An Attempt to Predict the Effective Angle of Internal Friction for Remolded Clayey Soils Using the Vane Shear Test: Some Important Implications

Identifying strength parameters under drained conditions is crucial for monitoring and evaluating long-term soil deformations caused by structures built on or in soils. Geotechnical engineers carry out direct shear tests (DSTs) and triaxial tests (TAs) in the laboratory to identify strength parameters under such conditions. However, it can take considerable time to ascertain the failure envelope of even a single soil in the TA tests commonly used to evaluate drained conditions. This study explores whether the effective internal friction angle (phi ')-as one of the drained shear strength parameters of remolded soils-can be identified with a vane shear test (VST) at very low (down to 0.001/min) rotation speeds, which is easy to implement and takes a relatively shorter time. For this aim, 18 different remolded soil samples with a wide range of plasticity were prepared using static compaction in the laboratory. DST tests were conducted under drained conditions to evaluate the drained shear strengths of the remolded soil samples. VST results indicate that the peak shear strength decreases with the rotation speed as expected. Shear strengths obtained from the slowest VSTs were correlated with phi ' s from DSTs. While the results were not encouraging, it was observed that the results of VSTs still could be used in a predictive equation for phi ' which, as a function of LL and total density as well as VST strength parameter, the regression coefficient rose to 0.92. Some effective cohesion intercepts were observed during DSTs, which in turn somewhat reduce the predicted phi ' s.

Automated summary

Identifying strength parameters under drained conditions is crucial for monitoring and evaluating long-term soil deformations caused by structures built on or in soils. This study explores the possibility of using a vane shear test at low rotation speeds to identify the effective internal friction angle of remolded soils. The results indicate that the vane shear test can be used to predict phi', but the predictions may be influenced by certain factors.