Thickness Design Of Cover Concrete For Single Wall Steel Box Cofferdam

With the rapid development of China’s economy,bridge development has entered the golden period,the current domestic deep-water Foundation bridge is becoming more and more common.In the Deep Water Foundation,it is more and more common to build cofferdam to provide construction environment.Cofferdam is a temporary water retaining facility built around the perimeter of the basic plane size during foundation construction in water.The main function of the cover concrete in the cofferdam is to stop the water and resist the float.In the construction of Steel cofferdam,the cover quality of cofferdam directly affects the smooth running of other processes,and the cover concrete is an extremely important part of steel cofferdam.However,it is a difficult problem to determine the thickness of the cover concrete in the cofferdam.The design of the thickness of the cover concrete mainly considers two factors,one is the water pressure strength of the concrete,the strength calculation of the concrete is considered is the water pressure under the bottom of the concrete after pumping the inside of the Cofferdam and the second is a floating body formed by the cover concrete and Cofferdam,whose self-weight should be greater than the buoyancy.In the construction of cofferdam,the concrete pouring area and pouring quantity are large,the construction continuity requirement is high,the large volume crack will appear,so choosing the reasonable thickness of the cover concrete is of great significance to the construction of Coflferdam.The existing research on the thickness design of the cover concrete is mostly about the double-walled steel box cofferdam,and the thickness design of the cover concrete in the Deep water foundation of the single-walled steel box Cofferdam is studied in this paper:based on the reinforcement project of an old Bridge pier,the bridge selects the form of a bottomless rectangular single-walled steel sleeve cofferdam.The whole finite element model of cofferdam with the thickness of 3,3.5,4.4.5,5,5.5 and 6m of the cover concrete is established by ANSYS15.0 respectively,and the most unfavorable conditions of the construction load are applied to the model.By comparing the overall stress and displacement of the cofferdam and the stress and displacement of the cover concrete in 7 groups of models,the optimum thickness of the cover concrete is determined,and the empirical formula of the bottom concrete of the bottomless rectangular single-walled steel box cofferdam is proposed.Through the method of changing the height of cofferdam,it is found that the form of empirical formula is not affected by the height of Cofferdam,which proves the correct form of empirical formula.According to the calculation results of ANSYS15.0,it is shown that the optimum cover concrete thickness of an old bridge is 3.5m,and the empirical formula of the bottomless rectangular single-walled steel box Cofferdam proposed by the author,The empirical formula can provide reference for the determination of the thickness of the bottom cover of a single-walled steel sleeve box cofferdam.