Deep Pit Space Co-deformation Method

Foundation pit projects become increasing popularity and their excavation depths become more and more deeper with the fast development of the high buildings and the wide utilization of the underground space. In consideration of most of the foundation pit projects are focused in cities, their construction fields are usually limited and the conditions are very complicated, therefore, how to guarantee the stability of the foundation pit is a valuable research field in practical area.On the basis of the sufficient consideration of the interactions and mutual deformations among retaining structures, brace structures, ring beam, middle beams and foundation soil in the deep foundation pit system, the spatial mutual deformation analysis method for the deformation and stability analysis of deep foundation pit is proposed with the Finite Element Method. The main characteristics of this method are as follows:1. The initial data for the calculation are automatically input and the corresponding subroutine is programmed.2. The state, distribution and value of the earth pressure acted on the retaining structures, which are the key factors that affect the deformation and stability of the deep foundation pit, are determined with the actual displacement caused by the interactions and mutual deformations of the retaining structures, ring beams, middle beams and the foundation soil without any hypotheses. Obviously, this method is more close to the practice than other methods.3. The real-time and dynamic simulations for the excavation processes and the setting of the braces and middle beams can be achieved with this method. What's more, the spatial dynamic change and distribution of the internal forces, displacements and the earth pressure acted on the retaining structures can be also described by the same method.4. The spatial change of the geological conditions can be considered by this method. The factors affecting the spatial effects of the deep foundation pit are researched indetail with the mutual deformation analysis method. These factors include the plane dimensions of pit, ring beam, middle beams, corner braces, embedded depth and brace stiffness. The results are compared with those of two-dimensional analysis, and theirdifferences and adaptability are clarified. Excavation processes of pit are simulated and the change of earth pressure, displacements and internal forces of the retaining structures during the procedures are discussed.Combined with the geotechnical engineering back-analysis theory, the displacement back-analysis method, which is based on the spatial mutual deformation theory, for deep foundation pit is also built up. Soil parameters can be back-calculated timely with the observed displacements and used to forecast the internal forces and displacements of the retaining structures in the next construction stage. The spatial mutual deformation back-analysis method brings an advanced solution for the analysis of the deep foundation pit stability and improves the level of construction informatization. At the same time, the uniqueness of the back-analyzed parameters is discussed.Correctness and suitability are proved by the comparison the calculated with observed results through the practical foundation pit projects with different retaining structures.The corresponding Fortran programs are designed for the mutual deformation analysis methods proposed in this paper.