Analysis Method Of Failure Mechanism And Stability For The Secondary Toppling Of Jointed Rock Slope

Because of the special region and geological environment in Western China,where a large number of high and steep slopes are located,and slope failure is frequent,especially in the area where a large number of layered rock masses are distributed.In the usual understanding,the stability of the inclined slope is generally poor,while the stability of the anaclinal slope is relatively good.However,there are more and more cases of toppling deformation and failure of the anaclinal slope,which change this "general knowledge".And the failure of anaclinal slope are large landslides,huge losses caused by these disasters.This article is relied on the financial supports from the China National Science and Technology Support Program: Research on catastrophic mechanism and process control of typical high slope in Southwest Mountainous Areas(2015BAK09B01-2),and the special research projects of basic science and frontier technology in Chongqing: Catastrophe mechanism and dynamic stability evaluation method of typical jointed rock high slope in Three Gorges Reservoir Area(NO.cstc2015jcyjBX0139).Based on laboratory physical simulation experiment and theoretical analysis,a geomechanical model of secondary toppling failure of anaclinal rock slope is established,the formation process and catastrophic mechanism of anaclinal rock-soil composite slope are revealed,and the evaluation method for the overall stability of this kind of slope is proposed,and the comprehensive safety factor is defined.The main achievements of this study are as follows:(1)Aiming at the secondary toppling of anaclinal slope,the distribution law of earth pressure,failure mode and the shape and position of failure datum plane are revealed by physical model test.The theoretical value which is obtained from the theory of Coulomb active earth pressure,and the measured value of the normal pressure at each point on the underlying rock strata surface show linear growth,because of the effect of soil arching,their linear growth ratios are different.As the thickness of the overlying soil increases,the effect of soil arching becomes more obvious.The bending-dumping deformation and failure process of underlying soft rock does not depend only on the relationship between the maximum tensile stress and the tensile strength of rock layers,but also there are several points where the maximum tensile stress is greater than or equal to the tensile strength of rock layers.There are many cracks on the upper surface of each rock strata,and plastic bending occurs.Each rock strata interacts with each other to coordinate and balance.When the whole balance is unstable,the slope will be destroyed.Therefore,it is more reasonable to consider the interaction between the rock strata as distributed load.It is difficult to describe the distribution of internal forces between rock layers by a single function.The failure datum plane of the secondary toppling of jointed rock slope is a plane which passes through the foot of the slope,and there is a slight bending tendency at the top of the datum plane.The angle between the failure datum plane and the normal level of rock strata is 0°~25°.(2)By introducing the reduction coefficient of the cohesion for joint's face,and tensile strength for rock on the cross-section of the rock strata with the depth of the rock embedded,the mechanical behavior of the bending and toppling deformation of the inverted-dipping stratum are described by using the "superimposed cantilever beams" model,and the limit equilibrium analysis method of the inverted-dipping rock strata is improved.(3)Based on the rigid body equilibrium theory and the compatibility equation of deformation,with the spatial geometric relationship,introducing the coefficient of increased gravity,a method for estimating the stability safety factor of secondary toppling of anaclinal rock slope is proposed.According to the limit equilibrium theory,a geological and mechanical model of secondary toppling of an anaclinal rock slope under the action of soil thrust behind the slope is established.A theoretical formula for downward thrust of arbitrary rock strata is derived.The safety factor of deformation and failure of arbitrary rock strata and the comprehensive safety factor of toppling failure for the whole slope are defined.(4)A theoretical method for calculating the most dangerous datum plane of compound slopes with anaclinal rock strata is proposed.Based on the matlab program,the sensitive factors affecting the location of the most dangerous datum plane are determined,include: thickness of anaclinal strata(t),dip angle of rock strata(?),dip angle of slope surface(?),dip angle of groundwater level(?),cohesion between rock layers(c?),connectivity of joints on the cross-section of the rock strata(k),the reduction coefficient of the cohesion for joint's face,and tensile strength for rock on the cross-section of the rock strata with the depth of the rock embedded(?).(5)On the basis of the superimposed cantilever beam model and the superposition principle,the theoretical formulas of the corner function and deflection function for bending deformation of arbitrary rock strata in excavated anti-dip slope are derived.The influence of the geometry parameters,physical and mechanical parameters of anaclinal rock slope on the toppling deformation of rock strata are revealed.The horizontal displacement of the top on the slope increases with the increase of the dip angle.However,the vertical displacement of the top on the slope increases first and then decreases gradually,the turning point is ?=55°~70°.With the increase of rock thickness,the horizontal displacement of the top on the slope decreases gradually,but the rate of the decrease for horizontal displacement diminishs gradually,and finally tends to zero.When the thickness of rock is unchanged,the horizontal displacement of the top on the slope increases with the increase of the number of rock strata.When the height of the slope is less than 30 m,the horizontal displacement of the top on the slope increases rapidly with the increase of the height of the slope.Conversely,When the height of the slope is more than 30 m,the horizontal displacement of the top slope increases slowly with the increase of the slope height.With the increase of the dip angle of the cut slope,the degree of bending of rock strata increases,and the trend is slow first and then fast,the turning point is ? >70°.When the dip angle of groundwater level is less than 50°,the horizontal displacement of the top on the slope remains basically unchanged.When the dip angle of groundwater level increases gradually from 50° to 60°,the horizontal displacement of the top on the slope increases gradually,and the larger the height of slope body,the more obvious the horizontal displacement of slope top increases.The horizontal displacement of the top on the slope increases linearly with the increase of the load on the top of the slope.And when the height of the slope is bigger,the horizontal displacement of the top slope increases faster.