Influence of Water Content on Shear Strength and Tangential Adhesion Strength of Sand by a Modified Vane Shear Test Device

The shear strength of sand is important to the design and modeling of shield tunneling, and the tangential adhesion strength is a key parameter when determining the pressure gradient along the screw conveyor, the clogging of soil, and the abrasion of the cutting tools. This paper brings up an accurate vane and plate shear test device, which could increase the accuracy of measurements by quantifying and eliminating the influence of torque fluctuation. The peak and residual values of the shear strength and tangential adhesion strength are measured at atmospheric pressure, with water contents from 0% to 25%, and rotation speeds from 0 to 5 r/min. The test results demonstrate that the peak values increase to a maximum value and then decrease with water content. The water content that corresponds to the maximum peak value was between 5% and 20%; the finer the sand, the higher the water content. The ratio between the tangential adhesion strength and shear strength (ratio α) decreases with water content, from approximately 0.7 at a water content of 0% to approximatley 0.4 at 25%. The vane shear test reaches a peak value within 0.17 rotations, and the plate shear test reaches a peak value between 0.25 and 0.55 rotations. Both tests reach residual values after five full rotations. In addition, finer sands have higher shear strengths and higher ratio α.