Research on the Mechanism and Safe Thickness of Karst Tunnel-Induced Water Inrush under the Coupling Action of Blasting Load and Water Pressure

Abstract

When the drilling and blasting method is used to construct a tunnel through the karst stratum, the coupling effect of the blasting load and the karst water pressure in front of the tunnel face exposes the tunnel face to the risk of water inrush, which threatens the safety of personnel and property. It is very important for the design and construction of related tunnels to study the evolution mechanism of water inrush in karst tunnels and determine the minimum thickness of outburst prevention under blasting. Relying on the Dejiang tunnel Project in Tongren City, this paper adopts the Smoothed Particle Hydrodynamic–Finite Element Method (SPH-FEM) coupling calculation method to study the evolution process of water inrush in karst tunnels under blasting, analyzing the results of water inrush in tunnels under different rock wall thicknesses under blasting. Then, according to the regression of rock wall stress peak data, the analysis determines the minimum outburst prevention thickness of the karst tunnel. The research results show that there is a superposition effect between the blasting stress wave and the gravitational interaction of the karst water itself, and that the Smoothed Particle Hydrodynamic (SPH) particles in the aquifer cause damage and cracks to the rock wall under the coupling action of the blasting load and the karst water pressure, further leading to the expansion of the cracks and the formation of inrush channels. the stress, vibration velocity, and displacement of the unit at the junction of the aquifer and the rock layer show a trend that first decreases, then increases, and then decreases with an increase in the thickness of the rock wall. Based on the actual geological conditions of the Dejiang tunnel project parameters, when the thickness of the rock wall is 3.08 m, the peak stress of the rock formation unit at the junction with the aquifer reaches the maximum value. In order to avoid water inrush during blasting, the minimum outburst prevention thickness should be greater than 3.08 m. Based on the analysis results, a corresponding water inrush prevention plan was formulated on site which effectively guaranteed construction safety and, at the same time, verified the reliability of the analysis results. The relevant research results can provide useful references for similar projects.