Research On The Characteristics Of Rock Three-Dimensional Crack Fracture Propagation Under Seepage And Stress Coupling

Crack widely exists in natural rock mass, most buckling failure rock mass are radically caused by crack propagatin and damage evolution, so the research on three-dimensional crack is always an important topic in geotechnical field. The method of theoretical research, combination of numerical calculation and laboratory test are used to systematically studies three-dimensional crack damage propagation characters and mechanisms of real rock mass under hydromechanical coupling.The bedrock which contained pore network is regarded as the pore-fissure media base on the double-porosity theory, and combines percolation theory, a pore-fracture hydraulic exchange characteristic equation of bedrock system and fissure system is established; base on rock damage theory, the cracks' progagation under seepage pressure are studied,then crack critical osmotic pressure formula under hydromechanical coupling is deduced. The wing crack and initial fissure can be simplisfed as a plance crack with the diameter of 2L, and the formula for calculating the stress strength factor of the wing crack tip is calculated.The matrix scaffold and pore water are assumed to bear the total stress produced by loads together, and the initial equivalent damage flexibility tensor of crack rock is established according to superpose the elastic flexibility tensor and additional flexibility tensor caused by defect.According to the fracture mechanics and damage mechanics. The fracture mechanics are used to analyze the characteristics of wing crack initiation and propagation under hydromechanical coupling, then the additional flexibility tensor is established in the consideration of crack initial damage,damage evolution, wing crack propagation and other kinds of damage mechanisms, and constitutive model equation of three-dimensional crack propagation damage under hydromechanical coupling is derived.According to Lemaitre strain equivalence hypothesis, the composite damage tensor of micro and macro-defect coupled is derived in consideration of macro defect and micro defect of crack.The finite difference soft ware FLAC3D is used as the platform to do secondary development, and the sample model which contained three-dimensional surface single crack is established to simulates the propagation of three-dimensional crack damage, and the seepage test of real rock sample with single crack has been taken to prove the veracity of the model. It can be seen that three-dimensional crack start with wing crack and against-wing-crack follows closely. Compared to intact rock, the weaken amplitude with different steep fracture crack strength range from 18.7% to 25.3%, and increase with prefabricated cracks angle, peak value reduce from 9.9% to 13.8%, and post-peak strength reduce from 8.6% to 13.9%. Besides, Fracture extension stress nephogram shows that the centralized region of tension-shear stress is main crack place of wing crack,while the against-wing-crack is caused by compression-shear stress; except wing cracks and against-wing cracks, cut cracks with the cross of preset crack have been found. The damage mode of crack sample are not same with different angle, it mainly concludes cut damage with 30° crack angle,X mode damage with 45° crack angle and reverse-Y mode damage with 60°crack angle, however, the damage of samples are end with wing crack coalescence or with against-wing-crack.