Modelling of landslides in a scree slope induced by groundwater and rainfall

Daisy Lucas,Andreas Kieper,Markus Iten,Heinz Buschor,Sarah M Springman,Ralf Herzog,Amin Askarinejad

doi:10.1680/jphmg.18.00106

Daisy Lucas, Andreas Kieper + Show 5 more

Open Access

https://doi.org/10.1680/jphmg.18.00106

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Abstract

Predicting the trigger of a slope failure of a steep Alpine scree slope in south-west Switzerland is challenging. The groundwater (GW) flow from snow-melting and rainfall infiltration during summer changes the susceptibility to surficial failure, which also depends on the slope angle, bedrock geometry, stratigraphy and the shear strength of the soil. Surficial failure mechanisms are investigated using prototype ground models that integrate input from field monitoring, geological observations and soil properties and account for relevant factors and constraints for physical and numerical modelling. Shallow scree deposits overlying various bedrock configurations (parallel to the slope, with and without a step) were tested under two hydrological regimes: GW flow, and GW combined with additional intense rainfall. Numerical modelling was used to study the parameter combinations that would lead to failure, and worst-case scenarios were defined in terms of the bedrock geometry and hydraulic perturbations. These results were verified using advanced physical modelling techniques in a geotechnical drum centrifuge. Physical modelling results indicated that, for a given GW condition, slope stability decreases (a) as the depth of the soil cover over the bedrock decreases and (b) the higher the bedrock step. Furthermore, a bedrock step impacts the volume and the location of the triggered failure. Rainfall exacerbates the situation.

Highlights

A project was developed by ETH Zürich in collaboration with the Agarn community, Canton Wallis, Switzerland to quantify the hazard associated with the surficial failure of an extensive north-facing Alpine scree slope in the Meretschibach catchment (Lucas et al, 2017; Springman et al, 2015)
An advanced, state-of-the-art physical modelling technique was used to study the impacts of rain and GW flow, coupled with the shape of the bedrock, on the response of the slope
The observations from the physical modelling were supported using the simplified uncoupled hydro (Seep/W) and mechanical (LEM: Slope/W) numerical modelling. & Numerical simulation was useful in studying a wide variety of cases and helped select the worst-case scenarios to be investigated further, and quantified, using centrifuge modelling

Summary

Introduction

A project was developed by ETH Zürich in collaboration with the Agarn community, Canton Wallis, Switzerland to quantify the hazard associated with the surficial failure of an extensive north-facing Alpine scree slope in the Meretschibach catchment (Lucas et al, 2017; Springman et al, 2015). The 33–43° inclined scree slope (Figure 1(a)) is located at the top of the. The stratigraphy of the slope was characterised (Lucas et al, 2017) and a ground model was defined (Figure 1(b)) for use in the physical and numerical simulations. Modelling of landslides in a scree slope induced by groundwater and rainfall Lucas, Herzog, Iten et al. Dry eroded channel Scree slope (IT1–IT4)

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