Study On Pit Angle Effect And Optimization Of The Pile-anchor Supporting System In Deep Foundation Pit

The pile anchor bracing system of deep excavation is a three dimensional space structure, but in the design of the supporting of the deep foundation pit, it is generally considered that the foundation pit is a two-dimensional plane strain problem. Its design calculation results are often obviously different from the result of actual. The reasons that result in these differences primarly due to the deformation of deep foundation pit has a significant effect on the three-dimensional space. It is reflected in the deformation of foundation pit varives with the relative of the slope angle of the pit. The deformation of foundation pit near the corner of the foundation pit is small and the middle of the foundation pit is larger. So the deformation of the foundation pit has the active earth pressure of corner effect.This paper is basic of the subject of the second phase of deep foundation pit engineering of residential area, Through the analysis of the displacement variation rule of the etaining structure and surrounding soil by the field monitoring and finite element simulation. It is proved that there is a significant pit angle effect in the construction process of deep foundation pit, the supporting structure is optimized in the influence range of the pit angle effect.The field test results are analyzed at first, the deformation laws of the horizontal displacement of the top of the crown beam on the north and south sides of the foundation pit and the settlement of the soil after the pile and the horizontal displacement are obtained. The horizontal displacement in depth variation of supporting piles and the soil behind piles in different positions of the pit angle is analyzed, the variation law of horizontal displacement of supporting pile and pile in different position of foundation pit is summarized. Through the comparison of the change law of the angle of the foundation pit and the middle part of the foundation pit, it shows that the angle effect of the foundation pit is in the pit excavation process.Then combined with the actual condition of foundation pit, MIDAS/GTS is used to carry out the finite element simulation, and the deformation data of the field is compared with the data of finite element simulation, which proves the rationality of the model. Then the change rule of the horizontal displacement of pile in different position from the corner and the settlement of the soil after the pile by finite variation of metadata are analyzed, the range of influence of corner effect is obtained. By comparing the difference in ratio of plane strain PSR of two parts on the north side of foundation pit, which explained the building has an impact on the active earth pressure of corner effect.At last, according to the research on the active earth pressure of corner effect of foundation pit, the optimized design of the prestressed anchor cable and the supporting pile in the range of the influence of the pit angle effect is carried out. After the methods of optimization are discussed, the optimization methods of increasing of the lateral spacing of the prestressed anchor cable, reducing a row of anchor cable and change the row spacing and reducing pile diameter are selected. By comparing the three optimization methods, the optimal solution is obtained.In this paper, the pit angle effect of pile anchor support system of deep foundation pit is studied and analyzed, and the optimal design of the pit angle effect is put forward in order to meet the safety of foundation pit support. It not only reduces the cost of the project, but also provides a reference for the study of the pit angle effect in pile-anchor supporting system of deep foundation pit.