Functioning and precipitation-displacement modelling of rainfall-induced deep-seated landslides subject to creep deformation

Abstract

International audienceWe propose an approach to study the hydro-mechanical behaviour and evolution of rainfall-induced deep-seated landslides subjected to creep deformation by combining signal processing and modelling. The method is applied to the Séchilienne landslide in the French Alps, where precipitation and displacement have been monitored for 20 years. Wavelet analysis is first applied on precipitation and recharge as inputs and then on displacement time-series decomposed into trend and detrended signals as outputs. Results show that the detrended displacement is better linked to the recharge signal than to the total precipitation signal. The infra-annual detrended displacement is generated by high precipitation events, whereas annual and multi-annual variations are rather linked to recharge variations and thus to groundwater processes. This leads to conceptualise the system into a twolayer aquifer constituted of a perched aquifer (reactive aquifer responsible of high-frequency displacements) and a deep aquifer(inertial aquifer responsible of low-frequency displacements). In a second step, a new lumped model (GLIDE) coupling groundwater and a creep deformation model is applied to simulate displacement on three extensometer stations. The application of the GLIDE model gives good performance, validating most of the preliminary functioning hypotheses. Our results show that groundwater fluctuations can explain the displacement periodic variations as well as the long-term creep exponential trend. In the case of deep-seated landslides, this displacement trend is interpreted as the consequence of the weakening of the rock mechanical properties due to repeated actions of the groundwater pressure

Damage‐Based Time‐Dependent Modeling of Paraglacial to Postglacial Progressive Failure of Large Rock Slopes

“…Large rock slope failures are commonly delayed with respect to deglaciation, supporting the hypothesis that they undergo progressive failure in subcritical stress conditions (Brideau et al, ; Chigira, ; Eberhardt et al, ). These are mirrored by a commonly observed time‐dependent “slope creep” (Emery, ), characterized by rather constant, low displacement rates to which seasonal accelerations are often superimposed (Crosta & Agliardi, ; Vallet et al, ). The latter are usually interpreted as evidence of coupling between hydrological triggers and landslide systems (Crosta et al, ; Preisig et al, 2016; Vallet et al, ).…”

“…These are mirrored by a commonly observed time‐dependent “slope creep” (Emery, ), characterized by rather constant, low displacement rates to which seasonal accelerations are often superimposed (Crosta & Agliardi, ; Vallet et al, ). The latter are usually interpreted as evidence of coupling between hydrological triggers and landslide systems (Crosta et al, ; Preisig et al, 2016; Vallet et al, ). Although movements progressing to catastrophic collapse may result from rock mass failure without external forcing (i.e., tertiary creep; Rose & Hungr, ; Saito & Uezawa, ; Voight, ; Zavodni & Broadbent, ), hydromechanical coupling has been recognized to play an increasingly important role as rockslides attain mature stages of evolution (Crosta et al, ).…”

“…During postglacial evolution, external triggers including rainfall and snowmelt can promote or contribute to a range of instabilities reaching up to entire valley flanks, with severe impacts on human lives, activities and infrastructures (Agliardi et al, ; Crosta & Agliardi, ; Crosta et al, ; Dortch et al, ; Helmstetter & Garambois, ; Zangerl et al, ). Large “differentiated” (i.e., mature) rockslides, characterized by well‐developed basal shear zones and highly fractured and permeable unstable masses, show the most distinctive sensitivity of displacement patterns to hydrological triggers (Corominas et al, ; Crosta et al, ; Vallet et al, ). Nevertheless, the geomechanical and hydrological legacies of glacial and paraglacial processes and their influence on the postglacial evolution of rock slope instabilities are still poorly known.…”

“…In principle, this would require tracking the mechanical and hydrological history of alpine rock slopes to the occurrence of a “mature” rockslide, through a variably long period of transition (Figure ). In practice, rockslide forecasting mostly relies on analytical, statistical, or numerical models accounting for the hydromechanical landslide response to rainfall or snowmelt (Cappa et al, ; Crosta et al, ; Guglielmi et al, ; Preisig et al, 2016; Vallet et al, ; Zangerl et al, ), based on a rockslide model derived from geotechnical and geophysical characterization. Nevertheless, the long‐term evolution of the geometry, internal structure, strength, and hydrology of alpine rocks slopes is usually unknown and poorly described by models focused on the analysis of onset mechanisms of rock slope failure and their topographic, lithological, structural, and climatic controls (Agliardi et al, ; Ambrosi & Crosta, ).…”

The Coupling Effect of Rainfall and Reservoir Water Level Decline on the Baijiabao Landslide in the Three Gorges Reservoir Area, China

“…Sun et al [8] simulated the hydraulic-mechanic coupling process of Sanmendong landslide by software product ABAQUS and confirmed that the combined result of reservoir water level fluctuation and rainfall could primarily account for the increase of displacement of this landslide. Vallet et al [9] studied the hydromechanical behavior and evolution of rainfall-induced landslides subjected to creep deformation. The previous researches are mainly based on the steady-state method, by calculating variables of the model under different 2 Geofluids reservoir water levels, so as to approximately simulate the dynamic process of reservoir water level variation.…”