Research On Key Technology Of Deepwater Construction Of Single-wall Steel Cofferdam

Steel cofferdam is a common pile foundation construction method in deep water areas.However,the underwater construction environment in deep water areas is complex and changeable,and it is easy to disturb the structure of steel cofferdam,which is one of the main factors that cause engineering safety accidents.At present,the construction of steel cofferdam relies more on the relevant experience of technical personnel due to factors such as many underwater disturbances,poor operating conditions,and complex processes,resulting in uneven construction levels.Therefore,it is of great engineering significance to study the structural mechanical properties of the steel cofferdam during construction and carry out targeted optimization design,study the appropriate thickness of the bottom sealing concrete,and propose a reasonable lowering device and method to improve the construction quality and safety of the cofferdam.This paper takes the single-wall steel cofferdam as the research object,and carries out researches on the optimal design of the steel cofferdam structure,the analysis of the thickness of the bottom sealing concrete,and the deviation prevention lowering device.The main research contents and conclusions are as follows:(1)Based on engineering hydrological conditions and cofferdam structure parameters,a spatial finite element analysis model of single-wall steel cofferdam is established.By analyzing the stress condition of the steel cofferdam under the most unfavorable working conditions,the combined stress analysis of the steel cofferdam is carried out according to the load combination method in the "bridge specification",and the comparative analysis is carried out with the design requirements of the specification.Based on the calculation results,the weak parts of the steel cofferdam structure are analyzed and determined,and a plan for local reinforcement is proposed to ensure the safety of the steel cofferdam construction process.(2)On the basis of verifying that the safety of the single-wall steel cofferdam structure meets the requirements of the specification,in the thickness interval of 1.5-3.3m,MIDAS FEA NX analysis software is used to establish 7 groups of bottom sealing concrete refinement model with a thickness interval of 0.3m.By comparing and analyzing the stress and displacement data of bottom sealing concrete with different thicknesses,the optimal bottom sealing concrete thickness under specific working conditions is determined.And based on the numerical simulation results,the nonlinear fitting function is used to fit the thickness-displacement formula of the bottom sealing concrete of the steel cofferdam,which provides a reference for the structural design and engineering construction of the related steel cofferdam.(3)On the premise that the structural safety and stability of single wall steel cofferdam meet the specification requirements,a set of lowering auxiliary device for deviation prevention of steel cofferdam with early warning is proposed by analyzing the problems of easy deviation,difficult control and no early warning in the process of steel cofferdam lowering construction.The device controls the horizontal and vertical displacement of the underwater steel cofferdam by means of telescopic gears,and provides real-time data transmission and early warning prompts through sensors and early warning devices to ensure the construction safety of the steel cofferdam and improve its lowering accuracy.At the same time,according to the prevent deviation lowering auxiliary device of designed steel cofferdam,a new steel cofferdam lowering construction method is proposed to guide the on-site construction of steel cofferdam.(4)Taking the construction of an underwater single-wall steel cofferdam of a new bridge as an example,the construction process from the processing of the steel cofferdam to the successful sealing bottom is analyzed in detail.Combined with onsite monitoring and finite element model for comparative analysis,the rationality and safety of the single-wall steel cofferdam structure and the thickness of the bottom sealing concrete are verified.At the same time,according to the engineering problems encountered during the construction of the steel cofferdam,based on the analysis and demonstration of the finite element model,a targeted solution is proposed to provide technical reference for similar engineering construction.