| The toppling deformation of anti-dip layered slope is widely exposed in the slopes of water resources,hydropower,mines and roads,which has an important impact on the safety of the project.The evolution of the deformation of the fracture surface directly affects the rationality of the stability evaluation method.At present,the research shows that the toppling deformation is not only controlled by the characteristics of rock mass(such as thickness,hardness and softness),but also by the special structural characteristics of slope controlled by structural plane.However,the research on the control effect of structural characteristics on deformation evolution is still insufficient.In this paper,based on the conceptual model of geological formation and evolution,a deep and systematic study on the control effect of toppling deformation structural plane is carried out from many examples of anti-slope engineering.And laboratory tests are used to analyze the effect of cracks on rock mass characteristics,bottom friction tests are used to compare and study the control effect of cracks at different angles on fracture surface morphology.Physical centrifugal model tests are used to verify the deformation and failure characteristics,strain evolution rules and cracks under the control of such structures.The law of crack penetration failure and the characteristics of fracture surface formation and evolution reveal the whole process of deformation and failure evolution,crack propagation mode,mechanical mechanism and deformation and failure after crack formation and penetration.Accordingly,the main achievements of this paper are as follows:(1)Based on the statistical analysis of 58 major engineering anti-dip layered slopes,the controlling factors of deformation and failure are summarized.Uniform experiments based on UDEC simulation were designed and the results were analyzed by linear regression.From the regression equation coefficient relationship,it can be seen that the influencing factors of controlling factors are rock thickness(coefficient 4.9199),rock modulus(coefficient 0.8677),rock dip(coefficient 0.2783),slope angle(coefficient 0.1636).(2)Contribution rate method is used to analyze the sensitivity of influence factors for 33 anti-dip layered slope deformed bodies controlled by structures.The results show that the weight of fracture density factor is 0.269,which has the greatest influence on the development of toppling deformation,followed by slope gradient(weight is 0.162),slope shape(weight is 0.161)and lithology(0.158).The sensitivity of slope height and dip angle of rock strata is relatively low.The law shows that the occurrence of fractures has a significant influence on the toppling deformation of rock slope.(3)Engineering geological analysis of crack structure characteristics of four typical toppling deformed bodies.The results show that the steep and gentle double-fissure structure in the anti-dip stratified slope plays an obvious role in promoting and controlling the development and evolution process of the collapse deformation and failure,and the geological model of the anti-dip stratified slope is established according to the development characteristics of the fracture structure plane.(4)Based on the study of the geological prototype and the characteristics of tension,bending and failure of toppled rock mass,the mechanical test of rock splitting with cracks and anti-dip layered slope under mesoscopic conditions is designed.The results show that the tensile stress-strain curves of rocks with fissures can be divided into three stages:weak elastic(OA),strong plastic(AB)and strong elastic-plastic(BC);the angle of fissures has a significant influence on the strain and peak strain of weak elastic rock;the tensile strength of rocks is the smallest when the inclination of steep fissures is 80 degrees,while the tensile strength of rocks is the smallest when the steep fissures are fixed.Degree increases with the increase of dip angle of slow fissure;the change of angle of slow fissure affects the mode of rock splitting failure,while the change of angle of steep fissure affects the mode of crack initiation;the constitutive model of rock tensile stress and strain based on variable fractional calculus is obtained.?The OA segment can be expressed as:?/E(OA)=(??1)?1?1-?1/?(2-?1);?The AB segment can be expressed as:?/E(OB)=?/E(OA)+(??2)?2?1-?2-?1-?21/?(2-?2);?The BC segment can be expressed as:?/E(OC)=?/E(OB)+(??3)?3?1-?3-?1-?32/?(2-?3)?(5)9 groups of bottom friction tests were designed to compare three types of tests including no crack,one group of steep cracks and one group of steep and slow cracks,and to study the effect of different fracture angles on fracture surface.The test reveals that the change of dip angle of steep dip fissure has obvious regular influence on the deformation of rock slope and the shape of main fracture surface.The bigger the dip angle of steep dip fissure is,the shallower the initial part of collapse failure is,the smaller the area of collapse is,and the fracture surface gradually changes from near straight line to near arc;the occurrence of gentle dip fissure makes the crack of steep dip fissure grow along the tip,and communicates with each other to form a penetrating fracture.The surface process is faster;when the overlying layered rock mass on the main fracture surface is deformed by toppling,reverse bending and fracture will occur in its parts;through quantitative analysis,it is concluded that with the increase of the dip angle of steep cracks,the collapse deformation and failure amplitude decrease,and the fractal dimension value of the main fracture surface,whether in length or reflecting the complexity of the trace,also decreases.(6)Large-scale centrifugal tests on deformation evolution of anti-dip stratified slope show that the results are satisfactory.?From the analysis of displacement vector field and earth pressure data,it can be seen that the overall deformation of slope shows the characteristics of "reverse bending" macroscopically.?Through the longitudinal full-time strain analysis,it can be seen that the deep rock mass is in the state of reverse bending,and the deep rock mass is gradually transformed from the initial reverse bending state to the overturning bending state,and the front edge is "bulging" to the empty surface due to the fracturing and tension.?Through the analysis of the strain time history law of each loading stage,it can be seen that the top of the slope is in the state of overturning force on the shallow surface and the deep part is in the state of reverse bending force.The strain rate increases with the increase of time in each stage.In the middle of the slope,except for the arc transition part,which bears the pressure on the upper and lower sides,both sides are in the state of overturning force.?According to the crack growth pattern and the whole deformation and failure phenomenon,and tracing the direction of the new crack extension to describe the fracture surface,the whole deformation and failure area can be divided into the lower near "arc" main fracture section and the upper multi-stage secondary fracture section.(7)Based on the laws and phenomena revealed by physical model tests,the formation and evolution process and mechanical mechanism of anti-dip stratified slope with cracks are demonstrated and analyzed by using discrete element numerical experiments.Combining with the evolution and deformation characteristics and stress characteristics of the slope fracture surface,the whole evolution process characteristics of the anti-dip stratified slope fracture surface are analyzed,and compared with the large centrifugal test,14 kinds of crack propagation manifestations of 8 categories are summarized.According to its mechanical origin,five main deformation and failure modes of the formation and evolution of the fracture surface at various parts of the slope are classified,i.e.,the fracture surface of compression-tension type,the fracture surface of compression-shear type with gentle dip angle,the fracture surface of compression type,the fracture surface of tension type and the fracture surface of bending type.The deformation and failure characteristics of the collapse deformation evolution after the formation of the fracture surface are analyzed.Finally,it is proposed that the mode of deformation and failure of anti-dip layered slope controlled by steep and gentle fracture structure is "compressive shearing,reverse bending,shear breaking,toppling ". |
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