Research On Construction Analysis And Key Technologies Of Super-long Steel Sheet Pile Cofferdam Under Deep-water Tidal Conditions

Steel sheet pile cofferdam is a typical flexible supporting structure,which can undergo large deformation under loading.The large deformation of supporting structure,which is located in water,will not affect the surrounding environment.The flexible supporting structure can give full play to the stiffness and strength of its material through its own deformation,which effectively save materials,and has a wide application prospect.Because the construction of deep-water foundation cofferdam is greatly influenced by geology,water flow and depth,the construction difficulty of cofferdam increases sharply caused by the complexity of construction environment,and the construction technology requirements are higher.At present,domestic and foreign research on construction technology of super-long steel sheet pile cofferdam under deep-water tidal conditions is relatively insufficient,and there are few available technical achievements.Taking the construction technology of super-long steel sheet pile cofferdam of a super-large bridge as an example,combined with the specific situation of the site,the steel sheet pile cofferdam is selected as the main pier cofferdam construction scheme of the super-large bridge through comparisons.At the same time,according to the geological survey report,the method of selecting hydrogeological parameters for the construction of 36 m super-long steel sheet pile cofferdam under deep-water tidal conditions is determined.Combined with the finite element software,the stress and deformation of steel sheet pile during construction are simulated,and the finite element calculation model of the whole construction process of steel sheet pile cofferdam is established.The mechanical parameters(deformation and stress of soil layer,steel sheet pile and internal support)of super-long steel sheet pile cofferdam during construction and under deep-water tidal conditions are analyzed with the development of construction steps.The reasonable penetration depth of steel sheet pile is obtained.Based on the research results,a reasonable construction scheme and monitoring scheme are put forward.The main contents and conclusions of this paper are as follows:(1)Considering the hydrogeological conditions,construction and cost requirements of the site,through analysis and comparison,the construction method of super long steel sheet pile cofferdam has the following three advantages.First,the super-long steel sheet pile cofferdam has good applicability,high strength and high waterproof performance.Secondly,the super-long steel sheet pile cofferdam can greatly reduce the economic investment in material cost,and the steel and other resources can be recycled.Third,the super-long steel sheet pile cofferdam can effectively save time and cost.(2)According to the calculation results of 17# cofferdam,the strength and deformation of steel sheet pile and surrounding purlin support,overall stability of surrounding purlin support and anchorage length of steel sheet pile can all meet the requirements.Based on the calculation results,the following suggestions are put forward for the actual construction.When the mud is sucked to-12.5m,the top of the steel sheet pile shall be fixed before the installation of the internal support,and the internal support shall be erected as soon as possible.During the construction process,the deformation and settlement of the steel sheet pile,the purlin and the internal support,the internal and external soil bodies of the steel sheet pile shall be monitored;for the places with large internal support stress,the section steel shall be added stiffening ribs.(3)The finite element three-dimensional space model is established,the interaction between steel sheet pile cofferdam and surrounding soil is fully considered,and the whole process of steel sheet pile cofferdam construction is analyzed.When analyzing the overall plastic strain of soil layer,the maximum displacement in the horizontal direction of soil is less than 56 mm and no continuous circular sliding surface is formed,which meets the requirements of soil deformation and stability.In the simulation of the integral deformation of the internal support,the stress deformation of the I-beam and the circular pipe support are all below 9.8mm,the maximum equivalent stress is 210 MPa.Both of them meet the requirements of deformation and strength of the internal support.Through the comparative analysis of whether there is tide or not,it is concluded that although the tide does bring adverse effects on the construction of the project,the stress and deformation of the steel sheet pile cofferdam structure have some changes,and some indexes have increased obviously,the deformation and mechanical values of the steel sheet pile and cofferdams are within the design range.For the influence of tide,it is necessary to increase the frequency of monitoring during the construction process to ensure the safety of personnel and property.(4)In combination with the stratum and surrounding environment of the site,the layout of monitoring points and the instrument selection are reasonable,monitoring method and observation accuracy meet the requirements of the project and specifications.By the end of construction,the monitoring values of the horizontal displacement of the steel sheet pile top,the horizontal displacement of the pile body and the axial force of the pile body are all in the controllable range,which shows that the support system is stable and reliable.In summary,based on the construction project of super-long steel sheet pile cofferdam of actual super-large bridge,combined with theoretical analysis and measured materials,this article explores and practices the key technologies of super-long steel sheet pile cofferdam construction from construction technology,construction monitoring,construction analyzing and so on,in order to ensure the safe construction of the project.