基于修正Mohr-Coulomb屈服准则的冻结砂土损伤本构模型

A damage constitutive model for frozen sandy soils based on modified Mohr-Coulomb yield criterion

为了探讨冻土的强度和变形特性以及反映低围压下的应变软化和高围压下的应变硬化现象,建立不同围压影响下的冻结砂土损伤本构模型,其能合理解释冻土内部微裂隙向宏观破碎带转化过程。通过引入修正Mohr-Coulomb屈服准则来描述冻土微元强度破坏准则,利用冻土内部微缺陷分布的离散性和随机性特点,假设微元强度服从Weibull随机分布,并根据统计学和连续损伤力学理论建立能反映冻土破损全过程的损伤本构模型。通过低温三轴试验数据确定模型参数值,讨论Weibull分布参数n和F_0的物理意义,并修正分布参数随围压的变化规律;讨论并分析冻结砂土的黏聚力c、内摩擦角φ和损伤变量D随围压变化的演化规律。最后将模型预测结果与试验值进行对比,表明该模型能够较好地模拟冻结砂土应力–应变全过程曲线,并能反映随围压的增大曲线由应变软化逐渐向应变硬化过渡的现象;同时模拟了体积变形曲线,并能反映随围压的增大体变曲线由剪胀向剪缩转变特性。

In order to investigate the strengths and deformation properties of frozen sandy soils,a damage constitutive model under different confining pressures was established to describe the strain softening under lower confining pressures, the strain hardening under higher confining pressures,and the transition process from the internal micro-fissures to macro-shear bands. The strength criterion for the micro-element of frozen sandy soil is described by the modified Mohr-Coulomb yield criterion. Due to the discreteness and randomness of the internal micro-defects and micro-fissures,an assumption is made that the distribution of the micro-element strength for frozen sandy soil obeys Weibull function. Meanwhile,a stochastic damage constitutive model is established to reflect the whole breakage process under the ambient loads,based upon the theoretical knowledge of the statistical theory and the continuum damage mechanics（CDM）. The parameters are determined from the cryogenic triaxial compression tests. The distribution parameters of n and F_0,along with their variation with confining pressures,are discussed in detail. In addition,the cohesion c,the internal friction angle j and the damage variable D are analyzed under the different confining pressures. Finally,comparisons between the predicted results and experimental data demonstrate that the modified model can simulate well the whole stress-strain curves,reflect the transition process from strain softening to strain hardening, predict reasonably the volumetric strain-axial strain curves,especially both the dilatant behaviors under relatively low confining pressures and the compressive characteristics under high confining pressures.