Study On The Fracturing Algorithm Of The Discontinuous Deformation Analysis Method

Numerical simulation of rock mass failures is a hot topic in computational geotechnical mechanics.The fracturing of continuous rock is an important form of rock mass failures.In this thesis,the fracturing failure of continuous rock is simulated by the Discontinuous Deformation Analysis(DDA)method.A new DDA fracturing modeling algorithm is studied and developed.First,a meso-heterogeneity model is introduced into the DDA to simulate the fracturing failures of heterogeneous rock medium.It is found that,as in the original DDA sub-block artificial joint fracturing algorithm cracks can only occur along pre-set artificial joint surfaces,the fracturing simulation results are obviously affected by the mesh,and the calculation efficiency is quite low.T herefore,a new fracturing modeling algorithm,namely,the DDA sub-block element fracturing algorithm,is developed,which allows cracks to pass through sub-blocks.The specific research work is generalized as follows:(1)To simulate the fracturing failure of rock materials more realistically,based on the Weibull distribution function,a rock meso-heterogeneity model considering the heterogeneity of elastic and strength parameters is introduced in the DDA.The DDA sub-block artificial joint fracturing algorithm is adopted to simulate the Brazilian splitting test and the rectangular specimen uniaxial-compression test of rock.With the heterogeneity model the simulations derive macroscopic non-linear mechanical responses of rock with a meso-scale linear elastic constitutive relationship.Thereafter,the failures of center notched disk and rectangular specimens are modeled and discussed.(2)In the above modeling work,it is found that since cracks can only develop along the pre-set artificial joint surfaces,real crack paths can only be approached by crack bands,thus enough-small sub-blocks are required to reduce the influence of meshing on the crack path,which results in a low computation efficiency.Therefore,the DDA sub-block element fracturing algorithm in which cracks can pass through sub-blocks is developed.To realize this new fracturing modeling algorithm,preparation work including adding points to the initial model,searching loops of discontinuous surfaces and defining crack tips is conducted first.Then,the sub-block element fracturing is judged based on a modified Mohr Coulomb criterion.Finally,new sub-blocks are generated followed by the update of the stress,strain and contact informations of sub-blocks.The corresponding program code is dev eloped.(3)The classical tests of Brazilian splitting disk and split Hopkinson bar are simulated by the new fracturing algorithm.The simulation results are in agreement with the corresponding theoretical results and experimental results.The feasibility of the new DDA fracturing modeling algorithm is verified.As compared with the DDA sub-block artificial joint fracturing algorithm,crack paths in the new algorithm no longer need to be approximated by crack bands.The influence of mesh on fracturing modeling results is reduced,and a smaller sub-block number is required.Consequently,the crack path derived by the new algorithm is more accurate and the computation efficiency is higher.(4)The DDA sub-block element fracturing algorithm is applied to mode l the fracturing failures of rock.The failure of three point bending beam,rectangular samples under tensile and compressive loadings,and rock mass slope are numerically simulated and analyzed.The results show that the DDA sub-block element fracturing algorithm can solve the problem of crack initiation and propagation in rock better.This new fracturing modeling method provides an effective approach to solve practical rock mass failure problems.