Disintegration law of strongly weathered purple mudstone on the surface of the drawdown area under conditions of Three Gorges Reservoir operation

Abstract

Mudstones locating on surfaces of drawdown area of a bank slope in Three Gorges Reservoir (TGR) are prone to disintegrate under cyclic wetting-drying (WD) conditions during the reservoir operation, which will have adverse effects on the slope stability. In order to study disintegration law of the mudstones, 9 strongly weathered purple mudstone (SWPM) samples from the Middle Triassic Badong group (T2b) in TGR area were collected to conduct laboratory-based cyclic WD experiments under ambient stresses (0.0 MPa, 0.5 MPa and 1.0 MPa) using a novel self-developed experimental system. Meanwhile, grain size distribution curves of materials slaking form the mudstone samples were measured after each WD cycle. Grain size distribution curves and disintegration phenomena of the SWPM samples show that disintegration degree decreases with the increase of ambient stresses when the mudstone undergoes the same wetting-drying cycles, and it increases with the increase of wetting-drying cycles under the same ambient stress. A new index, disintegration coefficient (Dt), is proposed to describe the disintegration degrees of the mudstone under conditions of reservoir operation (WD cycles and ambient stresses). The changes of disintegration coefficient suggest that the SWPM on the surface of the drawdown area is more likely to disintegrate under smaller ambient stress in the course of reservoir operation.