Abstract:

In order to study the effect of strain rate on the mechanical properties of undisturbed expansive soil, the consolidated undrained triaxial shear tests at different rates and confining pressures were conducted by the GDS triaxial test system. The variations of stress-strain curves, pore water pressure, shear strength and failure pattern influenced by strain rates were analyzed. The results show that the stress-strain curves of expansive soil show a strain harden pattern at different strain rates. With the increase of strain rate, the undrained shear strength increases monotonically. After introducing the strain rate parameter ρ _0.9, it is found that the undrained strength increases by 14.3% to 23.2% for a 10-fold change in strain rate, with an average value of 18.4%. The strain rate has less effect on the pore water pressure at a low confining pressure, and the development trend of pore water pressure changes from softening to hardening type with increase confining pressure, and the peak pore water pressure decreases with increase strain rate. The strain rate effect of undisturbed expansive soil is closely related to its fissures. The failure pattern is manifested by the coexistence of main and sub shear zones at smaller strain rates, while the failure pattern is only the main shear zone at larger strain rates. The presence of fissures or multiple shear zones enhance the strain rate effect of expansive soil dramatically.

Key words: undisturbed expansive soil, strain rate, undrained shear strength, pore water pressure