Analysis And Research Of Groundwater Seepage Influence On Stress And Deformation Of Foundation Pit And Retaining Structure

Dewatering is necessary in the excavation under high groundwater level, which firstly provides a dry environment for the excavation and secondly reinforces the soil. But the seepage field and the stress field in the soil will change constantly as dewatering and excavating, and may even induce engineering failure. So it is very important to correctly analyse the seepage effect on the stress and deformation of foundation pit and retaining structure. The main research contents and results are as follows:1. Based on the testing tank model experiment and the triaxial compression test, the consolidation effect by seepage and dewatering on the soil is analyzed, the measured values of water and earth pressure acting on retaining wall under different conditions are compared with the theoretical values as well as. It is indicated that dewatering and seepage can increase the shear strength of the soil. The water and earth lateral pressure of the upper soil in the testing tank by calculating separately method is more rational, and the water and earth lateral pressure of the lower soil by calculating together method is more rational.2. Numerical analysis is executed to the 2# circular coal yard deep foundation pit of Jiangsu Huadian Jurong power plant by using the finite element software ABAQUS. In combination with the site monitoring date, the consequences with the consideration of groundwater seepage are contrasted to the consequences without the consideration of groundwater seepage including the deformation and stability of the foundation pit. The analysis indicates that the results with the consideration of seepage is relatively close to the site monitoring date. Compared with the results without consideration of groundwater seepage, when working to relative level 12.3m taking seepage into account, the surface subsidence 15m to pit wall sinks about 20mm. The horizontal displacement of the top ring beam increases about 1.5mm. The biggest springback deformation of the pit increases by about 21% and the maximum horizontal offset of the pile increases approximately 5mm. And the location of the maximum horizontal displacement moves two meters down. So seepage is harmful to the deformation of the foundation pit and the retaining structure, so should be considered in the design of foundation pit supporting.3. The changes of the deformation of foundation pit and retaining structure are analyzed by changing the seepage effect factors, such as the depth of dewatering well, the number of dewatering well, the buried depth of waterproof curtain, and the soil permeability coefficient.The results show that:(1) The deeper the depth of dewatering is, the lower the water level of both inside and outside foundation pit is, when reaching eventual stable level, thus increasing the surface subsidence outside foundation pit and reducing the horizontal displacement of the top ring beam. Uplift deformation of the pit bottom reduces, but the horizontal displacement of the top pile decreases and the horizontal displacement of the pile bottom increases.(2) The decrease in the number of dewatering well can minish the influence to the surface subsidence outside the foundation pit, but the lateral shift of the foundation pit and the upheaval deflection of the pit bottom are both enlarged. And with the reduction in the number of dewatering well, the lateral shift of the pile top will enlarge, and the lateral shift of the pile bottom will minish.(3) The deeper the embedment of waterproof curtain is, the high the water level outside the pit is, which is more beneficial to control the surface subsidence outside the pit. But the water level inside the pit reduces with the increase of depth of embedment. So water head difference between inside and outside the pit will be larger, which is not conducive to lateral deformation. It is harmful to the deformation of the foundation pit and the retaining structure.(4) With the soil permeability coefficient increasing, the lateral deformation of the pit wall just changes slightly, but the uplift deformation increases obviously, so the increase of the permeability coefficient is against the local stability of foundation pit. With the increase of permeability coefficient, the lateral displacement of the pile reduces.