The Discontinuous Deformation Analysis Considering The Block Internal Coupling Effect And Plastic Anchoring Effect

With the surging development of economic construction and large-scale water conservancy and hydropower engineering in China, large discontinuous deformation theory and computing of rock has become the focus of academic research. The discontinuous deformation analysis of block systems (DDA), as a new numerical method developed in the past thirty years, is able to mirror the discontinuity of rock mass deformation while satisfying the fundamental equations of the elastic theory. The DDA method has promising prospects in engineering application, thus being one of the research hotspots in geotechnical engineering. However, the DDA method still has some limitations in engineering applications. In this thesis, the discontinuous deformation analysis method is improved by taking into account the displacement convergence criterion and the plastic deformation of bolts. Besides, the coupling of DDA method and finite element method is established and parallel algorithm of DDA is also discussed. Eventually, the DDA method is applied in the project of Sichuan Badi Hydropower Station, in which the determination of equivalent mechanical parameters and the dynamic construction process are mainly studied. The main contents of this thesis are listed as following:1. Adopting the discontinuous deformation analysis method, the uniaxial and biaxial compression experiments of double-fractured rock mass were numerically simulated. Influences of different fracture angles and lateral stresses on the behavior of rock mass under compression tests were studied and the corresponding stress-strain curves, together with the crack initiation stress and the peak strength of specimens were obtained. In the biaxial compression experiments of double-fractured rock mass considering different lateral pressures, the strength envelope diagram of45°fractured specimen were obtained. The parameters obtained from the biaxial compression experiments were used in a practical engineering example and the different damage states of intact rock and fractured rock were analyzed after excavation of underground caverns by means of the equivalent continuum method. Nevertheless, the plastic deformation mechanical model of anchor was added in the program of DDA. With this improvement in program, the axial load-displacement curves and the crack propagation process of different anchored-fractured specimens were obtained, which means it could simulate the anchorage effect on fractured rock. The simulation results and the previous splitting tests under similar conditions agree well with each other. At this point, the improved program showed its ability to provide better description of the anchor bolt stress.2. Parametric design language APDL was applied in the interface program development of discontinuous deformation analysis and ANSYS calculation program, which greatly facilitates the pretreatment process. In the meantime, the general balance equations of the method that couples the DDA and ANS YS were deduced in the linear displacement mode, and the corresponding elastic matrixes, inertia matrixes, load matrixes and contact matrixes were also deduced in details. After coupling the two methods, the freedom degrees of each block are determined by the number of nodes, thus being able to more accurately describe the deformation of blocks. Finally, factors that impact on the displacements of an underground cavern were analyzed employing the coupling method, from which it was concluded that the lateral pressure coefficient, rock crushing surface cohesion, internal friction angle and tensile strength have larger effects on the stability of the surrounding rock mass. In addition, the top arch of the cavern was the key position for supporting arrangement in this project, providing reference for the engineering.3. The parallel algorithm based on OpenMP method was considered in the DDA program and the parallel assembly strategy of stiffness matrix was put forward. The calculation of the DDA equations was conducted with the modified SSOR-PCG method in order to improve the calculation efficiency. Finally, it was proved by calculating numerical examples that the modified parallel algorithm can significantly enhance the rate of calculation.4. In the practical application of engineering, the Badi Hydropower Station, mechanical parameters of the DDA were determined through field test data and numerical simulation, considering the randomness of rock joints and the uncertainty of rock mechanical parameters. Dynamic construction process is studied in this engineering while excavation sequence, step-by-step excavation and supporting process were specifically analyzed.5. The coupling problem of the discontinuous deformation analysis method and the finite element method, the dynamic construction process of excavation and the step-by-step support problem were tackled through numerical simulation carried out based on OpenMP parallel algorithm. The plastic deformation model of anchor bolts and the displacement convergence criterion were added to the DDA source program, through compiling calculation program in VC++platform with C++language. Last but not least, this program could potentially provide a better analysis of block deformation and engineering application.