Optimized Selection And Numerical Simulation Of Steel Sheet Pile Support Scheme For Deep Foundation Pit Of Bridge Construction

With the development of bridge construction in China,the scale of bridge foundation pit construction is getting bigger.The statistical analysis of the cases of the foundation pit accident shows that the improperly designed factors accounts for the highest proportion of the accident causes.Therefore,the design of the foundation pit excavation and support scheme is of great significance to the safety of foundation pit.In this paper,based on the background of a deep foundation pit supporting project of a bridge under construction,according to the general situation of the project,engineering geological and hydrological conditions,the steel sheet pile support is determined as the foundation pit supporting scheme.And then two supporting schemes are put forward,which are slope steel sheet pile support and steel sheet pile plus internal support.The design,optimization and numerical simulation of the steel sheet pile support scheme are studied,including:(1)By using FLAC3D finite difference software,the preliminary excavation results of the two supporting schemes for the slope steel sheet pile and steel sheet pile with internal support are simulated,and the horizontal and vertical displacements of the two schemes after completing excavation and support are obtained.The result shows that the horizontal and numerical displacements of the two schemes are within the scope of the specification,which verifies the feasibility of the two schemes.(2)By adopting Analytical Hierarchy Process(AHP),the factors including technical feasibility,operation convenience,safety for use and cost value of foundation pit support are quantified,and the combination of qualitative and quantitative analysis is carried out.Taking the optimal scheme as the target layer,the index evaluation system for selecting better foundation pit support scheme is established.The analysis results show that the weight of steel sheet pile with internal support scheme is higher than that of slope steel sheet pile support scheme.(3)By using FLAC3D finite difference software,the finite element model of foundation pit excavation and support process are established,the numerical simulation analysis of the whole construction process of the optimized scheme of steel sheet pile with internal support is carried out.The deformation of the supporting structure and foundation pit during the construction process is studided.Meanwhile,the monitoring data of the deep foundation pit is compared with the simulation results,which shows that the displacement and deformation of the selected scheme during the construction process are also within the safe range.It proves in a certain degree the rationality and accuracy of the support scheme in the process of execution.Moreover,the deformation and stress of the key parts can be also predicted.In the actual project,reasonable measures can be given in advance to ensure the safe and smooth construction,providing reference for the local or similar bridge deep foundation pit project.