Compression Failure Mechanism And Experimental Study Of Granite With Prefabricated Flaws

Under the influence of long-term geological movement and weathering,there are a lot of joints,fissures,holes and other defects in natural rock mass.Under the action of excavation load,the cracks are easy to sprout,expand and connect,which leads to the instability of rock mass and the disaster of rock engineering.Therefore,it is of great significance to study the crack evolution law and crack stopping and reinforcement method of fractured rock mass.Based on this,this paper combined theoretical analysis,laboratory experiments and numerical simulation methods to study the mechanical properties and compression failure characteristics of prefabricated fractured granite specimens,and also studied the effect of flaw fillers.The main work and conclusions of this paper are as follows:(1)Three mixed-mode fracture criteria of rock fractures are summarized,and the interaction mechanism between filling and fracture is deduced based on the interface contact theory.The theoretical analysis results show that the filling material bears a certain load through the interface contact between the flaw and the interface,reduces the stress intensity factor at the flaw tip,improves the stress state at the flaw tip,and thus delays the cracking.(2)The strength characteristics,failure process and flaw tip strain of the specimen with prefabricated flaws were analyzed by uniaxial compression test.The results show that the strength of the specimen is obviously weakened by the prefabricated flaw,and the smaller the flaw inclination angle is,the more obvious the weakening effect is;The propagation and penetration of the crack from the prefabricated flaw lead to the failure of the crack specimen;With the increase of the flaw inclination angle,the crack initiation and transfixion stress of the specimen increase,and the failure mode of the specimen is gradually changed from tension crack controlled failure to shear crack controlled failure.(3)Uniaxial compression tests were carried out on three kinds of fracture-filled granite specimens to explore the effects of different filler properties on the mechanical properties and failure characteristics of fractured granite specimens.The final results show that the filling material in the flaw can significantly delay the cracking of the specimen and improve the strength of the specimen.The specific filling effect is related to the material parameters of the filling material.When elastic modulus and strength of the filler become larger,the bearing capacity and the filling effect increase;The filling effect is also affected by the inclination angle of the flaw,and the effect of the filler decreases with the increase of the inclination angle of the flaw.(4)The RFPA software was employed for numerical simulation verification of the above experiments.The compressive failure characteristics and mechanical properties of fractured specimens with different filling states analyzed by RFPA were in good agreement with the actual data.In addition,RFPA is also used to analyze the influence of the parameters of flaws and fillings on the mechanical properties and stress state of the specimens.The results of parameter influence analysis show that,with the increase of the flaw length and width,the stress concentration at the flaw tip is more obvious and the peak strength of the specimen decreases;The stress concentration at the flaw tip is eased,and the peak strength of the specimen increases with the increase of the elastic modulus of the filling material;With the increase of filler strength,the stronger the bearing capacity of filler,the higher the peak strength of specimen.