冻土非线性断裂破坏过程数值计算分析

冻土具有非线性特征,因此其断裂破坏过程也是非线性的并存在微裂纹损伤区(MDZ),将MDZ简化为虚拟裂纹,并考虑到冻土特性,假定在虚裂纹面上存在着胶结力,提出了冻土断裂破坏的胶结力裂纹模型,并具体讨论了张拉型破坏和压缩破坏的胶结力裂纹模型.其次,依据Paris位移公式,分别推导均布外力作用下,裂纹面上作用有非线性分布胶结力情况的裂纹尖端张开位移一般表达式,进一步导出了三点弯曲梁及压缩破坏的裂尖张开位移表达式,为冻土非线性破坏过程及特征参数的计算提供依据.最后分别对三点弯曲梁模型及有侧限压缩模型进行了数值计算.对三点弯曲梁计算了不同温度下冻土破坏过程曲线,给出了不同土质非线性破坏特征值-临界张开位移值,并与实测值进行比较,二者相符;对压缩模型,给出了裂纹张开位移过程曲线和不同土质张开位移临界值,并与理论预测值进行了比较,二者也基本相符.在计算方法上采用了有限元和解析法相结合的半解析有限元法.

Numerical simulation of nonlinear fracture failure process of frozen soil

Since the frozen soil has nonlinear character, its fracture failure process is nonlinearity and there exists the crack damage zone (MDZ). Simplifing MDZ as fictitious crack and assuming that there is cementation force on the crack face, the frozen soil cementation force crack model of nonlinear fracture failure is presented. According to the Paris displacement formula, the expressions of crack tip open displacement specially for three-points bend beam (3PBB) model and compression model of frozen soil are proposed under the loading of nonlinear cementation force on the crack face, besides some parameters are provided for calculating the nonlinear failure process of the frozen soil. Finally the numerical simulation of 3PBB model and compression model of frozen soil is presented. Semi-analytical finite element method is adopted in the numerical simulation. For 3PBB model, the failure process curve at different temperature and crack tip open displacement (CTOD) critical value for different types of frozen soil are given. For compression model, the relation curve CTOD vs. loading and CTOD critical value for different types of frozen soil are given, too. Compared with the experimental value in the frozen soil experiment, the result values accord well.