CT Testing Analysis And Theoretical Study On Propagation Of Penny Shaped 3-D Fractures Under Compression

It is important that 3D constitutive model of jointed rock mass is established based on experimental results and theoretical analysis. The dissertation focuses on the study of fracture propagation mechanism of the similar rock material, which is carefully selected by comparison of similar physical and mechanical parameters. In the study, the CT real-time scanning tests of the specimens with manmade single or dual fractures has been carried out to understand the mechanism of the 3D fracture under compressive stresses.The length of wing crack of 2D and 3D fracture propagation under compressive stress will be obtained by theoretical analysis. Furthermore, the most likely propagation of fracture is suggested from inclined angle. The relationship between the angle of fracture and the ratio of initial fracturing stress to the peak stress will be obtained by uniaxial and triaxial tests. The stress distribution near the fracture of the specimens with single fracture under uniaxial and triaxial tests has been simulated using the numerical code FLAC3D. The results help to explain the CT real-time scanning tests results and the deduction of the constitutive relationship.The general propagation law of fractures and initial propagation strength, length of wing crack and the self-similar propagation length of crack are obtained from the CT real-time scanning tests of uniaxial compression. According to the longitudinal split scan images of the specimens prefabricated with single fracture at different angles, it can be concluded that the fracture propagation modes depend on the initial angle, length of the fractures etc al. The test results of specimens with dual fractures under uniaxial compression show that when rock bridge length approaches to the 4 times of the facture radius, the interaction between the dual fractures can be omitted. The test results with single fracture under triaxial compression show that the propagation of wing crack is restricted and the self-similar propagation is enlarged by comparison with the uniaxial test result. Furthermore test results show that the mechanism of the dual fracture propagation under triaxial compression is actually the overlap of the dual fracture propagation mechanism under uniaxial compression and the fracture propagation mechanism with a confining pressure.With the consideration of damage mechanisms of initial damage, fracture closure, self-similar propagation, friction sliding etc al, the 3D effective flexibility tensor and the brittle-elastic fracture damage constitutive model have been achieved. In the stability analysis of Xiamen subsea tunnel, comparing with the numerical results of FLAC3D and the 3D brittle-elastic fracture damage model of jointed rock mass, it shows that the developed model is more suitable for practical rock engineering.