Vane Shear Behavior of Soft Bangkok Clay

Abstract The field vane shear test is one of the most common in situ tests to obtain the undrained shear strength of soft clay. Uncoupling of the torque generated by the soil resistance along the vertical and horizontal planes of the vane has been done by conducting conventional direct shear test and newly developed vertical direct shear test on the soil. From the shear stress-displacement relationship of the direct shear tests, simple analysis is performed to simulate the field vane behavior at various depths. The results of the simulation agree well with those obtained from the field vane tests on soft Bangkok clay. The conventional method of computing the undrained shear strength of the field vane shear based on the maximum torque is close to the equivalent average value from the shear box tests. A special laboratory triaxial vane apparatus was also used to study the shearing behavior of the soft clay with the capability of Ko-consolidating the sample before conducting the vane shear test. The results of the triaxial vane tests were also compared with the predictions. The predicted torque values are lower than the experimental data for the same angle of rotation.