Analysis of Slope Stability and Debris Flow Run-out

Abstract

Rainfall that triggers debris flow may be defined according to both empirical and physical thresholds. Empirical thresholds are based on historical analysis of the relationship between rainfall and debris flow events, and are a fundamental element of existing real-time warning systems. The most commonly used combinations of rainfall parameters are antecedent rainfall, and the duration, intensity, and cumulative amount of rainfall. To study rainwater infiltration into soil, an understanding of the hydraulic properties of soil is required. Among the soil hydraulic properties, hydraulic conductivity K, a measure of water movement in soil, has been frequently analyzed for its effects on slope stability. The soil water retention model is affected by saturated soil water content qs and residual soil water content qr, in which the difference between qs and qr is the effective soil porosity (ESP). This study presents a numerical model that estimates the rainwater infiltration into unsaturated slopes, the formation of a saturated zone, and the resultant change in slope stability. This model is then used to analyze the effects of soil porosity parameters (i.e., qs, qr, and ESP), on slope failure and the moisture condition of the corrupted material. The effects of antecedent rainfall, initial wetness of the slope, soil thickness, and slope gradient are also analyzed in this study.

Results of simulations with different ESP input data showed that, when the surface soil of a slope has a larger ESP value, the slope has a greater capacity for holding rain water, and delays the infiltration of water into the sub-surface layer. As a result, the increase of pore water pressure in the sub-surface layer is delayed. In this manner, a larger ESP value for the surface layer contributes to a delay in slope failure occurrence. Under a weak storm condition, slope failure tends not to occur if the surface soil has a larger ESP value. However, it was also found that a greater ESP value tends to increase the water content of the corrupted matter, which may result in the occurrence of debris flow, and in long distance transport of the debris. Therefore, under conditions of a greater ESP value, greater damage may be expected once slope failure occurs.

Biography :
Muhammad Mukhlisin is a Professor in the Department of Civil Engineering, Politeknik Negeri Semarang, Indonesia. He received the Bachelor of Engineering degree in civil engineering from Diponegoro University, Semarang, Central Java, Indonesia in 1992 and the Master of Engineering in Hydro Engineering from Gadjah Mada University, Yogyakarta, Indonesia in 1999. He obtained PhD degree from Kyoto University in 2005 under JICA (Japan International Cooperation Agency) scholarship program. From 2008 to 2014, he was a visiting lecturer in Department of Civil and Structural Engineering, Faculty Engineering and Built Environment, Unversiti Kebangsaan Malaysia (UKM) Malaysia and Department of Civil Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi (KMUTT) Thailand on February 2020. Since February 2018 He has been appointed as the Head of International Office of Politeknik Negeri Semarang. He has published more than 180 papers on journals and conferences related to water resources, environmental and natural disaster issues including a number of keynote speakers and special lectures.