Shallow landslide initiation on terraced slopes: inferences from a physically based approach

Luca Schilirò,Andrea Cevasco,Carlo Esposito,Gabriele Scarascia Mugnozza

doi:10.1080/19475705.2018.1430066

Abstract

ABSTRACTIn the last years, great efforts have been made to improve the assessment of the temporal and spatial occurrence of rainfall-induced shallow landslides. Therefore, in this paper we used a physically based stability model (TRIGRS) in order to reproduce the landslide event occurred in the Monterosso catchment (Cinque Terre, Eastern Liguria, Italy) on 25 October 2011. The input parameters of the numerical model have been evaluated taking into account the land-use setting and paying specific attention to the evaluation of the spatial variation of soil thickness on terraced areas. The resulting safety factor maps have been compared with the inventory map of the landslides triggered during the event. The simulation results, which have been obtained also considering four different spatial resolutions of the digital terrain model, emphasize the influence of land use in shallow landslide occurrence and indicate the importance of a realistic spatial variation of soil thickness to enhance the reliability of the model. Finally, different triggering scenarios have been defined using hourly rainfall values statistically derived from historical data. The results indicate the proneness of the area to shallow landsliding, given that rainfall events with a relatively low return period (e.g. 25 years) can trigger numerous slope failures.

Highlights

Shallow landslides triggered by rainfall are 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 soil cover and subject to heavy precipitation (Aleotti and Chowdhury 1999; Dai et al 2002; Lin et al 2006)
It can be noted that with the exception of the 1-m ones, the simulations which consider the spatial variation of the soil thickness based on the topographic position index (TPI) method are slightly better than those using the soil thickness resulting from the Saulnier's method (‘SAU’)
The best area under the curve (AUC) result corresponds to the TPIç4-m simulation: for this reason, we analysed the temporal evolution of the instability with these conditions (Table 6)

Summary

Introduction

Shallow landslides triggered by rainfall are 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 soil cover and subject to heavy precipitation (Aleotti and Chowdhury 1999; Dai et al 2002; Lin et al 2006). In order to predict the occurrence of such events, in the last years many attempts have been made to establish a relationship between rainfall and landslides, in particular by means of physically based numerical models. Montgomery and Dietrich 1994; Iverson 2000; Borga et al 2002; Liao et al 2011; Formetta et al 2014; Ho and Lee 2016; Thiery et al 2017), the fundamental controls leading to slope failure driven by rainfall are still not well quantified (Borja et al 2012), and the improvement of current models is still an important research topic (Chang et al 2008). The difficulty of building up reliable mathematical models lies in the numerous variables involved in the triggering process, such as spatial and temporal rainfall variability, mechanical and hydraulic soil properties, slope morphology, vegetation coverage, initial soil suction and moisture (Greco et al 2010).

Methods

Results

Conclusion