Full-scale physical model of landslide triggering

Landslide triggering induced by high-intensity rainfall infiltration in hillslopes is a complex phenomenon that involves hydrological processes operating at different spatio-temporal scales. Empirical methods give rough information about landslide-prone areas, without investigating the theoretical framework needed to achieve an in-depth understanding of the involved physical processes. In this study, we tackle this issue through physical experiments developed in an artificial hillslope realized in the Department of Civil, Environmental and Architectural Engineering of the University of Padua. The structure consists of a reinforced concrete box containing a soil prism with the following maximum dimensions: 3.5 m high, 6 m long, and 2 m wide. In order to analyze and examine the triggered failure state, the experiments are carried out with intensive monitoring of pore water pressure and moisture content response. Subsurface monitoring instruments are installed at several locations and depths to measure downward infiltration and/or a rising groundwater table. We measure the unsaturated soil water pressure as well as positive pore pressures preceding failure in each experiments with six tensiometers. The volumetric water content is determined through six Time Domain Reflectometry probes. Two pressure transducers are located in observation wells to determine the position of the water table in time. Two stream gauges are positioned at the toeslope, for measuring both runoff and subsurface outflow. All data are collected and recorded by an acquisition data system from Campbell Scientific. The artificial hillslope is characterized by well-known and controlled conditions, which are designed to reproduce an ideal set-up susceptible to heavy rainfall landslide. The hydrologic forcing is generated by a rainfall simulator realized with nozzles from Sprying System and. specifically designed to produce a spatially uniform rainfall of intensity ranging from 50 to 150 mm/h. The aim of our experiments is to reproduce the instability trigger that occurs in saturated or partially unsaturated conditions depending on the specific characteristics of the soil and its initial conditions; the retention curve of fine sand and the initial porosity are taken into account to highlight the hydrological condition of the surface layer during the trigger occurrence. Through our experimental setup we can investigate the succession of phases and their magnitude that cause the landslide trigger, in order to understand the instability mechanism that heavy rainfall can induce in fine sandy hillslopes. Particular attention is given on the role of water pressure head, not only with respect to the violation of Coulomb failure within a sloping soil, but also with respect to the subsequent deformation that involves the upper hillslope layers. In particular, we report here on the characterization of the sandy terrain used in the experiments and the preliminary results, together with a first discussion of the observed data.