Prediction of Transient Rockburst under Coupled Thermo-mechanical Effects Considering Vertical Geothermal Stress

The hydraulic fracturing method is a single mean for measuring the in-situ stress during the geological exploration stage of tunnels. Limited by the failure of the hydraulic fracturing method to consider the geothermal stress and the use of a steady-state method for rockburst prediction, the traditional rockburst prediction method will weaken high ground temperature rockburst intensity. Based on geological survey data, a three-dimensional numerical model was established for the tunnel site of the area of Kangding. After removing the geothermal stress from the horizontal principal stress ， the in-situ stress inversion was carried out. Then, the in-situ stress field was obtained by superimposing the geothermal stress on each inversion stress component, which was used as the stress boundary condition of the rockburst prediction model. Considering the convective heat transfer process between the tunnel wall and the environment inside the tunnel and the thermal stress peak effect at the moment of excavation comprehensively, the coupled thermo-mechanical module of Cortisol software was used to solve the tunnel wall stress in a transient state, to obtain the revised rockburst intensity index. On this basis ， an analysis was conducted on the difference between the traditional rockburst prediction method and steady-state and transient solution methods that consider geothermal stress. The results show that the geothermal stress of the tunnel accounts for about 20. 1% of the horizontal principal stress and about 20. 5% of the vertical stress. Ignoring the existence of geothermal stress will weaken the intensity of rockburst prediction. Compared with the traditional rockburst prediction method, the steady-state rockburst prediction intensity that considers geothermal stress is increased by about 2% ，while the transient rockburst prediction intensity that considers geothermal stress continues to increase by about 14.2%. Therefore, the rockburst prediction of high-temperature tunnels must fully consider the superposition effect of geothermal stress and solve it by transient state. © 2023 Science Press. All rights reserved.