Research On Meso-mechanism Of Failure Mode Of Tunnel In Jointed And Cracked Rock Mass

The problem of crack propagation and penetration in fractured rock mass is an important research topic in the field of geotechnical engineering,and has important theoretical guiding significance for engineering design,construction,monitoring,maintenance and so on.In order to explore the influence of the existence of cracks on the failure characteristics of cracked rock mass,theoretical analysis,laboratory tests and numerical simulation methods were comprehensively used in this paper to study prefabricated cracked rock materials.The main research results are as follows:（1）Rock-like materials were used for the prefabricated primary and secondary cracks laboratory tests,and five sets of tests were conducted for different combinations of primary and secondary cracks.The results showed that:In the case of different crack combinations,the tip of the main crack starts first;When the primary and secondary cracks intersect,only the right tip of the secondary crack begins to crack,and the crack initiation time is later.When the primary and secondary cracks are separated,the crack initiation occurs almost at the same time;The larger the distance between the primary and secondary cracks,the smaller the peak strength and the lower the probability of penetration.（2）PFC^2Dwas used to establish the uniaxial compression test model,and the influence analysis of the meso-parameters of particles and contact was carried out.The results showed that:The particle friction coefficient is positively correlated with the Elastic modulus and Peak strength,and the bond stiffness ratio is positively correlated with the Peak strength and negatively correlated with the Elastic modulus;The bond tensile strength and bond cohesion mainly affect the Peak strength,and both are positively correlated with it;The bond modulus mainly affects the Elastic modulus,and they show a positive correlation.（3）PFC^2Dwas used to simulate the uniaxial compression of specimens with single prefabricated closed crack.Most of the Elastic modulus,Secant modulus,Deformation modulus,Peak strength and Peak strain of the specimen showed a downward trend with the increase of crack length and inclination angle;The secondary cracks appear later than the wing cracks,and micro cracks mainly emerge around the prefabricated cracks,and when the length of the prefabricated cracks was small,the micro cracks in the areas other than the prefabricated cracks were more likely to appear;With the increase of crack length and inclination angle,the stress at the moment when the first micro crack appears decreased first and then increased;The growth curve of micro cracks can be divided into three stages:unappearing,unstable growth and rapid growth.（4）PFC^2Dwas used to simulate uniaxial compression of specimens with double prefabricated closed cracks.Change the length of the rock bridge while keeping the inclination angle unchanged,when the length of the rock bridge is 13mm,the double prefabricated cracks have two penetrations,and the other working conditions have one penetration;As the length of the rock bridge increased,the peak stress increases first and then decreases,and the stress when the first micro crack appearing changes not large.Change the inclination angle of the rock bridge while keeping the length unchanged,when the inclination of the rock bridge is-15°and-75°,there are three penetrations of the double crack,four penetrations at-45°,and one penetration at 15°,45°and 75°.As the inclination angle of the rock bridge increases,the peak stress increases first,then decreases and then increases,and the stress at the moment when the first micro crack appears first decreases then increases.（5）PFC^2Dwas used to simulate the tunnel with closed cracks.The larger the prefabricated crack inclination angle on the upper side of the tunnel,the distance from the tunnel and the length of the crack,the closer the final failure mode of the specimen is to the crack-free specimen;For prefabricated crack with a certain length,the initiation of the end of the crack is mainly affected by its inclination,the larger the inclination of the crack,the earlier the crack initiation;The closer the prefabricated crack is to the tunnel,the easier it is to penetrate.