低温裂隙岩体水-热耦合模型研究及数值分析

裂隙渗流会引起裂隙周围岩体中的温度场变化，在低温岩体中其影响更为明显；此外，裂隙水与周围低温岩石介质发生热交换会引起裂隙中的水冰相变过程发生，而裂隙水冻结将阻碍裂隙渗流，引起裂隙渗流场的变化。因此，低温下的裂隙岩体水-热相互作用是一个强耦合过程。考虑裂隙中的水冰相变过程和渗流作用，建立了低温冻结条件下裂隙岩体水-热耦合模型；以冻结法施工为例，考察了低温冻结过程中裂隙水渗流对裂隙冻结交圈的影响。研究结果表明：由于裂隙渗流的存在，距裂隙较远处岩石先冻结，裂隙冻结所需时间远大于周围岩石；裂隙宽度和裂隙水压力差都会影响冻结交圈时间，裂隙越宽、水压力差越大，裂隙冻结需要时间越长；随着冻结时间的推进，裂隙水渗流速度逐渐降低，当裂隙冻结后裂隙渗流停止。最后通过构建随机裂隙网络模型，利用所建立的水-热耦合模型考察了裂隙网络渗流对冻结交圈的影响，说明了在冻结法施工中考虑裂隙的重要性。

A coupled hydro-thermal model of fractured rock mass under low temperature and its numerical analysis

Fracture seepage can result in a change of temperature fields of rock around cracks, which is more apparent in particular under low temperature. In addition, heat exchange between fracture water and the cold rock medium may induce water/ice phase transition in fractures. The generation of solid ice prevents water from flowing in fractures, which leads to a change of the seepage field of fractured rock mass. Thus, this hydro-thermal coupling action of fractured rock mass under low temperature is extreme. By considering water/ice phase transition and fracture seepage, a coupled hydro-thermal model is developed for fractured rock mass under low temperature. To illustrate the influence of fracture flow on the freezing process, an example of the artificial freezing method is investigated. The results show that the rock medium far from fractures is frozen earlier for fracture flow and the completed freezing time of seepage fractures are more than that of rock medium. Both the fracture width and delivery head of fracture water affect completed freezing time. The completed freezing time increases with the increase of fracture width and delivery head of fracture water. The seepage velocity in fracture gradually decreases along with freezing time, and the fracture seepage stops after fracture water is frozen. Finally, by building a stochastic fracture network model, the impact of seepage in fracture network on the freezing process is studied using the proposed coupled hydro-thermal model. The calculated results indicate the significance of considering fracture seepage during artificial ground freezing.