Research On Deformation And Failure Mechanism Of Fractured Rock Mass Under Uniaxial Compression

There are a large number of joint fractures in the rock mass,which is a kind of discontinuous and anisotropic complex medium.Such complex medium is very common in mining engineering,water conservancy engineering and underground construction engineering.The adjacent joint cracks in the fractured rock body will expand and penetrate under the disturbance of the engineering,which will reduce the overall strength of the rock mass and cause serious safety hazards to the underground works built in the rock mass.Therefore,the study of mechanical properties and deformation failure mechanism of fractured rock masses has important theoretical guidance significance for the actual geotechnical engineering construction.This paper combines the National Natural Science Foundation of China（Grant No.41672303）,based on the uniaxial compression test of pre-existing fissured rock material specimens,and combines numerical simulations.The geometric parameters of fractures under different uniaxial compression and fracture rock mass mechanics with different fracture distributions Characteristics,acoustic emission characteristics,and destruction mechanisms were studied.The main results of this paper are as follows:（1）The crack length,rock bridge length and crack opening degree have a great influence on the strength of the fracture test piece.The strength of the test piece is negative exponential function of the crack length.The decrease in the length of the rock bridge leads to a decrease in the strength of the test piece.The strength is much higher than that of open fracture specimens.The influence of the cross-crack cross angle on the strength of the specimen is controlled by the length of the rock bridge.When the rock bridge is 20mm,the variation of specimen strength with the angle of intersection is generally V-shaped;when the rock bridge is 0（fracture direct intersection）,the strength of the specimen increases with the increase of the angle of intersection.（2）The pre-peak stress-strain curve of the intact specimen is a straight line,which belongs to the obvious elastic deformation.The peak point is sharp,and the peak curve is sharply decreased;the single-fissure specimen has large plastic deformation before the peak stress,and the stress does not drop rapidly after the peak value.There is a certain stage of yielding platform.When the rock bridge is 20mm,the stress-strain curve of the parallel fracture specimen has a short yielding platform before the stress reaches the peak,and the stress after the peak falls more slowly;the stress-strain curve of the cross fracture specimen at the intersection angle between30⁰and 60⁰is the peak.The points are rounded,the pre-peak curve is consistent with the pre-peak curve of the complete specimen,and the stress after the peak falls more slowly;the stress-strain curve of the cross-crack specimen with the 90-intersection angle is multimodal,with a certain stage of yielding platform after the peak.The stress-strain curve of the directly intersecting cross-fissure specimen is consistent with the stress-strain curve of the single-fissure specimen.（3）Acousticemissioncharacteristicsofsingle-fissurespecimensand cross-fissure specimens are the same,which is shorter than the acoustic emission concentration area of the complete specimen.The acoustic emission of the open-type fracture specimen is more active from the beginning of loading.（4）The single fissure specimen is mainly caused by airfoil cracks generated at both ends of pre-fabricated cracks and parallel to the axial stress to damage the upper and lower ends of the specimen.The crack angle of the airfoil crack and the minimum J₂ theoretical calculation are obtained.Split angle is basically the same.The intersection angle has a great influence on the failure mechanism of the cross fracture specimen with 20mm rock bridge.When the angle of intersection is small,the airfoil cracks generated at the upper and lower ends of the primary and secondary fractures will cut through the rock bridge and extend through the entire test piece.When the intersecting angle is 60⁰,the secondary fracture is not involved in the destruction of the specimen,and the destruction of the specimen is controlled by the primary fracture.When the angle of intersection is large,the main crack and the airfoil cracks generated at the lower end of the secondary fracture do not merge.The parallel and axial stresses develop toward the ends of the test piece,and the test piece is broken through multiple through faces.When the intersection angle of the rock bridge is0mm,when the angle of intersection is small,the primary fracture and secondary fracture will form a combined fracture that controls the destruction of the test piece.The combined fracture and the airfoil cracks generated at both ends form the failure surface of the penetration test piece.The test piece is damaged;when the intersection angle is large,airfoil cracks will occur at the lower ends of the primary and secondary fractures,and they will develop independently to the lower end of the test piece,resulting in more energy consumption.Crack opening has little effect on the damage mechanism of the specimen.The stress concentration at the pre-formed crack tip causes the generation and propagation of secondary cracks,and it also continuously guides the extension of the fracture.