描述饱和砂土剪切特性的一个热力学本构模型

A thermodynamic constitutive model for describing shear behavior of saturated sand

砂土的力学特性十分复杂,与其所处的物理状态直接相关,表现为松砂的剪缩以及密砂的剪胀特性,受相对密度和有效围压的共同影响。为有效地描述饱和砂土在不同物理状态下的剪切特性,基于颗粒物质热动力学理论,考虑颗粒层次能量耗散机制,并结合引入状态参数的剪胀方程,发展一个饱和砂土的热力学本构模型。该模型形式较为简单,不涉及屈服准则、流动法则等概念,而是引入颗粒熵和颗粒温度的概念来描述砂土内部的不可逆变形,并通过迁移系数和能量密度函数将饱和砂土内部的能量耗散机制与宏观力学行为建立联系。模型可以反映饱和砂土在剪切过程中由于相对密度和有效围压的变化对土体强度和变形特性的影响。基于模拟计算结果与等向压缩、三轴不排水以及排水剪切试验结果的对比,验证了模型描述饱和砂土剪切特性的能力。

The mechanical properties of sand are very complicated and directly related to its physical state.Generally,it is manifested as shrinkage of loose sand and dilatancy of dense sand,which are affected by both relative density and effective confining pressure.In order to effectively describe the shear behavior of saturated sand under different physical states,based on the theory of thermal dynamics of granular materials and the energy dissipation mechanism at granular level,a thermodynamic constitutive model was proposed combined with the dilatancy equation with state parameters.The model is simple in form,which does not involve the concepts such as yield criterion and flow rule,but it introduces the concepts of granular entropy and granular temperature to describe the irreversible deformation,and establishes a relation between the dissipation mechanism of saturated sand and the macroscopic mechanical behavior through migration coefficients and energy density functions.Thus,the model can describe the influence of relative density and effective confining pressure on the strength and deformation characteristics of saturated sand during shear process.The ability of the model to describe the shear behavior of saturated sand was verified by comparing the results of isotropic compression tests,triaxial undrained,and drained shear tests with simulation results.