原状膨胀土剪切力学特性的应变速率效应

为研究应变速率对原状膨胀土力学性状的影响，通过GDS三轴试验系统进行了不同速率和围压下的固结不排水三轴剪切试验，分析了应力?应变曲线、孔隙水压力、剪切强度以及破坏模式随应变速率的变化规律。结果表明：不同应变速率下，膨胀土应力?应变曲线均呈应变硬化型。随着应变速率的增加，不排水剪切强度单调递增，引入应变速率参数ρ_0.9后发现，不排水强度增长率为14.3%～23.2%，平均值为18.4%。低围压下，应变速率对孔隙水压力影响较小，随着围压的增大，孔隙水压力的发展趋势由软化型转变为硬化型，孔隙水压力峰值随应变速率的增大而减小。原状膨胀土应变速率效应与其多裂隙性密切相关，破坏形式表现为小应变速率下主剪切带与次剪切带共存，大应变速率下仅有主剪切带，裂隙或多剪切带的出现强化了膨胀土强度的应变速率效应。

Strain rate effect of the shear mechanical properties of undisturbed expansive soil

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.