Numerical Simulation Of Centrifugal Model Test For Toppling Deformation Of Layered Anaclinal Slope

Toppling is the uppermost failure pattern of anaclinal rock slopes.In western China,many large-scale deep-seated toppling deformations of high anaclinal slopes on a side of deeply incised valley have been observed.The maximum horizontal toppling depth is even more than 300 m.However,the research on the mechanism of toppling deformation of anaclinal slope is still not perfect,especially for the soft-hard interbedded anaclinal slope.In this paper,anaclinal slope was taken as the main research object.Firstly,50 examples of toppling deformation were analyzed through field investigation and data collation.The distribution and developmental characteristics of toppling deformations were preliminarily explored.By means of large centrifugal model test and discrete element numerical simulation,the mechanism and influencing factors of toppling deformation of anaclinal layered slope were systematically studied.The main contents and achievements of this paper are as follows:(1)Through field investigation,data collation and induction analysis of 50 examples,the geographical distribution and developmental characteristics of toppling deformations were clarified,and the relationship between the intensity of toppling and structural factors,such as slope height,slope angle and dip angle,was analyzed.Statistics showed that the toppling deformations were widely distributed in the southeastern margin of the QinghaiTibet Plateau,usually along rivers and on one side of the longitudinal V-shaped valley.The slope height of most toppling deformations was 300-600 m,and the lithology were soft-hard interbedded.Most toppling slopes were convex slope.When the slope gradient was 40 degrees,the dip angle was 80 degrees and the slope height was 400 m or so,it is the most disadvantageous to the stability of anaclinal slopes.(2)Based on the centrifugal model test of single lithologic layered anaclinal slope,the discrete element numerical simulation was carried out.The mechanism of collapse deformation and the influence law of slope angle,dip angle and material parameters were further clarified.Deformation of anaclinal slope can be divided into three stages: elasticity,plasticity and failure.Only when the combination of slope gradient and dip angle satisfied some certain conditions can the toppling deformation occur.The final fracture surface is approximately a straight line and intersected with the normal plane of strata in a small angle.Using single factor analysis method,it was easiest to toppling when the dip angle was 60 ?80°.(3)Through centrifugal model test,the toppling mechanism of soft-hard interbedded anaclinal slope was studied.It was concluded that the slope was damaged at about 40 g,and the failure surface was curved,which is obviously different from that of single lithologic slope.(4)Based on the principle of orthogonal design,the centrifugal model test of soft-hard interbedded slopes was extended by discrete element numerical simulation.It was revealed of the influence of slope morphological and structural characteristics,soft-hard rock parameter ratio and mechanics parameters of bedding planes on the stability of anaclinal slopes.The results show that the influence of slope shape and structure factors from large to small was slope gradient,slope height,slope shape,dip angle,thickness ratio and thickness.From large to small,the influence of parameters ratio of hard rock and soft rock is block density ratio,bulk modulus ratio,friction angle ratio,shear modulus ratio,tensile strength ratio and cohesion ratio.The influence of the mechanical parameters of the bedding planes from large to small is angle of internal friction,cohesion,bulk modulus and shear modulus.(5)Based on the analysis of displacement monitoring curve,normal stress distribution of bedding planes and stress characteristics of anchor cables,the monitoring and early warning scheme of anaclinal slope was discussed.And a method for predicting the location of fracture surface was proposed.It was revealed that the normal stress of the bedding plane had obvious abrupt change near the fracture surface.And it was found that the connection of the maximum axle force point of each anchor cable was just the most likely location of the fracture surface to bend and break.