Analysis And Research On The Behavior Of Foundation Pit Deformation With Considering Seepage And Multi-Stage Excavation

During the excavation of foundation pit, the seepage field and stress in the soil had changed due to the difference and variation of water head between the inside and outside of foundation pit, as a result, the interactions between seepage field and stress field are complicated. It has been shown by a great amount of practices that the influences of this seepage are obviously. However, there is very little relevant study so far.In this thesis, my study backgrounds are monitoring a pumping station and a square foundation pit. Based on monitoring data and the theory of seepage,2D Finite Element Method are used to solve the seepage equations, and did analysis and research on the behavior of foundation pit deformation with considering seepage and multi-stage excavation. The mainly contents and results of this thesis are as below:1. Monitoring work had first been carried out on pumping station which included collecting and analyzing datas of the horizontal displacement of pile peak, groundwater level, support axial force and deformation of supporting structure. The results showed that the monitoring method applied in this foundation pit had made great effect ,and it can be applied in similar conditions.2. In the applitication of FEM, the parameter refer to the soil must be carefully considered. The value of the parameters (including c,φ,E_s and k) were tested by laboratory soil test, basing on this datas combined with experiential value on the manual, the value are confirmed.3. FEM analysis on foundation pit is based on the examples mentioned above .The seepage was considered to be a variable factor. To study the distribution law of the seepage, 2D finite element analysis models that in no proe and pore were established. In this way, the behavior of foundation pit such as supporting structure displacement, the settlement deformation of ground and the upheaval deformation of land were analysised and researched,and it were compare with the data obtained from field observation. The behavior of foundation pit deformation on this condition were as follow: (1) The supporting structure maximum displacement in pore is 30% larger than that in no pore, and the result is similar to the value data obtained from field observation.(2) The settlement deformation of ground was developping during the stage of excavation, the maximum is in single excavatiom depth. The deformation in pore increased significantly,and the maximum displacement site outward movement.(3) The upheaval deformation of land showed as a parabola,and the maximum deformation site is in the middle of the bottom. While considering the influence of the seepage, it is larger than that in no pore and the maximum deformation site is on the side of bottom excepte the first step excavation.4. Base on the example 2,2D finite element analysis models in pore were established, seepage is considered to be constant .To study the behavior of foundation pit deformation by changing the soil parameters(seepage coefficient and angel of internal friction) ,It can be concluded as below:(1) When the seepage coefficient change within 1 to 10, it has few influence on oundation pit deformation but Seepage coefficient follow the foundation pit deformation changes as well. However, the upheaval deformation of land is in evidence by the chang of seepage coefficient,so as the bottom heave, especially on the place of supporting system.(2) The chang of internal frictiot had great effect on the behavior of foundation pit deformation. The displacement of supporting structure became larger as the angle of internal frictiot became smaller. The calculation value showed that: the angle of internal frictiot reduce 50 percent, as the displacement of supporting structure increace approximate 30 percent. The settlement deformation of ground and the upheaval deformation of land were also affected by the chang of seepage coefficient in evidence.