Spatially distributed landslide triggering analyses accounting for coupled infiltration and volume change
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Zhichen Song I Xiang Li I José J. Lizárraga I Lianheng Zhao I Giuseppe Buscarnera
Spatially distributed landslide triggering analyses accounting for coupled infiltration and volume change
Abstract Rainfall infiltration in unsaturated slopes alters the effective stress through pore water pressure changes, thus causing ground deformation. Although important to assess the timescale over which the margin of safety of a slope decreases, such coupled processes are rarely accounted in the context of spatially distributed hazard assessment procedures. In this paper, a physically based, spatially distributed model accounting for full hydro-mechanical coupling is discussed. The model relies on a vectorized finite element (FE) solver to calculate the stability of deformable unsaturated infinite slopes subjected to transient flow. First, the FE solver is used to study the response of individual slopes to a prolonged rainfall for three scenarios (i.e., rigid, swelling, and collapsible soil). Then, the model is used in the context of spatially distributed computations to assess spatiotemporal variations of factor of safety over a large area. For this purpose, a series of shallow landslides occurred in a mountainous landscape covered by collapsible loess deposits in northwestern China was used as test site. The analyses show that hydromechanical couplings affect the performance of the model in terms of computed failure time and areal extent of the unstable zones. Specifically, volume collapse due to suction decrease is found to reduce the time of failure compared with uncoupled computations obtained for a rigid soil scenario. The most substantial advantages of using coupled analyses have been reported with reference to gentle slopes, for which the higher rate of suction reduction driven by volume change was crucial to capture landslide source areas that would otherwise be overlooked by uncoupled analyses. The proposed methodology offers a complete tool for landslide hazard assessment, in that it incorporates sources of coupling between hydrology and mechanics that are crucial to replicate the physics of landslide initiation. Keywords Hydro-mechanical coupling distributed analysis . Unsaturated soils
. Infiltration . Spatially . Collapse
Introduction Rainfall-induced landslides are among the most widespread and frequent hazards around the world (Petley 2012). Water infiltration is indeed a well-known source of soil strength deterioration, either by increasing pore water pressure (hence reducing the frictional resistance) or by changing the soil rheology through enhanced deformability and wetting-induced volume change (Alonso et al. 1990; Rahardjo and Fredlund 1995; Mihalache and Buscarnera 2016). Specifically, as water infiltrates in an unsaturated soil, suction and degree of saturation vary, eventually giving rise to alterations of the stresses acting on the skeleton and volume changes. At the same time, changes in the state of saturation controlled by the volume change response may affect the hydraulic characteristics of the
