Mechanism and stability of secondary toppling of counter-tilt rock slopes

Among kinds of toppling failures of anti-dipping rock slopes, the secondary toppling is the main inducement. The geo-mechanical model for the secondary toppling of the anti-dipping rock strata under the action of the soil behind the slope is established. Based on the laboratory physical simulation tests, the distribution laws of earth pressure on the surface, failure modes, shapes and positions of the integral failure surface of the counter-tilt rock strata are analyzed. According to the Coulomb's active earth pressure theory, the theoretical values of normal pressure at each point on the underlying stratum surface are basically consistent with the measured values, but the soil arching effect leads to the difference between them. With the increase of overlying soil thickness and surcharge effect, the soil arching effect becomes more obvious. The possible failure modes of various strata include bending failure, bending-slip failure and sliding failure. The integral failure surface of the underlying anti-dipping rock stratum is an approximate plane through the foot of the slope, and the angle between the integral failure surface and the normal direction of the rock strata is 0°~25°. Based on the superimposed cantilever beam model, the limit equilibrium analysis method of anti-dipping rock strata is improved by introducing the reduction coefficient of the cohesion of joints on the cross-section of rock strata and the tensile strength of rock with the embedded depth of rock strata. The theoretical formula of thrust for arbitrary stratum in the slope is derived. The safety factors of deformation and failure of arbitrary rock stratum and the comprehensive safety factor of the whole slope collapse are defined respectively. The theoretical method for calculating the potential integral failure surface of the underlying anti-dipping strata is proposed, and the sensitive factors affecting the location of the potential integral failure surface are found. © 2019, Science Press. All right reserved.