Luca Schilirò

Prediction of shallow landslide occurrence: validation of a physically-based approach through a real case study

In recent years, physically-based numerical models have frequently been used in the framework of early-warning systems devoted to rainfall-induced landslide hazard monitoring and mitigation. For this reason, in this work we describe the potential of SLIP (Shallow Landslides Instability Prediction), a simplified physically-based model for the analysis of shallow landslide occurrence. In order to test the reliability of this model, a back analysis of recent landslide events occurred in the study area (located SW of Messina, northeastern Sicily, Italy) on October 1st, 2009 was performed. The simulation results have been compared with those obtained for the same event by using TRIGRS, another well-established model for shallow landslide prediction. Afterwards, a simulation over a 2-year span period has been performed for the same area, with the aim of evaluating the performance of SLIP as early warning tool. The results confirm the good predictive capability of the model, both in terms of spatial and temporal prediction of the instability phenomena. For this reason, we recommend an operating procedure for the real-time definition of shallow landslide triggering scenarios at the catchment scale, which is based on the use of SLIP calibrated through a specific multi-methodological approach.

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

ABSTRACT In 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.

The Contribution of Terrestrial Laser Scanning to the Analysis of Cliff Slope Stability in Sugano (Central Italy)

In this work, we describe a comprehensive approach aimed at assessing the slope stability conditions of a tuff cliff located below the village of Sugano (Central Italy) starting from remote geomechanical analysis on high-resolution 3D point clouds collected by terrestrial laser scanner (TLS) surveys. Firstly, the identification of the main joint systems has been made through both manual and automatic analyses on the 3D slope model resulting from the surveys. Afterwards, the identified joint sets were considered to evaluate the slope stability conditions by attributing safety factor (SF) values to the typical rock blocks whose kinematic was proved as compatible with tests for toppling under two independent triggering conditions: hydrostatic water pressure within the joints and seismic action. The results from the remote investigation of the cliff slope provide geometrical information of the blocks more susceptible to instability and pointed out that limit equilibrium condition can be achieved for potential triggering scenarios in the whole outcropping slope.

Role of Land Use in Landslide Initiation on Terraced Slopes: Inferences from Numerical Modelling

Land use/land cover is widely considered as a relevant factor for shallow landslide occurrence; therefore, in this work we used a physically-based model, whose input parameters have been evaluated taking into account the land use setting. In detail, assuming that vegetation affects the surface runoff and infiltration rate, as well as increases the shear strength of soil due to the root reinforcement effect, we calibrated several specific model parameters (such as friction angle, cohesion and hydraulic conductivity) by varying their values within a reasonable range, on the basis of a detailed land use map specifically prepared for some small coastal basins located in the Cinque Terre area (eastern Liguria, Italy). Since this area is characterized by the widespread presence of agricultural terraces, mainly abandoned, their degree of abandonment has also been considered. Different numerical simulations have been performed with TRIGRS (transient rainfall infiltration and grid-based slope stability), a well-known regional, physically-based stability model, with the aim of reproducing the landslide event occurred in the study area on October 25th, 2011. The safety factor (FS) maps obtained by using TRIGRS have been compared with the inventory map of the landslides triggered during the event. Then, a ROC (receiver operating characteristic) curve analysis has been carried out in order to quantify the performance of the model. The obtained results emphasize the influence of land use in shallow landslide occurrence.

A deterministic approach for shallow landslide triggering scenarios in the southern Messina area (north-eastern Sicily, Italy)

The aim of this work is to define different triggering scenarios for shallow landslides through a physically-based approach. In particular, numerical simulations have been performed using TRIGRS model for the back-analysis of a reference landslide event, i.e. the disaster occurred in the Giampilieri area (located approximately SW of Messina in north-eastern Sicily, Italy) on October 1st, 2009. The simulation results, expressed in terms of safety factor (FS), describe a temporal evolution of the slope instability substantially consistent with the real event. With regard to the spatial distribution of the slope failures, the model is able to identify quite well the 2009 landslide phenomena, since 48.5% of the source areas and 79.8% of the stable areas are correctly classified. After the calibration of the physically-based model, different triggering scenarios have been reconstructed by varying the rainfall input, on the basis of the hourly rainfall probability curves obtained through a statistical analysis of historical rainfall data. The results indicate that even rainfalls with low return period and short duration (i.e. one hour) can produce a considerable instability level, in agree with the high number of landslide/flood events recorded in the study area since the last century.