Study On Influence Mechanism Of Foundation Excavation Of Deep Silt On Its Enclosure Structure And Adjacent Bridge Piles

With the increasing demand for transportation infrastructure construction in coastal areas of China,due to the complex engineering geological conditions of the site where the foundation pit is being constructed in coastal areas(generally containing deep silt layers),the foundation pit’s own envelope structure and adjacent Deformation control of buildings(structures)is a key problem to be solved urgently in engineering.To clarify the deformation mechanism caused by the excavation of foundation pits under various complex environmental and working conditions is a prerequisite to ensure the safe implementation of foundation pit projects.Therefore,a systematic study is needed.This paper takes the Fujian Mulanxi Super Bridge Project as the research object,and numerically simulates the entire process of 321 # foundation pit construction through the finite element software PLAXIS 2D.The deformation characteristics and excavation of deep pit excavation on deep muddy water are studied.The influence of foundation pit excavation on the retaining structure and adjacent bridge piles is analyzed.The deformation characteristics of the soil surrounding the pit caused by the excavation of the foundation pit under static and variable water level conditions are analyzed.Corresponding optimization and improvement measures are proposed for the most dangerous working conditions and the original design scheme,which can provide a reference for similar projects.The specific research results are as follows:(1)Excavation of deep foundation pits over water under different water level differences,as the water level difference continues to increase,the lateral deformation value of the retaining system composed of steel sheet piles and locking steel pipe piles gradually increases,and the retaining pile The general law of the lateral deformation of the body along the depth direction is a "<" type distribution,and the position of the maximum lateral deformation value of the retaining pile body has an upward trend with the increase of the water level difference;The development trend of the bending moment value in the depth direction is not affected by the water level difference.Under different excavation distances,the lateral deformation value and bending moment value of adjacent bridge piles gradually decrease as the excavation distance increases;when the excavation distance exceeds a certain value,the maximum lateral deformation value of the surrounding pile body,The maximum lateral deformation value of the bridge pile and the maximum bending moment value of the bridge pile will be within a certain range.(2)On the whole,compared with the linear variable water level mode,the simple harmonic variable water level mode has more influence on the lateral deformation of its envelope structure,the lateral deformation of the adjacent piles and the bending moment of the bridge piles.Obviously,the common feature of the deformation characteristics of the retaining structure under the two water level modes is that the maximum lateral deformation occurs after the precipitation in the pit;the linear variable water level mode and the static water level mode cause similar trends in the deformation of the adjacent bridge piles;The maximum lateral deformation range of the soil caused by the excavation of the foundation pit under the conditions of static and variable water levels is concentrated near the excavation surface of the foundation pit.The maximum lateral deformation range of the soil under the variable water level conditions is mainly concentrated in the upper area of the excavation surface.The maximum lateral deformation range of the soil under the condition of static water level is mainly concentrated in the lower area of the excavation surface of the foundation pit.(3)Among the three optimization and improvement measures of adding support,increasing stiffness,and simultaneously adding support and stiffness,increasing support and stiffness at the same time has the most significant effect on reducing lateral deformation of the envelope structure,lateral deformation and bending moment of adjacent bridge piles;In the project,it is recommended to use the optimization and improvement measures of supporting and stiffness at the same time for the simple harmonic water level mode;for the static water level mode,it is recommended to use the optimization and improvement measures for separately applying the support;for the improvement effect of increasing the stiffness separately,the optimization effect Poor,not recommended for use during construction.