Yuki Imai

Numerical Simulation of Dynamic Fracturing Using a Particle Method

Better understanding of failure mechanism of rocks benefits in many fields from rock engineering to earth sciences. Especially, it is essential to understand how fractures initiate and propagate under various loading conditions in order to clarify real rock fracture processes. For the interpretation of rock failure, many attempts have been made experimentally or using fracture mechanics theory. Although much of the knowledge available today is based on experimental observations and the theory successfully represented the propagation of predefined cracks, the failure mechanics are not fully understood by experimental results and it is difficult to describe the initiation and coalescence of cracks using the theory. Thus, in the recent years, numerical modeling, which may be less restrictive, has been applied to study crack behaviors, and we also approach to the rock failure based on numerical simulations. To represent rock failure, we use a Hamiltonian Particle method (HPM), one of particle methods. In the HPM, we do not need to use grids or meshes to discretize the rock model, and thus we could deal with the failure relatively easily. In spite of this advantage of the HPM, the applicability of the method to the failure phenomena have yet to be revealed fully. In the present study, we apply the HPM to rock failure under some different specimens and different loading conditions. As a result of our simulations, the HPM successfully reproduce failure pattern of brittle fracture observed rock fracture experiments and can observe micro cracks initiation and propagation. This suggests that the HPM is the useful tool to analyze rock failure.

Relationship between Parallel Faults and Stress Field in Rock Mass

Parallel cracks and faults, caused by earthquakes and crustal deformations, are often observed from regional to laboratory scales. However, the mechanism of the formation of these parallel faults has not been quantitatively clarified, yet. Since the stress field plays a key role in the nucleation of parallel faults, it is fundamentally to investigate the failure and the extension of cracks in a large-scale rock mass (not with a laboratory-scale specimen) due to mechanically loaded stress field. In this study, we developed a numerical simulation code for rock mass failures under different loading conditions, and conducted rock failure experiments using this code. We assumed a numerical rock mass consisting of basalt with a rectangular shape for the model. We also assumed the failure of rock mass in accordance with the Mohr-Coulomb criterion, and the distribution of the initial tensile and compressive strength of rock elements to be the Weibull model. In this study, we use the HPM (Hamiltonian Particle Method), one of the particle methods, to represent large deformation and the destruction of materials. Our simulation results suggest that the compression field have dominant influence for the initiation of parallel faults and their conjugates propagate in uniaxial condition. We conclude that the shearing force would not provoke the propagation of parallel fractures.