Abstract: Pressure-bearing and concealed karst caves intensively develop in karst areas. A three dimensional test system was developed to study the evolution process and mechanism of water inrush disaster. In addition, new similar materials were developed for fluid-solid coupling test, and innovative preparation methods were proposed for pressure-bearing karst caves. Various tests under different scenarios were carried out with different tunnel excavation schemes and different cave sizes based on the background of Qiyueshan tunnel on Lichuan-Wanzhou expressway. Multivariate parameters (such as displacement, stress and water pressure) were monitored to forecast water inrush. Test results show that water inrush disaster easily occurred under adverse impacts (blasting disturbance and pressure-bearing and concealed karst caves). Firstly, fractures developed intensively under blasting excavation, and displacement was 27% higher than the artificial excavation in the key monitoring position. In addition, the rate of stress relieving reached 23.5%, and the seepage pressure was only 36.7% of the initial pressure. The water inrush occurred when the pressure was maintained at 40 kPa for fifteen minutes. In the same hydraulic loading conditions, the greater the karst cave size, the greater the displacement release rate, but the lower the seepage pressure. Finally, a larger karst cave caused water inrush earlier under the action of stress and seepage. The catastrophic process was divided into three stages: group cracks initiation, the formation of preferential transfixion passageway and complete damage of water insulation rock.

Key words: karst tunnel, surrounding rock of water insulation, water-inrush evolution, blasting disturbance, fracture failure