Model tests and numerical analysis for water inrush caused by karst caves filled with confined water in tunnels

To study the stability of the surrounding rock of concealed karst caves under different filling water pressures and to reveal the water inrush mechanism, a self-developed new type of model test system is applied to the solid-fluid coupling model tests on lagging water-inrush of karst cave, and the variation of the multi-field information such as displacement, stress and seepage pressure is effectively revealed. The advantages of numerical analysis are used to carry out fluid-solid coupling numerical simulation of tunnel excavation process under different filling water pressures (0.4 to 1.1 MPa). Based on the results of model tests and numerical simulations, the karst cave has impact on the surrounding rock within the scope of one time the cave diameter. The stress level, stress release rate and dissipation rate of pore water pressure of the ordinary surrounding rock are higher than those of water-resisting rock mass. Among them, the displacement exhibits an obvious stable stage. In the course of excavation, the rate of stress relieving gradually decreases when the filling pressure increases. Moreover, the osmotic pressure increases as a whole, but the gradient decreases. Nevertheless, after the karst water pressure reaches 0.8 MPa, obvious change starts to appear. The process of water inrush is truly reproduced at the hydraulic loading stage. The test results are used to guide the design and construction of the similar projects.