Analysis of the thickness of the outburst prevention layer in karst tunnels under the control of compressive faults

Abstract

In order to solve the problem of the safe thickness between concealed karst caves and tunnels under the influence of compressive faults, a simplified calculation model of the safe thickness under three working conditions is constructed. Based on the cusp catastrophe theory, the analytical formulas of the safe thickness between concealed karst cave and tunnel are derived. On this basis, based on the finite difference method, the evolution law of the maximum displacement of rock slabs under different cave water pressures is revealed, the criterion of “when the maximum displacement of the rock slab exceeds the thickness of the rock slab, the water inrush caused by the strength failure of the rock slab occurs in the tunnel” has been established, and the rationality and effectiveness of this criterion have been verified. When the compressive fault is located in the middle of the rock slab, the difference between the theoretical thickness of the rock slab and the maximum displacement of the rock slab is only 0.26 m, the simplified model can accurately determine the thickness of the anti-outburst rock slab. When the compressive fault is located in a quarter of the length of the rock slab, the simplified model also has strong applicability. Research has shown that when the cave water pressure is small, the rock slab displacement increases approximately linearly with the increase of cave water pressure; When the water pressure increases to a certain extent, the cave water pressure and rock slab displacement show a nonlinear correlation, and the rock slab deformation enters the plastic stage; The spatial location of faults has a significant impact on the applicability of analytical formulas, when the fault is located in the middle of the rock slab, the influence of the deformation of the fault itself on the stability of the rock slab should be considered; For the working condition where the karst cave above the tunnel, the theoretical thickness of the rock slab has a certain linear relationship with the length of the rock beam, the corresponding theoretical thickness of the rock slab when the fault is located at other locations can be determined according to the linear relationship; When the location of the fault moves from the middle of the anti-outburst rock slab to the root of the anti-outburst rock slab, for working condition three, the theoretical safety thickness required for the fault located in the upper part of the rock slab is slightly greater than that required for the symmetric position. The research methods and results of this paper have certain reference and application value for similar research and engineering problems.