The Critical Technology Research Of Modeling Theory And Stability Judgement In Deep Foundation Pit

For the critical problems in the foundation-pit, the corresponding solutions are indicated from several aspects, i.e. the model of foundation-pit numerical value simulation, back-analysis, stability, critical target of the foundation-pit strain. When the excavation of deep foundation is simulated in three-dimension with isoparametric elements which have eight nodes, the result is difficult to reflect the influence of bending-strain exactly because of the model itself. Therefore the safety of the project is threaten. In order to simulate the excavation more exactly, a model, which can not only improve the precision but also predigest the coupling of the different structure, is urgent to be established. This paper proposes one new elements - RH8 elements(Rotation Hexahedron element of 8 nodes). The determined finite element formula and random finite element formula of the new element is also presented. Then the new model of the foundation which give facilities for the finite element numerical simulation is developed. Ultimately, the dynamic simulation and stability of the foundation is studied. The main contents of the dissertation are as follows:1. Based on the inconsistent element theory and the Reissner variational principle which is modified to the independent rotation fields, the rotation degree is considered as independent degree and a new three-dimensional eight-node element-RH8 element is developed. Then the finite element formula is presented based on the variational principle. Finally this paper discussed the appropriate range of the new element.2. The new element is introduced into the problem of composite structures in which the girder, plate and block exists at the same time. Then this paper discussed the advantages of the elements when dealing with the connect problem. Ultimately, a classical problem calculating connect structures demonstrated the new elements is rational.3. The random variational principle with independent rational degree is proposed. Then on the basis of it, the random finite element formula of the new element is presented.4. This paper simulates the continuous wall, supports and soil mass adopting the new elements. Then it established a new model for simulating the excavation and discussed the existing issues, then gives some advices to this problem.5. The method of back-analysis and the existing problem is comprehensively summarized. This paper proposed the method of back-analysis with Parallel-Genetic-Algorithm and corresponding program has been validated correctly.6. Based on the Inteference-Energy method and Over-deformation method, the extensive angle method is applied in the judgement of the stability of ground foundation pit. At the same time, considering the uncertainty of the parameters, a system reliability method of the supports whose performance function is the inteference energy is presented. And the stability of the foundation is evaluated based-on the reliability method. Finally this paper bring forward the method to attain the critical target of the strain7. For certain project of deep foundation, stress-deformation analysis, soil parameters back-analysis, system reliability analysis of the support and the evaluation of the stability are done. The result is demonstrated rationally.