Research On Internal Forces And Deformation Of Composite Soil-Nailing Of Deep Excavation Process

The composite soil-nailing method is a geotechnical comprehensive shoring technique combining soil nailing with other soil reinforcement procedure. It is a soil-nailing technique with Chinese characteristics developed during the deep foundation pit sheathing practice in urban districts in recent years. The technique has overcome the inherence defect of traditional soil nailing, and found broad prospects of application. Based on site conditions and geological conditions, various composite soil nailing structures can be used.The composite soil-nailing method has found wider and wider application in deep excavation in China because of its advantages, such as: safe and reliable, easy to implement and less investment. However, theoretical research on the technique has fall behind its engineering practice recently. Research on behaviors of soil nail and the reinforcement parts; Research on interaction between soil nail and soil; Research on interaction between reinforcement parts and soil; Research on internal force and deformation of the supporting structure are still in their initial stage. Research on working mechanism of the reinforcement parts in the composite shoring structure (except deep mixing pile) has even not started yet. Large-scale testing research on composite soil-nailing structure has very few researchers set foot in. Comprehensive and accurate experiments or field test data are rather limited.Research in this dissertation is expected to reveal the characteristic of internal forces and deformation of composite soil-nailing structure of deep excavation process, so as to provide scientific basis for its broad application. The research focuses of this dissertation are as follows:(1) Summarize the advantages, development, prospects of application and research present of composite soil nailing, through discussion, and analyses the deficiency of present research on the technique.(2) On the basis of analysis of working mechanism of all the parts of composite soil-nailing structure, a three-dimensional (3D) finite element model (FEM) has been developed take advantage of ANSYS 7.0. The Drucker-Prager model is chosen to analogy the nonlinearity and plasticity of soil. Soil and the deep mixing pile are simulated by 20 nodes solid element; soil nail, anchor rod, crest beam, waist beam and reinforcement are simulated by 2 nodes 3D beam element; the shotcrete slope face is simulated by 3 nodes 3D shell element; the adhere-slip behaviors between soil nail, anchor rod, crest beam, waist beam, reinforcement, shotcrete slope face and soil are simulated by contact element. The staged excavation and retaining can also be simulated in this model. An engineering case is, as an example, analyzed and predicted internal force and deformation of every parts of the composite soil-nailing structure at various stages of excavation.(3) Field tests of composite soil-nailing structure have been carried out in two foundation pits in Guangzhou, and abundant of data have been obtained. The comprehensive analysis of themeasurements further reveals the characteristic of internal forces and deformation of composite soil-nailing structure of deep excavation process, and provides practical data for the verification of design and theoretical analysis.Finite element analysis method have widely used to analyze geotechnical engineering problem as powerful means for simulated calculation, but not perfect yet, because of difficulty in the definition of constitutive model of soil and its parameters. However, the method is valuable in the analysis of working behaviors of geotechnical engineering structure, if an appropriate model is chosen. On the other side, a large number of data obtained through experiments and field tests will verify the reliability of finite element analysis, and calibrate the model parameters, so as to promote the development of finite element analysis method. The method not only can predict the internal force and deformation of soil, soil nail, shotcrete slope face and reinforcement parts in a composite soil-nailing structure, a...