Research On Mechanical Behavior And Stability Of Anti-dip Rock Slope In The Whole Process Of Flexible Flexural Toppling

The toppling deformation of anti-dip layered slope is widely exposed in the slopes of water hydropower,mines and roads,which has an important impact on the safety of the projects.The deformation evolution stage and mechanical state of the anti-dip rock slope are the key to the stability evaluation and the selection of the treatment scheme.The toppling deformation is not only controlled by the structural surface of slope but also by the characteristics of rock mass(such as section size and mechanical properties of rock mass,etc.).There are still some shortcomings in the periodic mechanical characteristics of the flexible flexural toppling deformation process,especially the stress behavior and deformation characteristics between layers in the whole process of deformation are seldom studied.In this paper,the basic characteristics and main forming conditions of the flexible flexural toppling deformation of the anti-dip rock slope are summarized on the basis of consulting a large number of cases of the flexible flexural toppling and analyzing a large number of field data.The sensitivity of forming conditions,mechanism and process of toppling failure,characteristics of interlayer mechanical behavior and criterion of toppling failure of flexible flexural toppling deformation have been systematically studied by using a variety of research methods.The whole process curve of flexible flexural toppling deformation is presented,and the periodic mechanical criterion and the stability evaluation method are established.The main results obtained through systematic research are as follows:(1)The characteristics of "flexibility" of rock strata,small thickness of single layer and steep slope are the necessary conditions for the occurrence of flexible flexural toppling deformation.The occurrence conditions respectively reflect the development characteristics of mechanical properties of rock mass,thickness of rock layer and dip angle of rock strata.(2)In combination with the existing studies,relevant indexes such as the toppled angle,maximum tension tensor,unit tension tensor,longitudinal wave velocity and the characteristics of deformation and fracture were selected to study the engineering geological zone of flexible flexural toppling deformation,and the mechanical mechanism of deformation and fracture of rock mass in each zone was summarized.(3)Numerical simulation method was used to select the toppled slope in front of Miaowei hydropower station.After the reasonability of the model was verified by inversion analysis,the sensitivity of the flexible flexural toppling deformation was analyzed by comparing and analyzing the displacement deformation before and after the change of single factor conditions.The results show that slope height,slope angle and mechanical properties of rock mass(the angle of internal friction between rock mass and structural plane)have significant influence on the flexible flexural toppling deformation,followed by the dip angle of rock strata.(4)Centrifugal model test was used to study the whole process of the failure of flexible flexural toppling deformation under different air conditions.The experimental results show that the failure mechanism is as follows: toppling bending of rock strata,formation of multistage toppling bending surface(zone),formation of penetrating toppling bending surface(zone),and shear failure of rock mass along a certain level of penetrating toppling bending surface(zone).(5)The typical rock mechanics parameter set(20MPa)was selected to carry out the research on the numerical calculation model of the flexible flexural toppling,and the displacement curve characteristics of the monitoring point of the numerical calculation model and the failure characteristics of the flexible flexural toppling were comprehensively analyzed,and the whole process deformation curve of the flexible flexural toppling failure was proposed.The monitoring displacement curves show that the whole process of flexible flexural toppling deformation can be divided into start-up stage,rapid development stage,temporary stability stage,creep stage and failure stage.Through mechanical analysis,the mechanical criterion of each stage was established by selecting slope angle(?),dip angle(?)and angle between rock strata and slope surface(?).(6)The stress and displacement curves of the monitoring layer of the numerical calculation model reveal the distribution law of interlayer forces and the development law of interlayer dislocation in the development process of topplling deformation.In the starting stage,the normal stress and shear stress are almost full-length distributed,and the stress is not triangular in a regular distribution along the depth of the structural plane,but the resultant force is approximately equal to the length integral of the triangular distribution of the structural plane.With the development of the flexible flexural toppling deformation,the length of the structural plane in which the layers are involved decreases gradually.On the whole,the stress value in the slip zone at the foot of slope is the largest,the stress value in the toppling affected zone is the smallest,and the stress value in the toppling zone is the mediate.The interlayer displacement law shows that the shear displacement is much larger than the normal displacement,and the maximum occurs at the top of the rock layer or the position of " gap" between layers.(7)A three-dimensional mechanical model of toppling deformation is established by introducing the lateral constraint coefficient and the lateral dimension of the slab beam section,and the quantitative relationship between the toppling fracture depth and the lateral constraint coefficient and the width of the slab beam is determined.The first breaking depth of the plate beam increases with the decrease of the lateral constraint coefficient of the plate beam,which indicates that the smaller the lateral constraint coefficient is,the better the air condition is,and the more prone the toppling failure is,and the greater the toppling failure depth is,the boundary effect of toppling deformation failure is revealed.(8)Based on the spatio-temporal effect characteristics of the development process of flexible bending topplling,a whole-process evaluation method of the deformation stability of flexible bending topplling is proposed,which is "shallow and initial stage + deep and final stage".The stability of the initial stage of shallow rock mass is improved by the cantilever beam method.The stability of the final stage of deep rock mass is based on the abrupt transition theory of the final form deformation of rock layer.The method is applied to a toppled case,and the results show that the analysis results are in good agreement with the results of field investigation.