Numerical modelling of a creeping landslide using the finite element method: A case study

Kenta Kotani3, A. Wakai2, and D.R. Bhat1
1 JSPS Research Fellow, Graduate School of Science and Engineering, Gunma University, Kiryu, Tenjin-cho 1-5-1, 376-8515, Japan.
2 Professor, Graduate School of Science and Engineering, Gunma University, Kiryu, Tenjin-cho 1-5-1, 376-8515, Japan.
3 Graduate student, Graduate School of Science and Engineering, Gunma University, Kiryu, Tenjin-cho 1-5-1, 376-8515, Japan.

ABSTRACTIn this study, a finite element based numerical method is considered to evaluate the creeping behavior of a creeping
landslide induced by snow melt water. A novel 2D-Elasto-viscoplastic constitutive model is used to simulate thecreeping behavior owing to groundwater level fluctuations of the Tomuro landslide of Gunma, Japan as a case study.
Two new control constitutive parameters are incorporated in the numerical model for the first time to better
understand the creeping behavior of a landslide. Such control constitutive parameters are estimated based on therelation between the total factor of safety, calculated by the various Limit Equilibrium Methods and Finite Element
Method, and the field monitoring displacement rate of the Tomuro landslide. In addition, the snowfall precipitation isalso considered during the calculation of total factor of safety using both limit equilibrium methods and finite
element method. Others required material parameters for landslide simulation are obtained from the field
investigation and laboratory tests of the collected blocked samples. The simulation results of deformation pattern andshear strain pattern are also discussed to understand the creeping behavior of the Tomuro landslide. Moreover, thepredicted and measured time histories of horizontal displacement of the Tomuro landslide are compared for thevalidity of the proposed numerical model, and found in good agreements with each other.
Keywords: finite element simulation; groundwater fluctuation; new control constitutive parameters; creeping
behavior; tomuro creeping landslide

1 INTRODUCTION
Creeping landslides are one of the major
geotechnical hazards. Most of creeping landslide sites
accommodate human settlement and agricultural fields,
roads and highways, bridges and tunnels, nature
conservation sites, and so on (Bhat et al., 2017a and2014a). When the displacement rate of such landslides
is suddenly increased and accelerated, it leads a hugemass failure, which damages human life, property,
nature, and the environment. If a numerical approach topredict the creeping behavior of a landslide is possible,
each damage can be prevented (Bhat et al., 2017a, and2017b). Therefore, study of the creeping behavior of alandslide and associated Geotechnical hazard issues
seems very important.
Creeping landslides are controlled by thegroundwater fluctuations (e.g., Conte et al. 2014;
Picarelli et al. 2004) therefore; groundwaterfluctuations should be incorporated in the numericalsimulation of such landslides (Bhat et al. 2017a and2017b). However, most of previous numerical approach(e.g., Picarelli et al. 2004; Patton 1984) of soil creep
and associated problems are focused on the laboratory
creep tests (i.e., consolidation/oedometer test andtriaxial test), which could not address the fluctuation ofgroundwater level. Based on the theoretical,experimental, and numerical models, a few researches(e.g., Bhat et al. 2016 and 2014b; Picarelli et al. 2004;
Patton 1984) have tried to address these issues; but they
are not fully understood, especially in relation to thedisplacement behavior of a creeping landslide. Huvajand Maghsoudloo (2013) have simulated considering
groundwater fluctuations in different phases tounderstand of displacement behavior of a slow-moving
landslide, but the exact value of the deformation at any
required point (location) couldn’t be captured perfectly.
Recently, a few researchers (e. g., Ishii et al., 2012; Conteet al., 2014; Fernández-Merodo et al., 2014) haveproposedaFEM-based
2D-Elasto-viscoplastic
constitutive model using the field instrumentation andmonitoring results, but they are only considered thesingle control constitutive parameter, estimate based on
the trial and error method, which could not control thedisplacement rate of the landslide, and also far toaddress the realistic field problem of creeping behaviorof the landslide. Therefore, the main objective of thisstudy is to address the above-mentioned problems using
a new FEM-based numerical model, and to study thecreeping behavior of Tomuro landslide induced bysnow melt water as a case study.