Abstract: 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.

Key words: fractured rock mass under low temperature, hydro-thermal coupling, fracture seepage, water/ice phase transition, artificial freezing method