FAILURE MODES, CHARACTERISTICS AND EARLY WARNING IDENTIFICATION OF ROCK MASS RESISTING WATER GUSHING-OUT IN TUNNEL

As a kind of geological disaster, water gushing-out is more common in the construction of karst tunnels, and the structural type, failure mode of the rock mass resisting water gushing-out is closely related to the occurrence of such disaster. Through the statistical analysis on 30 cases of water gushing-out accidents, it was found that the water gushing-out disaster mainly occurred in the deep-long and long-span karst tunnel, and the discharge of water was about 100 to 10 000 m³/h. Based on the detail description of the rock mass resisting water gushing-out structure in the cases, six structural types were summerized, including intact to relatively intact structure, layered fragmented structure, block fractured structure, intermittent structure, soil-rock mixture structure and dense bulk structure. The failure mode of each rock mass structure was described in detail. Then, the permeability characteristics of three representative types of rock mass resisting water gushing-out under high water pressure were described. It was known that the formation of water gushing-out channel was a gradual process in which the internal joint and fissure expanded, penetrated and scoured under the repeated action of high water pressure. Finally, in order to predict the possibility of water gushing-out, the magnitude and trend of water gushing-pressure, displacement change during deformation and failure of the rock mass resisting water gushing-out and variation of temperature field of rock mass affected by groundwater were distinguished and analyzed. They were used as early warning identification of water gushing-out disaster, and the measures were taken to control the disaster before water gushing-out happened.