| Circular roadway is widely used in deep underground engineering.Work such as Chambers,roads and tunnels can often be reduced to mechanical analysis of rock structures with holes,and the excavation of these rock masses inevitably causes damage and destruction to the surrounding rock,resulting in fractures around the holes.Due to the difficulty of sampling the original rock,the study of pore and fractured rock mass mainly relies on laboratory tests.Based around fracture of 45 ° and the Angle between the horizontal plane for class rock materials(cement,fine sand,and water with a mass ratio of 26:25:10 as cement mortar)as an example,using the theory of rock mechanics and fracture mechanics,combined with high-definition industrial cameras and high-precision strain gauges,the biaxial compression test process and results of prefabricated rock-like materials around pores were analyzed.The crack initiation and fracture principle before and after reinforcement of prefabricated cracks around a hole and a single hole rock-like materials were studied;the effects of lateral pressure and different reinforcement thicknesses on the crack penetration rules around pores in rock-like materials were explored;Local strain characteristics of fractured rock samples with holes and prefabricated cracks around the holes were analyzed.The research shows that:(1)Reinforcement of aluminum pipe under the same side has a more obvious positive impact on the peak strength of the specimen,and the thicker the thickness,the greater the impact,the strength increase range of reinforced specimens compared with unreinforced specimens is 6.05% ? 42.22%.In addition,the peak strength of the specimens with the same aluminum tube reinforcement thickness and different side pressures will increase as the side pressure increases.The strength of the specimen with a lateral pressure greater than 0 MPa is improved by 2.36% ? 66.52% compared to the specimen with a lateral pressure of 0 MPa.(2)The failure modes of specimens with holes can be divided into five types,namely single-slope type-I,single-slope type-II,single-slope type-III,inclined T-type and single-site shear type.These five types of failure modes are shear cracks that expand into fracture surfaces,and far-field cracks and initial tensile cracks do not cause fracture surfaces.The failure modes of the specimens containing holes and prefabricated cracks around the holes can be divided into 4 types,which are single-slope type,"herringbone" type,inclined T-type and "?" type,among which there are far-field cracks and initial tensile Extension cracks form fracture surfaces.(3)For the specimens with holes,taking the specimens without reinforcement with holes SN0-1,0-2,0-3,0-4 as an example,only when the lateral pressure is 0 MPa,the far field cracks appear obvious.The failure modes of the specimens are basically the same,that is the left and right shear cracks of the hole extend into a slope;while the influence of lateral pressure and reinforcement thickness of prefabricated cracks around a hole and a single hole rock-like materials on crack propagation is not very obvious.The initial cracks and failure modes of specimens with the same reinforcement thickness or the same lateral pressure are basically the same;(4)For rock-like specimens containing pores and fissures around the pores.The local strains measured by the strain gauges of all the specimens did not show a peak at the peak strength of the specimens.No obvious strain concentration phenomenon was found during the entire loading process of the specimens.The state of strain concentration is weak(strain concentration factor is less than 1).(5)The number of local strain jumps for rock samples with holes is almost the same(all three times).There is no regular pattern for the cracking time of the specimen.Under the same failure mode of strain jump time,the initial local strain jump time of the specimen is close. |
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