| Composite soil nailing overcomes the limitations of ordinary soil nailing, and gets more and more applications in the construction of deep excavation because of the characteristics with economy, reliability, and fast and high effectiveness. However, at present the theory research of composite soil nailing is far behind from the engineering practice. The main difficulties that apply FEM to supporting projects depend on choosing a suitable model and parameters. The actual projects is as a basement of studying on the key issues in simulation technology, integrating practice measured data with numerical simulation, and analyzing deformation and mechanical characteristics of support engineering with FEM. There are great significance in theoretical research of soil nailing, as well as selection and technologial demonstration of supporting scheme.The peper summarizes the research results of predecessors on the field of soil nailing, selects the appropriate parameters, establishes FEM, puts numerical simulation in practice and compares simulation and test results. The composite soil nailing technology of deep excavation is discussed that based on one excavation in Beijing Metro Line 10. The major innovation of this sdudy is as follows:(1) The research results of predecessors in the field of soil nailing are inspect and summarized. The soil model of Drucker-Prager is adopted as the constitutive model. Through the establishment of"point–surf"contact pair and choosing the suitable unit parameters, the contact state of soil body and soil nails, anchor segment is simulated. Contact of soil and surface layer is simulated with constraint equations. Software ANSYS "Reading" and "write" initial strain function is used in achieving the input of initial stress of soil. The prestress input of bolt and soil nails is achieved by giving initial strain to bar elements when they are defined. These are very important in the effectiveness of simulation, and the researches contribute to the development of simulation technology.(2) The paper establishes model with ANSYS software, simulates and analysis the deformation characteristics of the actual projects under different working conditions. The research shows that the ordinary soil nailing imposed appropriate prestress witch can reduce the horizontal displacement of pit. There is a certain coupling relationship between horizontal displacement of slope and pit uplift, and prestress soil nailing programme is technically feasible. The research provides the basis for the choice of support programme for the actual works. The programme can reduce the construction cost.(3) The resarch simulates distribution and change the characteristics of supporting structure internal forces and the effect of prestress factors. The prestressing anchors should be set at 1/3 H (depth of pit), and it can effectively reducing the horizontal displacement of top and middle of the pit as well as play the best supporting role. The force of soil nails has effect of excavation. In excavation works, soil nails should be installed in time in order to play the role as soon as possible, and reduce deformation of excavation pit.(4) The study on techniques of construction and monitoring data shows that deformation of excavation pit is in the valueable range, the deformation and mechanical characteristics is as the same as the simulation results. The surface subsidence and growth of soil nailing internal force are concentrated in the excavation phase, The most dangerous period is in the excavation stage, and for surface subsidence the most dangerous areas of is within 1-1.5 times the depth of pit...
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