Study On The Mechanism Of Closed Crack Propagation In Rocks

Joints or fissures in natural rock masses are mostly in closed state.The study on the crack initiation and propagation influenced by different friction coefficients plays a significant role in many fields such as slopes instability,deep mining and deep burial of radioactive material.In this paper,fracture mechanism theory and strength theory are used?A series of numerical simulations are carried out through using APDL to consider effect of frictional contact on the crack initiation,propagation and coalescence of the closed crack subjected to compression,and the following conclusions are drawn:(1)When the flat plate with closed oblique crack is subjected to uniaxial compression,the propagation trajectory of tensile cracks becomes less curved with the increase of the friction coefficient of the crack surface.(2)When the flat plate with closed oblique crack is subjected to a high-level uniaxial compression,the shear cracks begin to initiate and propagate in unstable manner.The friction coefficient is larger,the more difficult for tensile cracks initiate and propagate with the same angled crack subjected to compression.When the friction coefficient reaches a certain value,the initiation of tensile cracks vanishes.At this time,with the increase of compression load,the shear crack propagation is completely present in the sample.(3)The tensile cracks may get closed and their propagation may terminate during the propagation of shear cracks with the increase of the friction coefficient of the crack surface.Finally,the propagation of shear cracks dominates the failure of sample.(4)The coalescences of parallel crack are different from inclined angles of rock bridge.The smaller the inclined angle of the rock bridge,the coalescences are caused by the shear crack propagation.When the inclined angle increases,the coalescences are caused by both the shear crack and the tensile crack.When the rock bridge angle continues to increase to a certain,coalescences of the crack is caused only by the tensile cracks.(5)Under the biaxial compression,the smaller the inclination angle of the closed crack,the tensile cracks are affected more by the confining pressure,and the propagation length of the tensile cracks become shorter.With the friction coefficient increases,the propagation of the tensile crack terminates,especially when the shear cracks initiate,and the failure of sample is dominated by the propagation of the shear cracks.When the friction coefficient increases to a certain value,the shear cracks initiate first instead of the tensile cracks.