Shear strength features of unsaturated clayey sand by lab test

To study the shear feature of the clayey sand subgrade, the equations of soil–water characteristic curve with different net mean stresses were established based on laboratory test and non-linear elastic theory. The laboratory result shows that the net mean stress has significantly affected on the soil–water characteristic curve shape. The greater the net mean stress, the smaller moisture content of soil. The shear features of clayey sand were also figured out using triaxial equipment with mini air and water pressure sensors in non-drained and non-exhaust state. The results of research indicate that the net confining pressure and moisture content have significant effect on the strength, deformation, and yield feature of unsaturated clayey sand. The shear strength increases with the growth of net confining pressure in case of constant moisture content. The cohesion and friction angle of soil become larger with the increase of moisture content less than optimum content; while the water content is greater than the optimum water content, they show the opposite trend. The unsaturated clayey sand shows obvious dilatancy deformation in shearing. In the phase of shear contraction, the shear stress increases with the growth of suction and net confining pressure, which declines after it reach the peak point. Results of this research will be a benefit for the engineer.