The Numerical Simulation Research For The Use Of Prestressed Anchor Flexible Retaining In Deep Foundation Pit Protection

Compared with other retaining forms, the prestressed anchor flexible retaining has already got an extensive application in geo-technical engineering in our country as a new method for the deep foundation pit protection, because of its conspicuous advantage of economy, credibility, convenient construction, deformation small, retaining depth greatly etc.Firstly, this thesis makes an intensive study of the theory about the design and calculation of the prestressed anchor flexible retaining method . then the mechanics function of the prestressed anchor flexible retaining method is simulated and analysed with nonlinear explicit finite difference program. At last this retaining form is researched by changing its structure parameters, and the numerical simulation results is compared and analysed with the monitor on-the-spot in realtime of a factual deep foundation pit project. The main conclusions of this paper are as follows:(1) Based on Bishop supposition, The stability calculating formula of the prestressed anchor flexible retaining is gained. The resolve calculation formula of Bearing capacity of anti-float cable and its critical anchoring length are got by the elastic-plastic model based on partial deformation supposition, and discussing the difference of the critical anchoring length, when the moduluses of grout and rock-soil are changed. The calculation results show that prestressed anchor flexible retaining is more suitable for ductile soil and above.(2) Under the prestressed anchor flexible retaining, The horizontal displacement and vertical displacement of excavation present curvy distributions, the biggest horizontal displacement occurs on the earth surface; the biggest vertical displacement occurs in the pit wall. The distribution of axial force is not homogeneous along the anchor, the axial force is biggest in the face of the fixed part and free part, and it becomes smaller at fixed part. The value of prestress have great effect to the displacement of foundation pit, but when The value of prestress exceedes some value, this effect will become smaller and smaller, and nearly have no change at last.(3) For ductile soil and above , by changing its structure parameters of the prestressed anchor flexible retaining ,the research results show that: it is more economy and reasonable when the fixed length of anchor is between 8 and 20m, the anchor space is between 1.8 and 2.3m, the anchor obiliquity is about 15°, the concrete surface thickness is between 150 and 200mm.(4) Through the calculation and analysis of an engineering case, it proves that the construction of the calculation model is reasonable and it is practical for the use of prestressed anchor flexible retaining in deep foundation pit retaining.