Experimental investigation on the hydraulic characteristics of water inrush in deep buried filled karst conduit considering the permeability

Abstract

Water inrush in karst areas is a challenge for the safe construction of deep-buried tunnels due to complicated hydrogeological environments, especially encounters with karst structures that are filled with water and sediments. To study the hydraulic characteristics and disaster evolution of filling materials in complex filled karst conduit during water inrush, large-scale model experiments of seepage and water inrush of filling materials with different permeabilities in karst conduit were conducted according to the engineering geological background of the Qiyueshan tunnel. The whole process of initial seepage and water inrush caused by excavation under the conditions of high ground stress and high confined water pressure is presented, and the spatio-temporal evolution characteristics of pore water pressure inside karst fillings were deeply analyzed. The results show that the pore water pressure in karst fillings generally increases with time while decreasing with the seepage path at the initial seepage stage, and it could be divided into the discontinuous stage, nonlinear stage, and linear stage along the seepage path over seepage time. Additionally, there are undisturbed area, disturbed area, and water inrush of filling materials in karst conduit at the excavation stage. The permeability of karst fillings has an obvious impact on the development process of pore water pressure, as well as the zone and degree of excavation disturbance. The adjacent hydraulic gradient could more accurately reflect the hydraulic characteristics of the karst fillings along the seepage path than the average hydraulic gradient, and make it possible to observe the formation process of seepage channels. The karst fillings with higher permeability has a looser structure and higher porosity, which would form more potential seepage channels at the seepage stage and be more affected by excavation disturbance. Therefore, it is easier to develop into the dominant seepage channels and result in water inrush. Research results may provide reasonable guidance for water inrush prevention and reduce disaster consequences during tunneling in karst areas.