Optimized Design Of Support Scheme For Excavation Of Foundation Pit Adjacent To Built Piers

With the increasing urbanization process in China,the shortage of construction land has gradually expanded,and it has gradually expanded into high-rise buildings and underground space.The development of underground space is generally directly related to foundation pit construction,and foundation pit construction will inevitably affect the surrounding building complex and underground facilities.In order to control this effect within a safe range,it is particularly important to select a more suitable foundation pit support scheme.Based on a box culvert foundation pit project located in Shabei New District,Jingzhou City,this paper optimizes the foundation pit support scheme of adjacent viaduct piers.By establishing a comprehensive fuzzy evaluation system for building safety,the preliminary support scheme was comprehensively selected and the preliminary optimal scheme was determined.Based on the selected preferred scheme,the soil settlement,supporting structure deformation,and deformation and displacement of adjacent bridge piles caused by foundation pit excavation were analyzed by using the software and finite element numerical simulation scheme of Lizheng deep foundation pit.Finally,the parametric analysis of the supporting structure is carried out,and the foundation pit support scheme is optimized,which further reduces the impact of excavation on adjacent bridge piles,enhances the stability of foundation pit and bridge structure,and can provide reference for subsequent related projects.In this paper,the following studies are mainly carried out:(1)Foundation pit support scheme is preferred.According to the excavation depth of the foundation pit,the soil parameters given by the project and the characteristics of the surrounding environment,several suitable foundation pit support schemes are preliminarily selected.The design and calculation of the supporting structure of the underground continuous wall,pile anchor and SMW construction method were carried out by using the relevant specifications and the software of Lizheng Deep Foundation Pit,and the multi-objective decision-making model was established with safety,economy,environmental protection,construction difficulty,and deformation control ability as the main goals,and the support scheme with a variety of alternative support schemes was compared and the preferred scheme was determined.(2)Construction impact analysis of preferred support scheme.Based on the excavation process of foundation pit under pile anchor support,a three-dimensional finite element numerical model was established,and the deformation of the envelope structure,the deformation law of surface settlement and the influence of foundation pit excavation on adjacent bridge piles during the excavation process of foundation pit were analyzed.The surrounding surface settlement is "spoonful",but there is a slight mutation in the position of the bridge pile;The uplift deformation of the bottom of the pit shows a tendency to be large in the middle and small on both sides;The horizontal deformation and bending moment of adjacent bridge piles were mainly distributed in the upper part of the pile body and increased with the deepening of excavation of the foundation pit.Uneven settlement will occur between the piles of each bridge,and the horizontal deformation,vertical settlement and uplift,and bending moment of the pile body caused by the excavation of the foundation pit are not beyond the specified monitoring range.(3)Comparison between the optimization scheme and the original scheme.Through the software analysis of the design calculation software and finite element software simulation of the deep foundation pit,the horizontal deformation of the supporting structure,the settlement of the surrounding surface soil,and the horizontal displacement of the bridge pile were compared and analyzed during the excavation of the foundation pit under the original support scheme,namely the cement soil wall,and the preferred support scheme,that is,the pile anchor support.The analysis results show that due to the improvement of the stiffness of the soil near the foundation pit by the cement-soil mixing pile and the large thickness of the wall,the settlement of the surface soil around the foundation pit under its support is less than that under the support of the pile anchor.However,when excavating the foundation pit under the support of pile anchor,the horizontal deformation of the supporting structure and the adjacent bridge pile is smaller than that of the cement soil wall,which further indicates that the influence of the preferred scheme on the excavation of the foundation pit has a certain improvement effect,which confirms the rationality and effectiveness of the preferred scheme.(4)Parametric analysis of optimal support scheme.On the basis of the preliminary optimal support scheme,parametric analysis is carried out.The influence of excavation of foundation pit on horizontal deformation and vertical settlement of adjacent bridge piles under different pile diameters,pile net spacing and pile embedding depths was studied,and the supporting scheme of foundation pit was finally optimized through analysis.The results show that the diameter of the supporting pile is negatively correlated with the deformation of the bridge pile,the net spacing of the pile is positively correlated with the deformation of the bridge pile,and the embedding depth has little effect on the deformation of the bridge pile.Compared with the preliminary selection scheme,the control effect of the deformation of the bridge pile is significantly improved and the cost is not much improved,which indicates the effectiveness of parameter optimization of the support scheme.