| Most of the natural structural planes in engineering rock masses exist in the form of filling joints.Under external loading,the rock masses are likely to undergo shear failure along the filling joint,which brings great safety risks to the stability of rock mass.Therefore,it is of great practical engineering significance to study the shear failure characteristics of filling joints and the anchoring effect of bolt for the strength evaluation and stability control of rock mass.In this paper,the filling joint is taken as the research object,and the shear test program is designed considering different influencing factors.The mechanical effects of the thickness of the filler and structural surface morphology on its shear strength and deformation are explored.The bolts are used to strengthen the filling joints,and the mechanical response of filling joints under anchoring is studied.In the Particle Flow Code program,Fish language is used to realize the real-time monitoring of the microscopic indicators of filling joint and anchorage system in the shearing process,and the time-effect display of the microscopic evolution is realized,so as to achieve the comparison with the physical shear test.1.Considering the two factors of structural surface morphology and filling thickness,the shear mechanical effects of filling joints are analyzed,and the calculation method of filling degree of three-dimensional anisotropic structural surface and standard JRC surface is studied.The stress of anchor bolt in the anchoring system is analyzed,and the strengthening mechanism of anchor bolt on joint shear strength is emphatically studied,which provides theoretical guidance for the analysis of filling joint anchorage system.2.The indoor shear test was performed on the filling joint.Based on the test results,the influence of different structural surface and different filling thicknesses on the shear of filling joint was analyzed and summarized.The results show that the peak shear stress of the filling joint increases with the increase of JRC value,but decreases nonlinearly with the filling thickness;The shear of filling joint is affected by the combination of the structure surface and the filling thickness,When there is no filling or filling thickness is less than the undulation of the structural surface,the peak shear stress is more sensitive to the change of the morphology of the structural surface,and when the filling thickness is greater than the undulation of the structural surface,the morphology of the structural surface is no longer the main influencing factor;for the joint with a smaller JRC,only the small filling thickness affects the apparent change of its shear strength,as the filling thickness increases,the shear strength tends to a relatively stable value,the larger the joint JRC,the more obvious the effect of the change in filling thickness on its shear strength.3.Based on the comparative analysis of the curves between unfilled and filled joints,it is found that the peak shear failure of unfilled joint tends to be instantaneous failure,the strain softening is obvious,while the peak shear of filled joint appears as a stage,which is related to the interaction between filling material and structural surface,and the degree of strain softening is obviously reduced;there are two forms of filling joint shear curves:single peak type and double peak type,among which the double peak type generally occurs in joints with large fluctuations.4.Based on the results of filling and anchoring joint shear test,the anchoring effect of bolt on structural surface with different filling thicknesses and different JRC values was analyzed.The results show that the shear strength of filling joints increases to a certain extent after the application of the bolt;As the filling thickness increases,the peak anchorage strength of filling joint decreases,and the contribution value of bolt to the shear strength of filling joint increase first and then decrease;When the filling thickness is less than the fluctuation of joint,the bolt acts as a "pin",the shear displacement of the structural surface significantly increases when the shear stress reaches the peak,When the filling thickness is greater than the undulation of the joint,the shear resistance stage of the bolt reduced obviously,the shear resistance performance cannot be fully exerted;as the JRC value increases,the contribution value of bolt to the peak strength of filling joint also increases slightly,but the larger the JRC,the greater the degree of shear fracture of the sample,cause the lower residual strength.5.Using PFC to simulate the shearing process of filling joints,analyze the law of displacement vector,the contact force and the crack evolution in the shear process,and compare the differences in microscopic fracture failure under different filling thicknesses.It is found that the change of displacement vector of filling joint was obviously affected by the filling material in the early stage of shearing,showing a symmetrical displacement of the arc centered on the filling material,while in the later stage of shearing,the upper and lower specimens showed independent displacement characteristics.Under the influence of shear stress and normal stress,the redistribution of contact force between grains occurred during the filling joint shearing process,and it was mainly biased towards the force boundary,and gradually towards the structure,the contact force concentration phenomenon appeared at the large protrusions of the structural surface;the shear cracks are first generated at both ends of the filling,and then gradually developed along the filling joint towards the rock interior.As the filling thickness increases,the initial crack growth rate increased,but the total number of cracks decreased.The microscopic failure of the sample is mainly caused by the backfill,and the failure degree of jointed rock mass is reduced with the increase of filling thickness,finally,the specimen forms a macroscopic shear fracture zone along the filling joint and thereby failed.6.Based on the numerical simulation results of anchoring and filling joints,the shear characteristics of anchorage system are analyzed from a microscopic perspective.It is found that the concentration of contact force mainly occurs at the bulge of the joint and around the bolt,the initial shear contact force is center-symmetrical,As the shear displacement increases,the concentrated distribution area of contact force decreases,and gradually develop towards the intersection of the bolt and the filling joint.From the microscopic failure process,it can be seen that the main failure area of the anchorage system under the external shear load occurs on the structural surface and along the length of the bolt,with the development of these areas,the failure of the filling joint and the fracture of local jointed rock mass are finally shown,the maximum deformation area of the bolt occurs at the filling structure surface,with the thickness increases,the particle damage around the bolt is relatively reduced,and the fragmentation degree of rock mass is reduced. |
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