This study aims at exploring the influences of shear velocity and drainage conditions on the strength of kaolin clay. A low to high velocity rotary shear apparatus was used to measure the apparent friction coefficient of wet kaolin clay under a normal stress of 1 MPa. The shear velocity ranged from 10-6 to 1 m/s. The drainage conditions include radial, single and double drainage conditions. The results show a lower strength for the radial drainage condition (close to the undrain condition) than the ones measured under single drainage test conditions covering the whole velocity spectrum. Notably, the friction coefficient dropped rapidly in the early stage (<200 s) of radial drainage condition but increased gradually, which can be related to the excess pore pressure dissipation. The results of this study are relevant to the study of large landslides, from creeping tuning to catastrophic failure.
Keywords: Excess pore water pressure, shear speed, friction coefficient, kaolin clay/kaolinite.