Abstract: 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.

Key words: K0 consolidation, expansive clay, stress rate, stress-strain behavior