Study On Failure Mode And Strength Characteristics Of Prefabricated Double Crack Joint Specimens

The rock slope contains a large number of irregular rock joints,and its development structure and failure mechanism have a very important impact on the stability of the slope.In order to solve the instability problem caused by the failure of the joint surface of the rock slope,this paper takes the Xinqiao mining area in Tongling City as the background,adopts the research method of combining theoretical analysis,experimental analysis and numerical simulation,analyzes the stability of the rock slope under the parallel double joint fracture surface with different factors,and determines the optimal support mode based on the actual situation.（1）The basic parameters of the slope are obtained through the field survey,and the physical and mechanical tests are carried out on the rocks of different rock layers,and the basic mechanical parameters of the rocks are obtained.The pre fabricated double joint specimens were prepared.The influence of the crack angle,length and width on the shear strength of rock specimens containing pre fabricated cracks under biaxial shear was analyzed by using the orthogonal design method.The influence level of each factor was determined as vertical stress>crack spacing>crack length>crack thickness>crack angle.The optimal scheme was A₄B₂C₅D₁E₂,that is,when the crack spacing was 5 mm,the crack thickness was 0.5 mm,When the vertical stress is 60 KN,the crack length is 10 mm,and the crack angle is 30°,the shear strength and stability of the specimen are the highest.（2）Based on the analysis of the cracks in pre cracked rock specimens,the cracks can be divided into four types according to their development modes:the single main shear crack through mode;Main shear crack coalescence and secondary tensile shear crack propagation mode;Main shear crack coalescence and secondary shear crack propagation modes;Main shear crack coalescence and secondary tensile crack propagation mode.Through the rock like biaxial shear test,it is concluded that when the distance between parallel double joints is fixed,with the increase of joint length and thickness,the breakthrough mode gradually changes from the initial shear failure to the failure mode under the combined action of tension and shear.（3）Combined with the actual construction conditions and experimental results in the mining area,a section map of Xinqiao Mine is selected.The Rhino modeling software is used to establish a basic slope model to simulate the slope excavation process.The FLAC3D software is used to calculate the stability of the slope.It is obtained that the slope and displacement increase with the increase of the number of excavation layers.The maximum vertical displacement is 5.75 cm,the maximum horizontal displacement is 4.45 cm,and the displacement basically occurs at the foot of the newly excavated slope;The safety factor of the slope decreases with the increase of the number of excavation layers.When the excavation reaches the fifth layer,the safety factor is 1.152,which is lower than the allowable safety factor of the mine slope engineering.Manual support is required to ensure the sufficient stability of the slope.（4）The slope is supported by prestressed anchor cable.The numerical simulation results under different support modes are compared by FLAC3D software,and the influence of different anchor diameters,anchor spacing,and anchor angles on the slope stability is analyzed.After comparison,the final support scheme for the slope is selected as follows:prestressed 800 KN,anchor cable length 20 m,anchor cable diameter 40 mm,anchor cable spacing 4 m,and anchor angle 45°,the results provide a theoretical reference value for the project site.Figure 51 Table 20 Reference 81...