Effects of Soil Porosity on Slope Stability and Debris Flow Runout at a Weathered Granitic Hillslope

Abstract

Accurate models of rainfall infiltration are needed for analysis and prediction of slope failure induced by heavy rainfall. In this study, a numerical model was developed to simulate two-dimensional rainwater infiltration into an unsaturated hillslope, the formation of a saturated zone, and the resultant changes in slope stability. This model was subsequently used to analyze the effects of soil porosity parameters (i.e., saturated soil water content u s and effective soil porosity [ESP]) on the occurrence of slope failure, the moisture conditions of the displaced material, and the movement of debris flow on weathered granitic hillslopes. We conducted the simulations by imposing various conditions of rainfall, initial wetness of the slope, soil thickness, and slope gradient. Results showed that when the surface soil of a slope has a relatively large ESP value, it has a greater capacity for holding water and therefore delays deeper water infiltration into the subsurface. Consequently, the increase in pore water pressure in the subsurface at a greater depth is also delayed. In this manner, the greater ESP value contributes to delaying slope failure. Under small storm conditions, slope failure tends not to occur when the surface soil has a relatively large ESP value. However, a greater ESP tends to increase the water content of the displaced matter, which results in faster and longer travel distances, and more deposition of debris flow, thus increasing the risk of damage in downstream regions.

Effect of rainfall infiltration into unsaturated soil using soil column

“…The event of rainfall infiltration mechanism is complex due to its high nonlinearity of soil water characteristic and soil permeability [8]. This is support by [5,10] which mentioned that the complexity of rainfall infiltration mechanism is due to the primary moisture state of the soil, water retaining capacity of the soil, soil porosity, evaporation rate and others. Therefore, in order to understand the behavior of soil under various rainfall intensity and duration, the needs to study the infiltration mechanisms are vital.…”

“…This caused changes of soil structure as the cohesive strength between soils particles decreased due to lower matric suction. This event will affect soil instability of a slope [2][3][5][6]. In [6][7] stated that lower soil slope factor of safety is due to the increasing of rate of infiltration.…”

Quantifying and modeling post-failure sediment yields from laboratory-scale soil erosion and shallow landslide experiments with silty loess

“…Soils in a loose state (i.e. high porosity) have greater water holding capacity and therefore higher pore-pressures are usually generated upon compression and shearing (Iverson and LaHusen, 1989;Iverson, 1997;Iverson et al, 2000;Mukhlisin et al, 2006). Increases in pore-pressure are also related to the development of rapid shearing (Okura et al, 2002;Sassa, 2001, 2003).…”

3 Dimension Real Time Images of Rainfall Infiltration Into Unsaturated Soil Slope

“…The study of main parameters such as initial moisture content, soil water retention ability, soil porosity and others is vital for the understanding of soil behavior when subjected to various rainfall intensity and duration [3], [5],.…”