To reveal the mechanical behavior characteristics of surrounding rock of hydraulic tunnels under high temperature and hydraulic pressure conditions

this paper proposes a coupled thermo-hydro-mechanical-damage (THMD) model which considers change of hard rock strength parameters involving damage evolution based on multi-field coupling theory with permeability coefficient and heat transfer coefficient varying with rock damage. The implementation of THMD numerical simulation is conducted by the FLAC3D software. The model is proved to be feasible by validation of a physical modeling test

and then the THMD model is employed to deduce the evolution process of multi-field coupling of hydraulic tunnels with high temperature and hydraulic pressure. The evolution process is used to analyze the load-bearing characteristics influenced by different factors. The multi-field coupling effects are very significant in hydraulic tunnels with high temperature and hydraulic pressure after water-filling operation. The complex tensile stress generated by combined load of high temperature gradient and hydraulic pressure contributes to adverse impacts on safe performance of surrounding rock. The damage and crack depth of surrounding rock are larger if the temperature gradient

hydraulic pressure and thermal expansion coefficient are larger. If the lateral pressure coefficient is close to 1

more cracks around the tunnel with random directions tend to form. If the lateral pressure coefficient is less than 1/3

fewer cracks appear around the tunnel and the directions of the cracks are mostly parallel to the direction of the maximum initial stress. The general bolt-shotcrete support does not have good performance in reinforcement of hydraulic tunnels.