Determination of required rock thickness to resist water and mud inrush from karst caves under earthquake action

Two types of filled karst caves, with water and with water-mud mixture, in front of the tunnel face are studied, to estimate the required thickness of supporting rock stratum in order to prevent water and mud inrush under earthquake action. Generalized models and computational techniques are developed for such conditions. The models consider the shear and bending failures of the supporting rock stratum against the pressure from filling materials in the caves. Combined with pseudo-static and dynamic theories, computational models are developed to estimate the minimum thickness of the rock stratum between the face and the cave. The factors governing the minimum thickness of the supporting rock stratum to resist water and mud inrush from the caves are analyzed. Finally, the theoretical models and computational methods are verified with case studies. The studies show that: (i) Under earthquake action, the required rock stratum thickness shows an accelerated increase trend with the increasing earthquake intensity; (ii) Failure of the supporting rock stratum under the pressure from the filling material in the cave is likely due to bending; (iii) The minimum thickness of the rock stratum increases with tunnel depth, tunnel height and karst water pressure, while it decreases with increasing shear strength indexes of the filling material and surrounding rock quality.