An Analysis of Rainfall-Induced Landslide in Colluvial and Eluvial Soils Overlying Xigeda Strata, Southwestern Sichuan, China

In late-July, 2005, a series of thunderstorms dropped 10 cm of rain in a 72-h period over southwestern Sichuan province. The storms also triggered more than 17 shallow landslides along the Lama Stream, about 2.5km from Jiuxiang Town, in Hanyuan County. Almost all of the landslides were translational, occurring along the contact between colluvial and eluvial soils and the underlying bedrock (claystones, mudstones, siltstones). 1# landslide was selected in the affected area for a detailed study of the shallow landslides. The record was made of the stratigraphy, slope geometry, landslide dimensions, hydrologic conditions, and contributing factors. Both colluvial soils and underlying bedrock were sampled for laboratory investigations, which included determination of natural water content, specific gravity, natural density, Atterberg limits, coefficient of consolidation, permeability, and shear-strength parameters. Data from laboratory tests were used to perform stability analyses by the infinite-slope analysis method, with respect to varying slope angles, strength parameters, and thicknesses of saturated colluvial and eluvial soils. The results of the study indicate that the shallow landslides of Xigeda strata occurred when the colluvial soils reached 90% to 100% saturation, depending upon the slope angles. It provides a basis for taking reasonable reinforcement measures for the landslides.