基于塑性损伤的黏土岩本构模型及其数值实现

Constitutive model of claystone based on plastic damage and its numerical implementation

黏土岩是深部地下工程中常见的岩土介质,在施工过程中为确保巷道安全开挖,急需开展与其力学特性相关的研究。已有试验研究结果表明黏土岩在三轴压缩试验过程中表现出明显的塑性硬化、软化以及流动特性,同时发现试样在加载过程中内部会产生明显的缺陷,这些缺陷的存在会在一定程度上削弱其力学性能。为建立能描述黏土岩力学现象的模型,以微裂纹作为损伤基元,构建了合理的塑性损伤变量并将其与塑性硬化变量一同引入至修正Drucker-Prager帽盖模型中,建立了新的本构模型。通过ABAQUS平台及其UMAT子程序对该模型进行数值实现,子程序在向后欧拉本构积分算法的基础上引入塑性硬化和损伤变量参与迭代计算,使得屈服面在迭代过程中与应力一同更新(屈服面的大小会随着塑性损伤与硬化变量的更新而变化),直至应力回到屈服面上。采用该模型对常温条件下的黏土岩三轴压缩试验进行数值模拟,并将新模型的计算结果与试验结果进行对比,对比结果显示模拟结果与试验结果大致吻合,说明本文所建立的本构模型可以较好的反映黏土岩的力学特性。最后建立黏土岩隧硐开挖平面模型,采用新模型对开挖过程进行模拟,并对整个模拟过程中损伤变量、应力以及孔隙水压力的演化规律进行分析,模拟结果验证了新模型在地下硐室开挖数值模拟上的适用性。

Claystone is a common geotechnical medium in deep underground engineering project.In order to ensure the safety of tunnel during its excavation,the work which is related to its mechanical properties is required to be studied.The existing test results show that the claystone exhibits some obvious strain-hardening,strain-softening and plastic flow characteristics during the triaxial compression test.At the same time,it is found that the samples produce some obvious defects during the loading process,and the existence of these defects would weaken the mechanical properties.In order to establish a model which can describe the mechanical phenomena of claystone,the micro-crack is used as the damage element to construct a reasonable plastic damage variable.The damage variable is introduced into the modified Drucker-Prager cap model together with the plastic hardening variable to construct a new constitutive model.The model is numerically implemented by the ABAQUS platform and its UMAT subroutine.In the subroutine,the plastic hardening and damage variables are introduced into the iterative calculation based on the backward Euler constitutive integral algorithm,so that the yield surface is updated with the stress in the iterative process until the stress returns to the yield surface(The size of the yield surface changes with the plastic damage and hardening variable).This model is used to simulate the triaxial compression test of claystone under normal temperature,and the simulation results are compared with the experimental results.The comparison results show that the simulation results are in good agreement with the experimental results,indicating that the constitutive model established in this paper can better reflect the mechanical properties of claystone.Finally,the plane excavation model of claystone tunnel is established.The new model is used to simulate the excavation process.The evolution of damage variables,stress and pore water pressure during the whole simulation process is analyzed.The simulation results verify the applicability of the new model in numerical simulation of underground tunnel excavation.