SHEAR STRENGTH DEGRADATION OF SEMARANG BAWEN CLAY SHALE DUE TO WEATHERING PROCESS

The effect of weathering processes in decreasing the shear strength of clay shale had been done in this study. The drying process of clay shale with sunlight in the laboratory up to 80 days had been conducted to create the conditions of weathered sample. The peak and residual shear strength parameters of unsaturated and saturated clay shale were obtained from triaxial laboratory test, and all samples were tested on each 8 days of weathering process. Decrease of shear strength in peak and residual condition was obtained during 80 days of the drying process. The residual shear strength parameters were distinguished between residual shear strength without stress release and with stress release of confining pressure. The results up to 80 days of unsaturated clay shale showed that the cohesion at peak stress conditions reduced to 30 % based on initial shear strength before the occurrence weathering, while the internal angle friction reduced to 64 %. Residual cohesion without and with stress release reduced to 4 % and 1 %, respectively while residual internal angle friction without and with stress release reduced to 15 % and 5 %. Similar situation also occurs for the saturated clay shale samples.