Research On Creep Fractured Test And Numerical Simulation Of Discontinuous Fractured Rock Masses

With the rapid development of national economy,a variety of large-scale engineering projects are springing up.As a relatively common structure in engineering,complex mechanical properties of discontinuous fractured rock mass,especially rheology,greatly increase the difficulty of the project.Based on the project of National Natural Science Foundation of China:anisotropic rheological characteristics of rock mass with intermittent joints and microscopic time-dependent rupture mechanism,a series of tests related to discontinuous fractured rock mass have been carried out,including uniaxial compression test of double-preset fractured specimen and uniaxial compression orthogonal test for multi-preset fractured specimen,uniaxial compression controlled test for multi-preset fissured specimen and uniaxial creep test for multi-preset fissured specimen.The effects of different distribution forms of fractures on the instantaneous and long-term mechanical properties of the specimens are analyzed,and verified by numerical simulation of PFC.The main results are as follows:1.Based on two special geometric distributions of parallel staggered and collinear double fractures,uniaxial compression tests are carried out to study the influence of different fracture distribution on the mechanical properties of the specimens.It is found that when the prefabricated fractures are parallel interlaced,with the increase of the dislocation distance,the strength and modulus of the specimens increase as a whole.When the prefabricated fractures is collinear,the peak strength and elastic modulus of the specimens decrease continuously with the increase of the inclination angle of the preset fractures,and the smaller the angle between the inclination angle of the preset fractures and the uniaxial pressure direction,the more prone to shear through failure.2.Based on four different fracture distribution forms,such as inclination angle of preset fractures,length of rock bridges,length of fissures and spacing of fissures,uniaxial compression orthogonal test is carried out for multi-preset fractured specimens.The sensitivity of different fracture distribution factors to the mechanical properties of specimens were studied,and the uniaxial compression control test of multi-preset fractured samples was carried out to study the influence of the different levels of the same factor on the mechanical properties of the specimens.We found that the influence of inclination angle of preset fractures on the strength of multi-fracture test is the biggest,the crack length is the second,then the length of rock bridges,and the influence of crack spacing is the least.The influence of inclination angle of prefabricated crack on the elastic modulus of multi-fissure specimens is the greatest,followed by the length of the cracks,then the spacing between the cracks,and the influence of the rock bridges length is the least.Increase of the inclination angle of the cracks,strength and elastic modulus of pre-existing fractured specimens increases.With the increase of the length of rock bridges,compressive strength and elastic modulus the specimens also increases.Increasing of the length of the cracks,compressive strength and elastic modulus of the specimens reduce.Increasing of the spacing between fractures,the compressive strength and elastic modulus of the samples increases,and the increase in compressive strength is becoming smaller.3.Based on the uniaxial compression test of multi-preset fractured specimens,the uniaxial compression creep test of multi-preset fractured specimen is carried out,and the influence of different fracture distribution on the creep characteristics of specimens is analyzed.With the increase of creep-driven stress ratio,The creep quantities at all levels of specimens are exponentially increasing in the form of y=y₀+A₀e^R0x?x is the creep stress-driven ratio?,and the ratio of creep quantity to instantaneous strain is also exponentially increasing in the form of y=y₀+A₀e^R0x?x is the creep stress driven ratio?.When the creep driving stress is the same,the creep growth rate increases gradually with the increase of the inclination of prefabricated fractures,but the decay rate of the creep growth rate decreases gradually,and the ratio of creep quantity to instantaneous strain increases gradually.The closer the dip angle of fracture is to the diagonal inclination angle of specimens,the more prone is shear failure to the specimens,otherwise it is more likely to occur tensile failure.With the increase of the bridge length of the prefabricated fractured rock,the decay rate of creep growth rate decreases gradually,and the failure mode of the specimen gradually changes from tensile failure to shear mode.With the increase of the length of the preset fractures,the creep quantity of all levels of the specimen increases,the ratio of the creep quantity of the instantaneous specimen to the instantaneous strain increases,and the number of cracks produced during the failure of the specimen decreases obviously,and the main through cracks are getting shorter and shorter.With the increase of the distance between the prefabricated fractures,the creep quantity of the specimens decreases and the ratio of the creep quantity to the instantaneous strain decreases continuously.,and the failure mode of specimens are obviously transitioned from vertical through failure to transverse through failure.