冻融循环作用下炭质页岩蠕变模型研究

冻融循环作用下炭质页岩蠕变是高速公路高陡边坡稳定性研究的热点问题之一。为揭示冻融循环作用下炭质页岩的蠕变特性，将炭质页岩试样分别进行0次、5次、15次、25次冻融循环，在围压为4 MPa条件下，采用分级增量加载方式对试样进行三轴压缩蠕变试验，试验发现冻融作用下炭质页岩蠕变具有明显的非线性特征，轴向应变随冻融循环次数、应力水平和时间增加而增大；根据蠕变曲线特征，将蠕变曲线分为2个阶段，即稳定蠕变阶段和不稳定蠕变阶段；利用损伤定义及Lemaitre应变等效方程，建立稳定蠕变阶段的冻融损伤演化方程；基于损伤力学和概率统计理论，采用Von-misses屈服准则，建立不稳定蠕变阶段的冻融和蠕变耦合损伤方程；通过引入冻融和蠕变损伤变量对Burgers模型参数进行修正，建立冻融作用下的蠕变损伤模型。研究表明：岩石损伤随冻融循环次数增加而增大，但损伤增加速率减小，最终趋于稳定；冻融和蠕变耦合作用下，冻融作用使得岩石损伤累积，会加快岩石的蠕变破坏；分段建立的损伤方程能较好地揭示岩石损伤随冻融循环次数、应力水平和时间增加的变化规律；改进的蠕变模型与试验曲线拟合度较好，且参数物理意义明确。研究成果能为炭质页岩高陡边坡稳定性分析提供理论参考。

Research on Creep Model of Carbonaceous Shale Under Freeze-thaw Cycle

The creep of carbonaceous shale under the freeze-thaw cycle is one of the hot issues in the study of the stability of high and steep expressway slopes. To reveal the creep characteristics of carbonaceous shale under freeze-thaw, carbonaceous shale samples were subjected to 0/5/15/25 freeze-thaw cycles, respectively. Then, under a confining pressure of 4 MPa, triaxial compression creep tests were carried out on the samples by means of stepwise incremental loading. It was found that the creep behavior of carbonaceous shale under freezing and thawing has obvious nonlinear characteristics. Axial strain increases with the number of freeze-thaw cycles, stress level, and time. According to its characteristics, the creep curve is divided into two stages:a stable creep stage and an unstable creep stage. Using the damage definition and the Lemaitre strain equivalent equation, the evolution equation of freeze-thaw damage in the stable creep stage was established. Based on damage mechanics and probability statistics theory, the coupling damage equation of freeze-thaw and creep in the unstable creep stage was established using the von Mises yield criterion. The parameters of the Burgers creep model were modified by introducing freeze-thaw and creep damage variables, and the creep damage model under freezing and thawing was established. The results showed that the damage of the rock increases with the number of freeze-thaw cycles, but the rate of damage increase decreases and then finally becomes stable. Under the coupled effect of freeze-thaw and creep, freezing and thawing cause rock damage to accumulate, which promotes creep failure of the rock. The damage equation established by segmentation can well reveal the variation of rock damage with the number of freeze-thaw cycles, stress level, and time. The improved creep model has a good degree of fit with the experimental curve, and the physical meaning of the parameters is clear, which proves the rationality of the creep model. The results provide a theoretical reference for stability analysis of carbonaceous shale in high and steep slopes.