Three-dimensional fracture evolution patterns of rocks under true triaxial conditions based on real-time CT scanning

The real-time and accurate grasp of the internal fracture expansion and evolution law in the whole process of rock failure is of great engineering significance for scientifically guiding the stability control of underground rock engineering and promoting the safe mining of mine resources A set of true triaxial loading test equipment that can be matched with the CT scanning system has been developed The equipment components located in the CT scanning area are designed with new carbon fiber materials,including core components such as vertical loading system,lateral loading system,true triaxial pressure chamber,etc,so that X-rays can effectively pass through the pre-designed CT scanning area in the device The function of real-time CT scanning under true triaxial stress environment is realized This equipment was used to carry out real-time CT scanning tests of intact rock and rock with fractures under triaxial different stress conditions,and obtained the rock stress-strain curve during the entire loading process The spatial three-dimensional CT characteristics of the internal cracks in the rock under different working conditions are obtained,and the results show that:compared with the complicated spatial expansion of the internal cracks in the rock under the CTT condition,the spatial morphology of the internal cracks in the rock under the TTT condition is simple Plane cracks It shows that under true triaxial conditions,the internal fractures of the rock have a clear expansion direction (expanding along the σ2 direction)Four initiation cracks appeared in the rock under the two conditions of TTT-c2 (with cracks along the σ2 direction) and TTT-c3 (cracks along the σ3 direction)However,the initiation cracks of the former are all coplanar initiation cracks with the front edge of the pre-crack,and the pre-crack surface remains basically intact;the latter are all perpendicular to the front of the pre-crack,showing a trend of transversely cutting the pre-crackEventually a complex network of fractures was formed,resulting in more prefabricated fractures and backlog damage Under the three working conditions of true triaxial,all the crack inclination angle distributions are extremely concentrated,which are roughly parallel to the σ2 direction It shows that the intermediate principal stress plays a decisive role in the propagation direction of initiating cracks in the rock,and the propagation and development process of the internal rock cracks strongly depends on the direction of the intermediate principal stress.