Study On Numerical Methods For Modeling Failure Process Of Semicontinuous Jointed Rock Mass

The failure of rock mass is related to the generation, propagation and coalescence of interior cracks, so the study on the law of crack propagation is very necessary for uncovering the mechanism of rock failure and estimating the safety of rock structures. Owing to the mechanical and geometrical complexity of crack propagation, numerical simulation is the most effective tool among the available investigation approaches. However, the commonly-employed numerical methods can not simulate some phenomena in rock failure, such as new crack generation, crack branching, multi crack interaction etc. Against this background, based on the discontinuous deformation analysis (DDA) method, DDARF (discontinuous deformation analysis for rock failure) is proposed in this thesis.In the proposed method, the random joint network is produced in the area of interest by using Monte-Carlo technique. On the basis of the joint network, the triangular DDA block system is automatically generated by adopting the FE adaptive mesh generation technique—the advanced front method. To simulate the heterogeneity of rock mass, the randomly distributed mechanical parameters statistically satisfying Weibull's law are assigned to these blocks. In the process of generating blocks, numerous artificial joints come into being, and they provide the potential paths along which the cracks generate and propagate. The blocks between artificial joint are glued together by adhesive algorithm, and if the glue is invalid, the artificial joint will break and become real crack. In order to eliminate the effect of block boundary on crack propagation path, the fracturing algorithm within one block is established. In this way, the rock failure process can be simulated. Based on the proposed algorithms, the corresponding C++ program module is developed and incorporated into the original DDA code, i.e. the DDARF grogram. For verification, a series of numerical examples are computed to simulate the propagation and coalescence of the closed joints in different rock samples under different loading conditions. The simulated results agree well with the existing experimental and numerical results, indicating that the proposed algorithms are correct and valid. Finally, the rock failure process under more complex condition of some concrete rock engineerings is modeled. With the introduction of the artificial joint concept into the discontinuum-based DDA, DDARF can be applied to simulate the cases of continuum, semicontiuum, as well as discontinuum, without any mathematic difficulty. Moreover, it can easily simulate the generation, propagation and coalescence of rock crack, and the whole process of rock failure is thereafter reproduced.In addition, for modeling dynamic problems by DDA method, a new boundary condition, namely non-reflecting boundary or viscous boundary, is presented in this thesis. The approach is to attach the independent dashpots along the normal and shear directions of specific boundaries, in this way, the energy of stress waves can be absorbed efficiently when the stress waves reach those boundaries, and non-reflecting condition is achieved. The proposed viscous boundary condition is incorporated into the DDA code. To verify the effect of absorbing stress wave of viscous boundary, some examples are calculated, and the numerical results are compared with the test data. This work provides the fundamental for DDARF to simulate the dynamic failure of rock mass.