Hydraulic properties of co-seismic landslide deposits around the Wenchuan earthquake epicentre: Large-scale column experiments

Abstract

The co-seismic landslides and rock avalanches caused by the 2008 Wenchuan earthquake generated numerous poorly consolidated deposits over a vast area. Rainfall-induced initiation and remobilization of these deposits have resulted in many post-earthquake disasters, such as rapid erosion, flow slides, and debris flows, threatening the local residents. The hydraulic properties of the deposits dominate the evolution of the soil moisture in the slope during rainfall, consequently affecting the initiation and failure types of these geo-disasters. Thus, laboratory tests and infiltration experiments were conducted with material from co-seismic landslide deposits in the Wenjia Gully near the Wenchuan earthquake epicentre. The soil-water characteristic curve (SWCC) of the co-seismic deposit material was determined by a pressure plate extractor and tensiometers. Then, a series of large-scale soil column experiments were conducted with the materials. The results of the experiments showed a relatively high permeability and low matric suction of the co-seismic deposit compared with other soils. The infiltration characteristics of the deposit material with different initial water contents, compactness, and fine particle contents were also analysed and compared. A linear solution of the Green and Ampt equation was employed to estimate the infiltration rate in the deposit during rainfall events, which fit the results of the experiments well. The influence of matric suction on the water absorption and retention capacity was obvious when the moisture content was less than 5%, resulting in a variable evaporation rate and a soil-water hysteresis phenomenon. The results of this study provide reliable experimental evidence with which to evaluate the distribution and evolution of soil moisture in landslide deposits, which is significant for geo-hazard assessments and mitigation works. • Large-scale soil column experiments were conducted to study the hydraulic properties of co-seismic landslide deposits. • The permeability of co-seismic landslide deposits is relatively high, which results in an infiltration rate of 0.174–2.4 m/h. • An algebraic solution of the Green and Ampt equation is used to estimate the evolution of the wetting front. • The evaporation rate is much lower than the infiltration rate due to the increase in matric suction, which results in a soil-water hysteresis.