Spatial Effect Analysis Of Convex Corner Of Pile-anchor Support In Foundation Pit Engineering

With the acceleration of China’s modernization process,urban land is becoming more and more tense.It has become an inevitable trend to develop large-scale underground space in combination with urbanization development and planning.Because of the dense buildings inside the city and the complexity of municipal pipelines,various irregular foundation pits appear.Unlike regular foundation pits,irregular foundation pits are complicated in stress and strain due to the existence of various special-shaped corners.The two-dimensional analysis method commonly used at present is not suitable for irregular foundation pits.Therefore,it is necessary to use three-dimensional calculation analysis when designing the support scheme for these irregular foundation pits.Based on a foundation pit project in Lanzhou,this paper carried out a three-dimensional finite element simulation of the entire foundation pit excavation process.Considering the existence of a convex corner in the foundation pit,the foundation pit should not be intercepted according to the principle of symmetry,otherwise the boundary conditions may ultimately affect the simulating results.In order to eliminate the influence of boundary conditions,the foundation pit was not intercepted,but the whole foundation pit was completely simulated.Combined with the three-dimensional finite element simulation results and measured data,the spatial effect of deep foundation pit with a convex corner was studied,and the influence range of corner effect of foundation pit was obtained.On the basis of the actual foundation pit engineering,the influence of the change of the length of the convex corner arm on the deformation of the foundation pit supporting structure is studied.A total of 57 models were expanded.After analyzing the results of a large number of finite element models,The following conclusions are drawn:1.The influence range of the convex corner effect of the foundation pit is about 2 times of the depth of the pit,the influence range of the concave corner effect of the foundation pit is about 1 times of the depth of the pit,and the influence range of the foundation pit excavation on the surface settlement is about 2 times of the depth of the pit.2.According to the difference of the arm’s length of the convex corner,the base pits with the convex corners were systematically classified,and the horizontal displacement patterns of the tops of the piles with convex corners were given.3.The horizontal displacement of the top of the pile at the convex corner is greatly affected by the length of the arm of the convex corner,and decreases with the increase of the length of the arm of the convex corner.When the arm’s length is about 3.5 times of the depth of the pit,the horizontal displacement of the pile at the convex corner tends to be stable.4.Through the analysis of horizontal displacement and vertical displacement at the top of supporting piles,it was found that the horizontal displacement and vertical displacement at the convex corner of foundation pit change rapidly,which indicates that the foundation pit is affected by space effect and the length of convex corner should be paid attention in the design of foundation pit.