| The geological environment associated with the surrounding rock is increasingly complex under jointed action with high situ stress and water pressure due to rapid advancement of a large number of underground engineering constructions of transportation,water conservancy and hydropower,mining,etc.,and the increasing buried depth of underground structures.Under the coupling action of situ stress and water pressure,the flaws such as natural cracks,joints and faults in the rock mass will continue to propagate and coalesce through each other,causing deformation and damage of the rock mass and even instability and collapse,which finally lead to the occurrence of engineering accidents and disasters.The research on the deformation and failure mechanism of fractured rock mass under hydraulic coupling is of great significance for underground engineering design and disaster prevention and control,so it has received extensive attention in the academic community.Previous studies on rock mass failure focused on the fracture modes and mechanical behaviors of rock masses with penetrating flaw have obtained a large number of achievements,but these studies are distinguished with actual situation without the information of the three-dimensional shape and distribution of natural fractures.In addition,most of the previous studies on the three-dimensional fractured rock mass only considered the situ stress action rather than hydraulic coupling.In this paper,the fracture mechanics behavior of rock-like materials containing three-dimensional flaws under hydraulic coupling is investigated.Based on cement mortar-like rock materials to simulate real rock mass,lab experiments,discrete element simulation and acoustic emission techniques are used to investigate the crack propagation,coalescence modes of the 3D fissures and the final failure modes of specimens under hydraulic coupling conditions.The influence of the geometric distribution of the flaw and the loading condition on the crack propagation and coalescence are analyzed,and the spatial evolution law of the fractured rock mass is elucidated.The main developments and completions are as follows:1.The fracture mechanism of rock specimens containing three-dimensional single crack under hydraulic coupling was studied.Firstly,the propagation characteristics of the pre-crack and the ultimate failure modes of the specimens under different water pressures were investigated,and the similarities and differences between the failure modes of the specimens under the no-water condition and the hydraulic coupling condition were compared,so as to analyze the promoting effect of water pressure on the crack propagation of the wing.The changing mechanism of failure mode of specimens with different crack dip angle is summarized,and the influence of water pressure and crack dip angle on specimen fracture is analyzed.Then,on this basis,the variation trend of peak strength and characteristic stress with water pressure and crack dip angle was studied,and the failure mode and fracture mechanism of the specimen were analyzed.2.The interaction between three-dimensional cracks and the fractured mechanical behavior of specimen under hydraulic coupling were studied.The linking condition and the ultimate failure mode of pre-cracks within the specimen containing coplanar double cracks and parallel double cracks under 3MPa water pressure were investigated respectively,and the variation rules of the failure mode of the specimen under different conditions were summarized.The influence of the crack dip angle and the leading edge spacing of the coplanar crack on the failure mode of the specimen was studied and analyzed.The influence of crack spacing and rock bridge angle on the failure mode of specimens with parallel double fractures was studied and analyzed.Then,the effects of different controlling parameters on the peak strength and characteristic stress of the specimen were studied3.The jointed propagation of cracks and fractured mechanical behavior of specimens under hydraulic coupling were studied.In this paper,the linking condition and the final failure modes of the pre-crack specimens with coplanar double cracks and non-coplanar triple cracks specimens under 3MPa water pressure were investigated respectively,and the changing rules of the failure mode of the specimens were summarized.The influence of rock bridge angle ?1 on the linking mode of the specimen with coplanar double cracks was studied and analyzed.The influence of rock bridge angle ?2 on the linking mode of specimens with three non-parallel cracks was studied and analyzed.Then,the variation trend of mechanical properties of specimens with rock bridge angle ?1 and ?2 was studied.4.Specimen failure process was tracked by means of acoustic emission technology.and based on hit number.the fracture assessment method of crack extension and the stage characteristics were put forward.such as using linear crack stress,damage stress calibration.comparing the similarities and differences of hit rate change of specimen with single fracture under no-water condition and hydraulic coupling condition respectively.Simultaneously,the change of the characteristic stress of the specimens with double cracks and multi-cracks and the impact change rule of the joint expansion process between the multi-cracks under the specific rock bridge angle were studied.Based on the main frequency of acoustic emission,it is found that different fracture states of the specimen show different characteristics of main frequency.According to the change of the proportion of relative low-frequency signal and high-frequency signal,the fracture state of the specimen is predicted,and the early-warning information of specimen fracture under the condition of hydraulic coupling is put forward.5.Based on flat joint model of PFC numerical analysis software,simulation of crack initiation,extending,and the whole process of the failure of specimens containing 3D single,double,multiple cracks under different conditions was done,crack initiation mechanism was analyzed from the angle of the micro crack,the similarities and differences of indoor experiment and numerical simulation results were compared and the feasibility of the numerical model was studied. |
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