上海第4层黏土力学特性的弹塑性本构模拟

Elastoplastic constitutive modelling for mechanical behavior of Shanghai 4th layer clay

上海第4层黏土是典型的结构性海相软土,用一个本构模型统一地模拟不同应力路径下的力学特性对数值计算具有重要意义。对UNIFIED模型的结构性及超固结发展函数进行了改进,并提出了一种确定原状土材料参数和初始状态的方法。为了验证修正模型的正确性,用块状取土法取得上海第4层原状土样,进行了固结试验和三轴排水、不排水剪切试验。通过比较试验结果和本构模拟结果,明确了新的本构模型仅用一组材料参数就能统一地模拟上海第4层黏土在固结、排水及不排水三轴试验得到的应力-应变关系。模拟结果揭示了上海第4层黏土的结构比较稳定,即使在经历三轴剪切发生35%轴应变后仍能保持较高位的结构性。

Shanghai 4th layer clay is a typical marine clay with distinct structure. It is helpful for numerical analysis to develop a constitutive model which uses one set of parameters to simulate the mechanical behavior of the clay subject to various stress paths. In this study, the evolution rules of structure and overconsolidation of UNIFIED constitutive model are modified. A new method is proposed to obtain the values of initial state and material parameters of undisturbed soils. In order to verify the modified model, the blocking sampling method is used to obtain undisturbed samples of Shanghai 4th layer clay. The conventional oedometer tests and drained/undrained triaxial compression tests are conducted on the 4th layer clay. A comparison between the test results and constitutive modelling results shows that the modified model and proposed method can simulate the stress-strain behaviors in the oedometer and triaxial tests of 4th layer clay properly, using only one set of parameters. It also shown that the structure of Shanghai 4th layer clay remains stable and the structure remains unchanged even after triaxial shearing at an axial strain of 35%.