Uniaxial Compression Test And Numerical Simulation Of Like-rock Materials With Pre-crack

Using cement mortar material to prepare rock like material specimen with gradual defect from crack to round hole.Through uniaxial compression test on the prefabricated rock-like defects,the change values of the size of the prepared rock-like defects m(m=(a-b)/(a+b))is 0,0.14,0.33,0.60 and 0.95,and the included angles ? with normal stress are 0 °,15 ° 30 °,45 °,60 °,75 ° and 90 °,combined with the theory of rock fracture mechanics,laboratory test and numerical simulation,the mechanical response mechanism of the defective rock under uniaxial compression is obtained.The influence of such variables as the defect angle on the failure characteristics of the defective rock specimen is analyzed.It is of great significance to increase the understanding of the underground builders and workers on the expansion characteristics of the rock with specific defects,and to predict the failure of the rock structure around the underground engineering The main conclusions of this paper are as follows:(1)The existence of defects weakens the peak strength of this test,among which the circular hole defect weakens the strength most obviously;the peak strength of the specimen with defects increases with the increase of m value,and the peak strength of the specimen with defects is the largest when the dip angle of defects is ? = 0 ° and when the long axis of defects is parallel to the stress loaded;the peak strength of the specimen with defects increases with the dip angle of defects The peak strength of the defect specimen is the lowest when the dip angle reaches 45 °and 60 °;(2)The crack initiation point of the defective specimen is affected by the defect m value and the inclination angle ?.When the value of M is fixed,? increases from 0 ° to 90 °,the crack initiation point gradually moves from the end of the long axis to the end of the short axis;when ? is fixed,with the decrease of m value,the crack initiation point shifts from near the end of the long axis to near the end of the short axis.Through numerical simulation and theoretical analysis,it can be seen that the main reason is that when m decreases,the area of tensile stress concentration in the defect specimen decreases,which leads to the decrease of the area of tensile stress concentration in the crack initiation,so that the crack initiation point shifts to the vicinity of the short axis;(3)The crack growth of the defective specimen is that the tensile crack is initiated at the upper and lower points of the defect and propagates along the direction of the main stress.With the increase of the load,the tensile crack of some specimens disappears to the naked eye parts,while the shear crack is initiated at the left and right ends of the defect and propagates along the diagonal to form the final failure surface.When the m value is small,some specimens will also propagate along the initial tension The crack breaks and the surface peels off at the left and right ends of the defect.Through the numerical simulation analysis,the crack initiation at the upper and lower ends is mainly due to the tensile stress concentration at the upper and lower parts of the defect,while the shear crack at the left and right ends is mainly due to the compression stress concentration;(4)The statistical analysis of the number of shear cracks,tensile cracks and total cracks in the process of crack development shows that the closer the crack development is to the peak value,the greater the rate of increase is,and the maximum rate of increase is after reaching the peak value.The crack growth accelerates with the initiation of internal cracks in the process of load failure;(5)The penetration failure surface of the defect specimen can be divided into two parts: tensile failure without debris and friction trace on the penetration surface and shear failure surface with obvious scratch and debris.According to the penetrating failure surface,the ultimate failure mode of the defective specimen can be divided into the shear failure mode of only the shear failure surface and the tension shear mixed failure mode of both the shear failure surface and the tension failure surface.The initial crack does not necessarily develop into the final failure surface.