| The western ecological environment is fragile and water resources are scarce.Engineering disturbance in underground engineering will cause irreversible damage to aquifer strata.After the engineering disturbance,the stability of boundary cracks in water-resisting strata is very important to keep water resources from losing.In this thesis,the criterion of rock boundary crack propagation under compression-shear state is given based on the previous studies,considering the change of water on rock occurrence conditions in water environment.At the same time,this criterion combines expansion,deterioration and other factors.Also,the criterion is verified by physical experiments.The main work of this thesis includes:Based on the D-P failure criterion of rock and the stress field expansion expression at the crack tip,the expression for calculating the fracture toughness of rock is derived.Rock samples in dry?natural state?water content of 2.3%?water content of 2.5% and natural saturation state were prepared and fracture toughness test and rock shear test were carried out.Through shear test and maximum circumferential stress criterion,the selection methods of parameters in calculating rock fracture toughness are determined,which can provide reference for engineering application.The mode I-II fracture toughness of rocks with different water-bearing conditions was tested by STCA method,and the calculated results were verified.According to the actual situation,the cracks can be divided into mode of open and closed.Based on the complex function method and considering the factors of crack tip expansion,the expressions for calculating the stress intensity factors of cracks in waterbearing rock boundary under two kinds of crack states are derived.At the same time,combining with the empirical expression of compression-shear crack fracture,the crack initiation criterion of water-bearing boundary crack is obtained.Compression-shear tests were carried out on specimens with boundary cracks in different water-bearing states,and the calculated results of the criterion for initiation of boundary cracks in compression-shear were verified.Also,the influence of horizontal lateral pressure on boundary crack growth is analyzed by using self-made lateral pressure loading device,and the accuracy of crack initiation criterion is further verified.Based on the parametric analysis of the factors influencing the stress intensity factors of rock water-bearing boundary cracks,such as crack geometric parameters and water-bearing conditions,the influence laws of the parameters on the stress intensity factors of cracks are obtained.The variation of compression-shear coefficient with crack geometric parameters is analyzed. |
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