The effect of weathering process to determination of residual shear strength of clay shale with triaxial multi-stage system

Abstract

The slope failure on clay shale with many joints under a layer of tuff breccia shortly after stress release due to cutting activity have triggered the need to investigate clay shale residual shear strength. A series of triaxial testing on undisturbed samples of clay shale have been performed to determine the residual stress for multi-stage system operation. In the first stage, residual shear strength without stress release were obtained. Then, testing continued by releasing whole-cell pressure. The triaxial test was proceed to the second multi-stage system to obtain residual shear strength parameters. Tests were conducted to investigate the effect of drying process to reduce residual shear strength up to 80 days. During the period, the maximum percentage of residual internal angle friction without stress release (Øurp) and residual internal angle friction with stress release (Øurf) were reduced by 11% and 5%, respectively. Both paremeters are compared to the peak shear strength condition.