2002 Volume 111 Issue 3 Pages 416-425
We studied the relations between the lithological properties of bedrock, soil layers, and dimensions of soil slips (depth and slope angle) in slopes on Jurassic granite and Precambrian gneiss in the suburbs of Seoul, Republic of Korea. The slope angle before slippage and the average depth at which slippage initiates are estimated to be about 35-40° and 70-90 cm in granite. The values for gneiss scars are 27-33° and 140-190 cm. Regolith (weathering products) is coarse on slopes underlain by granite and fine on slopes underlain by gneiss, reflecting the grain size of the minerals in the underlying bedrock. Soil layers at the slip (shearing) plane on the granite slope are coarser grained with a larger angle of internal friction (φ) and a smaller cohesion (c) compared to soil layers on the gneiss slope. A slope stability analysis indicates that these properties of soil, themselves derived from weathering, control the difference in dimensions of soil slips found between granite and gneiss.