A fully coupled thermo-hydro-mechanical model including the determination of coupling parameters for freezing rock

The freeze-thaw damage of rock is mainly induced by cycling loading of pore ice pressure and thermal stress under coupled thermo-hydro-mechanical (THM) condition at low temperature. The accuracy and correctness of coupled T-H-M model for freezing rock are controlled by critical parameters including unfrozen water content, ice pressure, permeability, and the equivalent thermal conductivity. The difference of THM coupling process between freezing rock and freezing soil is the evolution rule of those critical parameters, which change drastically with freezing temperature. The permeability is related to the unfrozen water content and high enough to be considered at the temperature above -5 degrees C. Combining numerical experiment with mixture theory, the equivalent thermal conductivity of freezing rock is also studied which is proved to be well expressed by exponential weighted mean model. Then the governing equations for THM coupling of freezing rock under low temperature are deduced based on energy conservation law, mass conservation law and the principle of static equilibrium considering water/ice phase transition. Those equations include the effects of seepage velocity and latent heat of phase transition on heat transfer, the influences of segragation potential and volume strain on water flow, and the impacts of temperature and pore water/ice pressure on frost heaving strain. Compared with a famous coupled THM laboratory test conducted by Neaupane and Yamabe, the proposed THM model has a good prediction of heat conductivity and frost heaving strain for freezing rock.