Abstract: To reveal the bearing characteristics of surrounding rock mass of hydraulic tunnels under the combined effects of high geotemperature and high internal water pressure, this study conducts experimental tests on a large-scale structural model of a hydraulic pressure tunnel with large geotemperature gradients in multi-physical fields through developing a similar material of complete hard rock mass. For the tests, we adopt acoustic emission techniques for signal monitoring and locating, develop a new loading technique of combined temperature loads and internal water pressure, and analyze the dynamic evolution processes of temperature field, pore pressure field, acoustic emission, and fracture propagation. Results show that compared to the condition without high geotemperature, the critical internal water pressure of the surrounding rock mass of the tunnel at the start of hydraulic fracturing is lowered obviously. In a high geotemperature environment, the induced cracks between the main fractures in the rock mass have evolved quite completely, manifesting the difference from the normal geotemperature cases where only a few main fractures are mobilized. And the rock mass has undergone an obvious coupling effect of thermo-hydro-mechanical fields, and the fracture propagation and increasing damage of the rock mass are featured with discontinued step evolution under constant water pressure. Under high in-situ stress conditions, the locations of hydraulic fractures and fracture propagation are influenced significantly by the lateral confining coefficient of in-situ stress.

Key words: hydraulic tunnel, structural model test, high geotemperature, high water pressure, thermo-hydro-mechanical coupling