Experimental Study On Mechanical Properties Of Rock Masses With Internal Fracture Defects

Due to the existence of different forms and different types of fracture defects in the rock,it causes the discontinuity and anisotropy of the rock,which affects the mechanical properties such as the strength and deformation of the rock.Deformation characteristics are the basis of engineering stability evaluation.However,whether it is excavation,unloading,or fractured rock mass produced by geological movements,the widths of the fractures are different,and the forms of occurrence are different,which causes the strength and deformation characteristics to vary.In addition,most scholars have simplified the fractured rock masses into two-dimensional models,and the study of invisible rock fractures is not comprehensive enough.Therefore,two different types of internal fractures are designed to open and close.By changing the size,inclination,number,and shape of fractures,the strength and deformation characteristics of flawed rock masses with internal fractures under uni-axial compression are recognized and understood.The technical methods of launch acquisition and digital photography further analyze the internal crack evolution and penetrating failure modes.Finally,a combination of laboratory tests and numerical simulations is used to comprehensively understand the mechanical characteristics of flawed rock masses with internal fractures under uniaxial compression.The main research results obtained are as follows:(1)The uniaxial compression test is used to analyze the deformation and mechanical characteristics of the internal cracks.The research shows that the test specimens with the cracks become larger with the crack size,and the peak stress is from the theoretically minimum 45°fracture angle to 30°offset,double-fracture specimens are offset to 15°.The changes in peak strain,elastic modulus,and secant modulus are complex.The through failure mode is mainly tensile failure,and the 60° and 75° test blocks are mainly shear failure.(2)By analyzing the closed fracture deformation and mechanical characteristics of three different inclination angles and multiple fracture forms at 30°,45°,and 60°,it is shown that the change of the rock bridge has the smallest effect on the peak stress change of the test block,and the remaining three forms of fractures The impact on the test block is more complicated,and specific problems need to be analyzed.The test block with an inclination of 30°is tensile failure,and the test blocks with 45°and 60°are tensile and shear failures.(3)Acoustic emission acquisition results show that when the crack size is large,the accumulated AE count is lower.Due to the larger internal defects of the test block,the ringing count generated by internal crack development is relatively small.(4)Based on the results of laboratory tests,a particle flow model of internal fracturedefective rock masses with different fracture forms was established,and a comparative study of circular fractures at three different angles was carried out.The research results show that: in the initial compaction stage,cracks first occur around the internal cracks,and then cracks occur between the sphere and the wall.The two cracks continue to develop and evolve,and eventually form a through failure.