The Deformation Characteristics Analysis Of Deep Foundation Pit While Dewatering And Excavation Considered Simultaneously

Deep excavation is a complicated systematic project, in high water table areas, dewatering, excavation and support bring the changes of seepage field and stress field, with mutual action of seepage field and stress field, they together control the deformation of the foundation pit. But the current study of deep foundation pit are mostly confined to a separate analysis of seepage problems or excavation problems, the deformation characteristics of deep foundation pit can't be truely reflected. Therefore, the simulation of the dewatering and excavation process and the analysis of the deformation properties have reslistic significance.Based on the Biot consolidation theory and FEM theory,the coupled analysis method in deep excavation analysis was presented. The steady analysis and transient analysis methods were respectively used for Two-dimensional coupled analysis of a basic foundation pit example. The parametric analysis for transient analysis method found that: the water level drawdown increased linearly with the increase of well points number and the flow rate, while it increased with the decrease of soil permeability. The the greater soil permeability coefficient was, the greater flow rate for dewatering was needed, and the longer time for the stability of groundwater seepage was spent.The steady analysis model is applied to 500 kV Shanghai Expro underground Substation foundation project. Through the deformation characteristics study, the follow results were found: during the dewatering period soil had a settlement, during excavation period soil had a upward rebound. The comparison of calculated results with measured data verified that the steady analysis methods are feasible and correct in such kind of projects.The transient analysis model is applied to the Shanghai Hongqiao transport hub's multi-echelon excavation project, the dewatering and excavation process were simulated based on the practical work. The flow rate and pumping time were defined to simulate the pumping process. The deformation and porepressure change characteristics study show that, while the wells were distributed in and out of the pit, the environment effect become greater, seepage field and stress field together controled the deformation. The comparison of calculated results with measured data verified that transient analysis methods are feasible and correct,which also have a a certain degree of theoretical and practical value.