考虑卸荷速率的K0固结膨胀土应力-应变行为

通过GDS三轴试验系统对K0固结原状南阳膨胀土原状样进行了不同卸荷速率和卸荷路径下的不排水三轴剪切试验，在试验资料的基础上，建立了K0固结膨胀土的初始切线模量Ei和极限偏应力qult与固结应力及卸荷速率的关系式。发现，K0固结膨胀土在卸荷剪切过程中的应力-应变关系曲线呈典型双曲线特征；膨胀土的不排水剪切强度随轴向固结应力及卸荷速率的增加而单调增加；Ei及qult随固结应力及卸荷速率的变化规律与强度基本类似，但Ei随固结应力的增加呈指数增加，而qult则表现为线性增加。通过改进邓肯-张双曲线表达式，建立了K0固结膨胀土下不同卸荷速率时应力-应变关系的预测公式，并进行了模型验证。

Stress-strain behavior of expansive soil under K_0 condition with different unloading rates

A series of undrained triaxial shear tests on undisturbed Nanyang expansive clay under saturated K0 condition have been performed. Two different stress paths, reduced triaxial compression (RTC) and reduced triaxial extension (RTE), four axial consolidation stress (80kPa, 160kPa, 240kPa and 320kPa), and three stress rate (0.02 kPa/min, 0.2kPa/min and 2kPa/min) were configured by GDS triaxial system. Based on the experimental data, the relationship among initial tangent modulus Ei, ultimate deviatoric stress qult of expansive soil, consolidation stress, and unloading rate was established. The results showed that the stress-strain relationship of expansive soil was hyperbolic along the unloading paths in both RTC test and RTE test. The shear strength increased as the stress rate and confined pressure increased monotonously. The changes of initial tangent modulus Ei and the ultimate principal stress difference qult were similar to the shear strength. The initial tangent modulus Ei increased exponentially and the ultimate principal stress difference qult increased linearly as the confined pressure increases. Based on the modified Duncan-Chang model, the prediction formula considering the stress rate was built for expansive soil under K0 consolidation condition.