Three-Dimensional Failure Process Analysis Of Rock And Associated Numerical Tests

Rock failure process is a complicated non-equilibrium nonlinear progressive process with the evolution of associated cracks initiation, propagation and coalesces. Due to the heterogeneities contained in the rocks, it is difficult to describe the structures and components accurately. In rock failure process study, the formation and interactions between all kinds of weakness on different scales are so intricate that more work is paid attention to stress field investigation and failure criterions of materials.However, the investigation of fracture process is much more significant than stress field investigation. Since the first complete stress-strain curve was obtained by Cook in 1963, large numbers of rock failure experiments were undertaken to study the rock progressive failure process. The results showed that unstable point was found after the peak strength point in the complete stress-strain curve, and it explained that pillars or wall rocks had carrying capacity to some extent in mining engineering after their peak strength. The rocks or rock masses we encounter in mining engineering are not intact, and how to make most use of the residual strength of fractured rock masses to save support and excavation costs is much important than the acquirement of the peak strength of rock or rock masses.The problems in rock mechanics and engineering are all of three dimensions to some extent. Rock and rock masses composing the earth's crust are under three-dimensional stress condition, and fracture formation in rocks, including crack propagation, interaction and coalescence shows three-dimensional features. In geophysical studies, the distribution of faults and seismic evens are all three-dimensional. Many rock mechanical problems, except plain strain problems and plain stress problems, such as crack propagation and crack interaction are related to many directions and cannot be simplified to two-dimensional problems. Few presentations can be found to explain the progressive failure of rock in three-dimension and related nonlinear behavior resulting from material heterogeneities.On the one hand, it brings enormous difficulties to observe the three-dimensional fracture process in rocks, because of the non-transparency of rocks. Some transparent materials, such as PMMA or glass, used in experiments instead of rocks are homogeneous. Rocks belong to heterogeneous materials that contain micro cracks and flaws, and heterogeneity plays an important role in fracturing process. However, there are no proper approaches in mathematics to describe three-dimensional crack propagation even in homogenous material. On the other hand, artificial triaxial tests are undertaken in experimental investigations instead of triaxial tests, due to difficulties in rock sample preparation and the loading conditions. It has been approved theoretically and experimentally that the intermediate principal stress has great effects on rock failure process and the intermediate principal stress can not be considered in artificial triaxial tests.Numerical test provides an utmost means to study the failure process of rock-like materials. Finite element method is a useful and effective tool among various numerical methods to analysis the rock mechanical problems. However, the traditional finite element method should adopt new techniques and other methods to meet the need of mesomechanics. The traditional numerical methods are applied to get a satisfactory initial stress, initial strain fields or the final stress state. With the improvement of computing environment and the practical demands in rock mechanics, rock failure process analysis is turning its steps to...