| A lot of bolts and shotcrete lining are applied to reinforce jointed rock masses in geotechnical engineering. The analysis of jointed rock masses reinforced by bolts and shotcrete lining is very important to the engineering. Generally speaking, the equivalent model and the explicit model have been proposed to study jointed rock masses reinforced by bolts and shotcrete lining. They have their own merit and shortcoming:using the former, the behaviors of all of the components can be well simulated, however, much preprocess work is needed; the latter has the little limit in preprocess, but it cannot have very detailed simulation of the components. So, equivalent model are applied to simulate great quantities of joints or fissures, shotcrete lining and system bolts. As to the larger faults and important shotcrete lining and bolts, explicit simulation is usually proposed. As the scale of geotechnical engineering is greater and greater, more and more complicated geology condition including many faults, shotcrete lining and bolts is to be treated. It is very difficult to simulate all important faults, bolts, and shotcrete lining explicitly. Even worse, when the configuration of a structure is modified, it will cost much time and manpower to remesh. Combining the merits of the two models, the composite element method (CEM) is proposed to explicitly simulate jointed rock masses reinforced by bolts and shotcrete lining, which transfers the difficulties in preprocess into computation and heightens the efficiency.Comprehensive researches of jointed rock masses reinforced by bolts and shotcrete lining are conducted in this dissertation on the basis of CEM.Firstly, a review of ground anchorage and bolts and shotcrete lining support is made, and the working characteristic and action principle of bolts and shotcrete lining support is present in this dissertation. For bolts and shotcrete lining support, it has the characteristic of betimes, cohesiveness, deeply, flexible, adaptability to change and sealing which composite the basic elements of using the strength and self-support of surrounding rocks completely. During the long-term application of anchorage technology, several theories such as suspension theory, combined beam theory and combined arch theory have been proposed and generally accepted. Based on them, new theories including maximum horizontal stress, surrounding rock strength intensify theory, surrounding rock loosening circle and the full-length anchoring neutral point theory etc. have been present recently.Secondly, method and status of recent research about jointed rock masses and anchorage has been summarized. Physics experiment method, engineering analogy and numerical analysis are the mainly used methods on jointed rock masses anchorage. The theory system about anchorage is divided into discontinuous medium mechanics discrete method and continuous medium mechanics equivalent method. The former includes limited equilibrium theory (LET), key block theory(BT), discrete element method (DEM), discontinuous deformation analysis(DDA), block element method and interface element method. Finite element method (FEM), boundary element method and fast Lagrange analysis of code (FLAC) are attributed to the latter. Recently, methods combined of their characteristics are proposed taking the numerical manifold method (NMM), mesh free method (MFM) and composite element method (CEM) for example. All of their applications in anchorage theory are presented in the dissertation while emphasis on the CEM where its development course and basic theory are introduced.Thirdly, on the basis of CEM, the elastic composite element model for jointed rock masses supported by bolt and shotcrete lining is present in the dissertation. In this model, mesh can be generated without considering joint, grout, bolt and shotcrete lining firstly, and the elements containing them are defined as composite elements.8sub-elements are established to cover rock, grout, bolt, shotcrete lining and all interfaces. The displacements of the rock, grout, bolt and shotcrete lining can separately be interpolated from the sub-elements’nodal displacements. The interfaces have no independent nodes, and their displacements can be interpolated from the difference between the nodal displacements of rock, grout, bolt and shotcrete lining. According to the elastic constitutive relation and the virtual work principle, the equilibrium equation can be established. With the solved nodal displacements, the detailed behaviors of sub-elements can be described. This model can be incorporated into the conventional finite element analysis without any difficult. The conventional finite element can be treated as a degradation of the composite element. In the numerical example, elastic calculation for a jointed rock mass supported by grout-bolt and shotcrete lining is carried out by CEM and distinct element FEM. The comparison of the calculation results shows the validity of this model and the advantage of CEM in the pre-process of jointed rock mass supported by bolt and shotcrete.Fourthly, on the basis of elastic composite element model for jointed rock masses supported by bolt and shotcrete lining, an elastic-viscoplastic composite element is established. For every component, we use the elastic-viscoplastic constitutive relation to simulate the course of stress and strain changing with the time. In practical engineering, for the simple elastic model, it cannot show that the stress and strain of rock is changing with the time, so it cannot simulate the actual process of stress-strain of jointed rock mass. The elastic-viscoplastic model can solve the problem. In the numerical example, with the same model as elastic calculation, elastic-viscoplastic calculation is carried out by CEM and distinct element FEM. The comparison of the calculation results shows the validity of this elastic-viscoplastic model.Fifthly, the P-version adaptive CEM for jointed rock masses supported by bolt and shotcrete lining is proposed in this dissertation. With the simple preprocess, CEM has many advantages to simulate the complex structures. Using linear shape function as conventional FEM, CEM will have some difficulties in describing detailed nonlinear mechanical characteristics of complex structures under a low density of mesh. Generally speaking, increasing the density of the mesh is usually proposed to solve the problem. But it will increase the difficulties of preprocess. Furthermore, this approach disobeys to the CEM principle of simple preprocesses. To more complex mechanical characteristics of jointed rock masses supported by bolt and shotcrete lining, the linear shape function of conventional CEM has more difficulties to make a detailed simulation under a coarse mesh. Thereupon, P-version composite elements are defined to describe the jointed rock masses supported by bolt and shotcrete lining in this study. With the hierarchical basic function upgrading, the displacement mode of jointed rock masses supported by bolt and shotcrete lining and mechanical characteristics of all of the sub-structures can be well simulated by P-version CEM in physical hypostasis. Equation formulated, the method proposed can be realized in the program. The actual effect is shown through a comparison of calculation results among P-version CEM, conventional CEM and conventional FEM for an example.Finally, the study present above is applied onto the underground engineering of Pubugou powerstation. With the3dimensions calculation meshes of CEM and FEM, the engineering is analyzed separately by CEM and FEM. The mesh of CEM which contains12311elements and12429nodes is generated without considering the grouts, bolts, shotcrete lining, joints etc. With a mesh containing73788elements and98188nodes, the distinct model is applied into FEM calculation. In the study, excavation is divided into9steps and reinforcement is applied after every excavation step. The comparison of the calculation results shows the advantage of CEM in preprocess and the preciseness of CEM in distinct simulation.With a good foreground in the engineering, the study of CEM for jointed rock masses supported by bolts and shotcrete lining has been achieved, but many problems need to be solved to improve them, yet. Crack analysis, dynamic analysis, thermal analysis, localization analysis, coupling analysis, etc, are all the fields where CEM can show its advantages. |
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