The FEM Simulation And Analysis Of The Groundwater Control Of The Deep Foundation Pit

Deep foundation pit engineering,which covers several disciplines such as geotechnical engineering, structural engineering, hydrogeology engineering, geology engineering etc, which always appears as a temporary project but it costs 1/3 of all the project investment, is a comprehensive and complicated system engineering. As we have known, 80% accidents about pit are caused by the improperly processing of the groundwater, and have great impact on the social and bring much economic loss to the country. Therefore, to fully understand the impact on the foundation pit originated from seepage during foundation pit engineering, and to resolve the problem caused by the phreatic water and confined water around the support structure, is the definitely critical to perfect the design of foundation pit.The pit construction is simulated using the finite element analysis in this paper in order to analyze the soil seepage and solve a series of problems appears in the pumping water process. The Hardening-Soil constitutive model, which is well agreement with the actual condition, is introduced into our work. The stepwise pumping water in the construction period is simulated according to the variation of the draining level, meanwhile the drop-down depth of the confined water is simulated by controlling the draining volume of the local pumping. The distribution of water- soil pressure imposed on the support structure as pumping confined water, the land subsidence around the pit, as well as the deformation of underground pipe network and the buildings is clearly investigated by simulation. And to correct the error appears in the prevailed design process, which is the disbalance of water pressure under the wall as considering the soil and water separately. Different pumping water measures are proposed to guarantee the operating of underground buildings. On the recalculation of seepage stability, the more reasonable calculating method of safety coefficient of anti sudden-surge is submitted through theoretical analysis and case study simulation. Finally, the above-mentioned aspects are contrastive analyzed by introducing the actual project.The project calculation shows that the stress on the support structure is changed due to the seepage of groundwater; moreover, the change of seepage field will lead to the further change of stress if the confined water in the pit is pumped-out. At the same time, the stress field and the displacement field of the soil around the pit are changed due to seepage. Contrast to the presently design method, the deformation of support structure and the disbalance land subsidence outside the pit would increase if the seepage is taken into account, which is in agreement with the theoretical analysis. The deformation of support structure and the differential settlement problems can be resolved if the other measures are taken, and would in meet with the stability requirements.