高温冻土融化固结的水热力耦合模型构建

依据比奥(Biot)固结理论,应用总拉格朗日(Total Lagrangian)方法建立考虑大变形的应力场控制方程;引入应力-温度耦合损伤模型作为冻结状态下的高温冻土本构模型,以未冻水含量为耦合节点建立水热力耦合模型;通过冻结粉质黏土的升温三轴压缩试验验证模型的有效性,分析水热力耦合模型与应用小应变假设的模型的差异。结果表明:水热力耦合模型经过引入高温冻土应力-温度耦合损伤本构模型,冻结状态初始融化阶段预测结果与试验曲线较吻合。在变形加速至缓慢变形过渡阶段(1.5~2.5 h),模拟结果与试验曲线存在一定差异,但整体可有效预测高温冻结粉质黏土的融化固结过程。考虑大应变状态的水热力耦合模型,对融化变形的预测精度优于应用小应变假设的模型。根据模拟结果,分析水热力三场的相互作用关系、冻土融化固结过程,高温冻土外部升温状态下,边缘融化部分形成排水通道,加速上部土体水分排出。

Construction of Thermo-hydro-mechanical Coupling Model for Thawing Consolidation of Warm Frozen Soil

With Biot’s consolidation theory, the governing equation of stress field considering large deformation was established by using Total Lagrangian method. The stress-temperature coupled damage model was introduced as the constitutive model of warm frozen soil under frozen state, and the water thermal coupling model was established with unfrozen water content as coupling node. The validity of the model is verified by the temperature rising triaxial compression test of frozen silty clay, and the difference between the thermo-hydro-mechanical coupling model and the model with small strain assumption was analyzed. By introducing the coupled stress-temperature damage constitutive model, the predicted results of the initial thawing stage of frozen state are in good agreement with the experimental curves. In the transition stage(1.5-2.5 h) from acceleration to slow deformation, the simulation results are different from the test curves, but the whole process can effectively predict the melting and consolidation process of warm frozen silty clay. The prediction accuracy of the model considering large strain state is better than that of the model with small strain assumption. According to the simulation results, the interaction between the three fields is analyzed. In the process of thawing and consolidation of frozen soil, when the external temperature of warm frozen soil rises, the edge melting part forms drainage channel, which accelerates the water discharge of upper soil.