and Environmental Engineering, Yonsei
University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722,
Republic of Korea
School of Civil and Environmental Engineering, Nanyang
Technological University, Singapore 639798, Singapore