Study On Mechanical Analysis And Time-varying Reliability Of Steel Cofferdam Foundation Pit Construction Under Dynamic Water Load

In recent years,with the continuous development of the construction of municipal bridges in my country,steel cofferdams have become one of the most common forms of support for deep-water foundations due to their good waterproofness,strong stability,and high repetitive rate.However,with the expansion of project scale and the increasing complexity of construction environment,there are more and more adverse factors affecting the structural safety.In order to ensure the safety and stability of the structure during construction,this thesis is based on particle swarm optimization(PSO),support vector machine(SVM),ABAQUS finite element numerical analysis,Kriging interpolation model and time-varying reliability theory.Time-varying reliability assessment is carried out in the whole process of foundation construction.The main research contents were as follows:(1)the influencing factors of water level prediction of small and medium-sized rivers in the city was selected based on the research of the influencing factors of water level at the project bridge site.Through principal component analysis,meteorological data in the medium and short term,the phenomenon of water level top support of main stream,and the supply of nearby adjacent water system were determined as the input influencing factors of PSO-SVM model,and the water level prediction model of small and medium-sized urban rivers was constructed considering meteorological data.It was concluded that the PSOSVM prediction model can be used to predict the water level of small and medium-sized urban rivers in the short and medium term,and meet the accuracy requirements of the actual project duration.(2)Based on the FORTRAN language,the ABAQUS finite element software was redeveloped to realize the real-time change of water level in the construction process,and the finite element numerical simulation was carried out for the actual engineering cases.The influence of parameter uncertainties such as soil parameters,elastic modulus of steel and external water level on deformation and stress of steel cofferdam foundation under water was discussed.It was concluded that the variation of soil parameters has a great influence on the heave of foundation pit,and the variation of steel elastic modulus and external water level has a great influence on the horizontal displacement and support axial force of steel cofferdam.(3)The sensitivity analysis of steel cofferdam underwater foundation was carried out,and the random variables for reliability evaluation were determined.The Latin hypercube was used to sample the random variables and Kriging interpolation model was used to establish the limit state response surface.The reliability evaluation of steel cofferdam underwater foundation was conducted based on the time-varying reliability theory of structure and structural system.It was concluded that the failure probability of the structural system was low before the excavation,and the failure probability of the structural system gradually increased with the excavation process.In this thesis,the time-varying reliability of the structural system during the whole construction process of steel cofferdam underwater foundation is evaluated through a practical project case,which provides a new research idea for the time-varying reliability research of steel cofferdam underwater foundation construction considering the real-time dynamic water load.Steel cofferdam foundation pit construction...