Limit Analyse And Large Deformation Consolidation Analysis By FEM For Soil Nailed Structure

In these years, more and more soil nailed retaining structures have been used in foundation pit excavations. However, the relevant theoretical study on such retaining structure lags far behind the engineering practice. For example, refer to Finite Element Analysis of soil nailed retaining structure, whatever regard it as a plane problem or a spatial one, almost all the computations are based on the assumption of small deformation without seepage and consolidation. In fact, large deformation often occurs in excavation retained with soil nailed structure in soft soil area, and the construction needs usually a period of time. Therefore, it is more reasonable to consider effects of seepage and consolidation as well as large deformation in Finite Element Analysis of soil nailed retaining structure.In this dissertation, on the basis of the studies so far available, the behavior and mechanism of the soil nailed retaining structure are systematically studied by limit analysis and by FEM considering large deformation, seepage and consolidation, and some valuable conclusions are obtained, which can be taken as references in practical design and construction. The main work is as follows:1. Based on energy method and power equilibrium equation, the formula of limit excavation depth of soil-nailed retaining structure Hu was derived, and new safety factor of each step k and each step depth A/z, were also obtained. Meanwhile, theconcept and the formula of pseudo-cohesion AC were proposed to simulate the reinforcement effect of soil nails. Moreover, the influences of soil properties and the geometric parameters of soil nails on Hu, k, â–³hi and â–³c were investigated.2. The Finite Element Formulation was derived for 3D large deformation consolidation of saturated soft soil with the description of U.L method. Also done was the Finite Element Formulation for soil nail element with both the descriptions of U.L method and T.L method. These make the theory of FEM more perfect ingeotechnical engineering analyses.3. Based on the theory of FEM of large deformation, the software ABAQUS was used to analyze the deep excavation retained by soil nailed structure, in which the coupled consolidation of soil with seepage and large deformation was considered. The variation principles of horizontal displacement of the structure, lateral displacement of surrounding soil, settlement of ground surface, heave of pit base, stress of soil nails and pore pressure, as well as the time effect induced by excavation and seepage were investigated. The influences of geometric parameters of soil nail, such as nail length and vertical spaces, and the properties of soil, such as permeability and compressibility, on the behavior of soil nailed retaining structure were also studied. The all results were compared with the ones obtained from the theory of FEM of small deformation.4. A practical excavation with soil nailed retaining structure was analyzed by FEM, and the results were compared with the measured ones from field observation. The good agreement validates the reasonability of the analysis considering coupled consolidation and large deformation.