The Role of Initial Soil Conditions in Shallow Landslide Triggering: Insights from Physically Based Approaches

L Schilirò,C Esposito,G Scarascia Mugnozza,G Poueme Djueyep

doi:10.1155/2019/2453786

Abstract

In the last years, the shallow landslide phenomenon has increasingly been investigated through physically based models, which try to extend over large-area simplified slope stability analyses using physical and mechanical parameters of the involved material. However, the parameterization of such models is usually challenging even at the slope scale, due to the numerous parameters involved in the failure mechanism. In particular, considering the scale of the phenomenon, the role of transient hydrology is essential. For this reason, in this work we present the outcome of different experimental tests conducted on a soil slope model with a sloping flume. The tested material was sampled on Monte Mario Hill (Rome, Central Italy), an area which has been frequently affected by rainfall-induced landslide events in the past. In this respect, we also performed a physically based numerical analysis at the field conditions, in order to evaluate the response of the terrain to a recent extreme rainfall event. The results of the flume tests show that, for the same material, two different triggering mechanisms (i.e., uprise of a temporary water table and advance of the wetting front) occur by varying the initial water content only. At the same time, the results of the numerical simulations indicate that clayey sand and lean clay are the soil types mostly influenced by the abovementioned rainfall event, since the initial moisture conditions enhance the formation of a wide wetting front within the soil profile.

Highlights

Many of the rainfall-induced landslides occurring all over the world are shallow-type; namely, the sliding surface is located at a depth from a few decimeters to some meters
The outcome of the experiments has been analyzed in relation to the results provided by HYDRUS-1D [35], a USDA (United States Department of Agriculture) Salinity Laboratory software package which can simulate the water flow into unsaturated porous media resulting from a rainfall event
With regard to the failure mode, the data deriving from the soil moisture and pore water pressure sensors indicate two potential triggering mechanisms to variations of the initial water content, i.e., failure induced by uprise of a temporary perched water table and by the advance of the wetting front in the case of relatively low and relatively high initial soil moisture, respectively

Summary

Introduction

Many of the rainfall-induced landslides occurring all over the world are shallow-type; namely, the sliding surface is located at a depth from a few decimeters to some meters. They generally occur in response to prolonged intense rainfall events and involve either residual weathered soils or transported colluvial deposits This type of landslides represents a widespread hazard that frequently results in considerable damage to infrastructure and human losses in many mountainous regions of the world, especially in areas characterized by the widespread presence of natural (e.g., [1,2,3]) and/or humanreworked soil cover (e.g., [4,5,6]). The infiltrating water flow may cause both the development of a temporary perched water table, usually at the contact between the soil cover and the less permeable bedrock [14], and a decrease of the resisting effect (apparent cohesion) induced by increasing positive water pressure values in the unsaturated portion [15, 16] In this respect, it has been well recognized that matric suction can play a crucial role in the stability of unsaturated soil slopes [17]. Considering the complexity of this research topic, a considerable amount of experiments has been conducted on understanding the behavior of waterinduced shallow landslides under controlled laboratory

Methods

Results

Conclusion