Numerical Simulation Of Rock Crack Propagation In Closed Contact Mode

Natural rock masses contain different types of discontinuous structures.Such as cracks,joints,bedding,faults and shear zones.These discontinuous structural surfaces are inclined to cracking,propagating,penetrating and slipping under the external loads,which significantly affect the physical and mechanical properties of the rock mass.In rock mass engineering,the failure of rock mass is closely related to the development,propagation and penetration of cracks.Therefore,studying the mechanism and characteristics of crack propagation has important engineering significance for rock engineering including fractured rock slopes,deep-buried roadways and tunnels.First,using traditional fracture mechanics theory and fracture simulation method based on localized strength theory,the crack propagation process of Brazilian discs with different types of initial cracks is studied.When the propagation step is too large,the traditional fracture criterion is used to calculate zigzag cracks,especially closed cracks.The results show that the positive and negative changes of the type II intensity factor K_II are affected,due to the initial contact between the cracks.It results in the crack propagation path showing a zigzag pattern,which does not match the actual results.And the fracture simulation method based on the localized strength theory proposes that the cracks are basically not affected by the expansion step length and are smooth curves,which solves the problem of zigzag cracks in the calculation of the traditional fracture criterion.The fracture simulation method can not only judge and calculate the extension of tensile cracks and shear cracks at the same time,but also combines the crack growth increment method to simplify the calculation method and improve the calculation efficiency.In order to study the crack initiation and propagation process of closed-contact fractured rock,the model adopts the Brazilian disc with the initial closed fracture to compare the crack propagation law under the compressive shear stress state,focusing on the initial fracture inclination?,disc and the friction coefficient of Brazilian disc?₁ and the friction coefficient between closed cracks?₂ and the loading method on crack propagation.Under the condition of progressive displacement loading,all tensile cracks are obtained and they are unstable failures,and the influence of different friction coefficients on crack initiation and propagation angle,propagation path and contact state is analyzed.If a large displacement load is applied instantaneously,at the same time Both tensile and shear cracks are produced,and the increase of?₂ will inhibit the initiation and propagation of shear cracks.In the Brazilian disc test with initial cracks,broken areas are often produced around the contact points,which together with the crack penetration at the cracks lead to the destruction of the disc.The use of flat Brazilian discs can solve the problem of"stress concentration"well.Aiming at the crack propagation law of flat Brazilian discs with oblique central cracks,the effects of initial crack inclination?and friction coefficients?₁ and?₂ on crack propagation are studied.Similar to the complete Brazilian disc,tensile cracks are obtained by calculation,and the influence of different friction coefficients on crack propagation angle,propagation path and contact state is analyzed.Using the fracture simulation method of localized strength theory,a study on the failure of the locking section of the"three-section"slopes is carried out,and the influence of the friction coefficient?₂ of the creeping section of the leading edge on the locking section is explored.The results show that the increase of?₂ restrains the slip of the sliding body in the rock slope,and restrains the rock slope with locking section from occurring as a whole.Related researches provide research ideas for the prevention and control of"three-stage"slopes,and further illustrate the advancement and applicability of the fracture simulation method.