Abstract
Ring shear tests were performed on high purity clay minerals (montmorillonite, sericite, chlorite and illite) and on mixtures (chlorite-sericite mixtures and montmorillonite-illite mixtures). Montmorillonite exhibited the lowest residual friction angle (3.8°). The residual value was 9.7° for sericite, 11° for chlorite, and 14.5° for illite. The shear strength recovered from the residual state for these pure clay minerals by the second and fifth unloading stages, except for sericite. The recovery ratio of the shear strength was 10% for chlorite and 25% for montmorillonite with σn' of 200kPa. The recovery of the shear strength of montmorillonite correlated closely with swelling. The detected residual strength of these clay minerals did'nt change through five load changes. The residual strength of chlorite-sericite mixture exhibited transitional behavior. The test results when the chlorite content of the mixture was less than 49% exhibited the residual strength of sericite when the chlorite content of the mixture was more than 49%, the mixture exhibited the residual strength of chlorite. Montmorillonite-illite mixture exhibited the residual strength of montmorillonite when the montmorillonite content exceeded 30%. The residual strength of chrolite-sericite mixture is similar to the shear strength of slip surface clay created from weathered greenstone. For montmorillonite-illite mixture, the residual strength was similar to the shear strength of slip surface clay created from weathered Tertialy mudstone.
