Study On Optimal Design Of Pile Anchor Structure System In A Foundation Pit In Beijing

In this paper,based on a foundation pit project in Beijing,finite element analysis method was used to study the influence of different anchor angles,diameters of piles,embedded depths,and the effect of pile spacing on the supporting structure.The orthogonal test was adopted.The method of designing and numerical simulation combines the above several parameters for comprehensive analysis and evaluation to determine the optimal parameter combination of the pile-anchor support structure;finally,the finite element analysis software is used to optimize the supporting structure before and after the support.The main research contents and achievements of the paper are as follows:（1）Three kinds of working conditions are set.In working condition one:the excavation of the foundation pit is completed,and the prestressed anchor bolt applied has not yet functioned;the maximum deformation of the pile is mainly concentrated at the top of the pile;and condition two:the first anchor The bar began to function,the displacement at the top of the pile converged,and the position of the maximum displacement of the pile began to move to the lower part of the pile:Case 3:The deformation of the foundation pit was the largest,and the largest point was mainly concentrated at about 11m,and the shape was approximately"Bow shape.The settlement deformation of the soil around the foundation pit is in the shape of“concave”trough.The maximum position is near the wall 10m away from the pit.The settlement of soil around the external pit of the foundation pit in working condition two to working condition is relatively obvious.Attention should be paid during construction.（2）Analysing the law of displacement changes by various influencing factors shows that the effect of pile diameter,anchor angle,and pile spacing on the displacement of the pile is relatively large,and the influence of embedded depth and prestress is secondary,and the order of the influence factor is:Anchoring depth<prestressing of anchor rod<pile spacing<bolt tilting angle<pile diameter.（3）Under comprehensive consideration of the pit safety reserves,project cost and other factors,according to the orthogonal test results and variance analysis,the optimal combination of parameters is:A₂B₁C₃D₁E₃,the pile diameter is 800mm,and the embedding depth is 3m.The spacing between the piles is 1.7m,and the bolt inclination angle is 10°.Applying 120%prestress to the anchor bolts,the optimized structure can save 11%of the cost.（4）The optimized structure has obvious improvement effect on the deformation of the foundation pit.Among them,the horizontal displacement within 15m of the pile body,the settlement displacement within 30m of the soil around the foundation pit is improved most obviously,but the improvement of the foundation pit uplift is small.