Study on Shear Strength Tests and Uniformed Constitutive Model of Shear Stress-Shear Displacement for Unsaturated Soils

The unconsolidated-undrained fast shear tests of saturated-unsaturated remolded soil samples under different moisture content (which is 1.1%, 10.1%, 14.9%, 19.9%, 24.2%, 29.9%, 37.7%, respectively) and normal stress (which is 50kPa, 100kPa, 200kPa, 300kPa, 400kPa, respectively) were studied by the modified SDJ-1-type strain direct shear apparatus and U.S. Lab VIEW data acquisition system. The shear strength parameters of unsaturated soil samples, i.e. general cohesion and general internal friction angle were obtained based on Mohr-Coulomb strength theory. The test results showed that the general cohesion firstly increased and then reduced with the moisture content increasing, and the general internal friction angle increased with the moisture content decreasing. The shear stress-shear displacement constitutive equation of the unsaturated soil was established based on equal displacement assumptions and the test results. The fitted results coincided with the experimental results very well. The concept of general shear strength parameters was proposed in the paper, and would provide a simple and practical method to obtain the strength parameters for engineering practice.