Research On Key Technology Of Large Land Caisson In Deep Silt Overburden

The rapid development of infrastructure construction in my country has resulted in the emergence of large bridges across rivers and seas.The Wufengshan Yangtze River Bridge on the Lianzhen Railway and the Shanghai-Tong Yangtze River Bridge have been built successively.,which have a leading position in technology in the world.The main towers and anchorage foundations of large bridge projects have higher requirements for bearing and stability.The caisson foundation has been widely used due to its high bearing capacity and good economy.The size of open caisson is breaking through,with the increasing span of bridge.There are great differences between super large caisson and small caisson in structural stress and construction control.At present,the design and construction specifications of open caisson are mainly aimed at small water supply and drainage engineering.Many problems such as process control and safety risk have been found in the engineering practice of Nanjing No.4Yangtze River Bridge and Ma'anshan Bridge.In order to solve the technical problems in the construction of super large caisson,the paper carries out soil parameter analysis,theoretical calculation,field load plate test,field model test,etc.And the paper systematically studies the caisson considering the consolidation of sand pile reinforcement,the safety control of the caisson structure,support conversion of caisson,excavation and borrowing equipment of caisson,final settlement technology,construction risk control,etc.The main research results are reflected in:(1)Based on theoretical calculations and field tests,it reveals the distribution of additional stress in large caisson foundations,reveals the consolidation period of 36% high-replacement sand pile composite foundations,and proposes a calculation method of consolidation period considering the overlapping effects of smear areas.And a calculation method for the replacement rate of sand pile composite foundation based on changes in water content is proposed,which solves the problem of temporary foundation treatment of large caisson.(2)Aiming at the problem of safety control of large caisson structures,concept and method of large caisson deflection control are proposed to achieve accurate measurement of relative deformation and quantitative control of structural safety.Through the coordinated deformation analysis and adjustment of caisson deflection,it can quickly realize adjustment of caisson attitude and stress under complex supporting conditions.(3)Theoretical analysis,numerical simulation and indoor experiment are carried out.Through analyzing the stability of sand bag support,a control method for converting semi-rigid sand bag support into flexible sand layer support is proposed.Through adopting multi-node flexible concrete supports,the safety of the structure under the weakly wrapped condition is ensured when the early depth of the caisson is small.Aiming at the problem that the traditional "big pot bottom" excavation method is likely to cause large caisson to crack,numerical simulation analysis is carried out,and the settlement method of multi-point support and reserved core soil is proposed,which solves the problem of safety control of the sinking structure in the construction of large caisson.(4)Aiming at the construction risks of sand gushing and tilting in the final sinking of large caisson in the inclined bearing layer,numerical simulation analysis is carried out,and the method of single-side reinforcement of weak stratum with coordinated settlement and final sinking of small pot bottom of caisson is proposed.(5)The "Four Reamers" high-efficiency soil borrowing equipment is developed to solve the problem of soil borrowing from caisson in high-viscosity formations.(6)Aiming at the construction risk of caisson,based on theoretical analysis,numerical simulation and indoor experiment,the method of correcting the deviation of caisson under weak confinement conditions,the "W-shaped" anti-gushing soil excavation technology,the drag groove reduction and settlement aid technology and sudden subsidence warning methods are proposed.The research and development results have been successfully applied to the construction of the North Anchorage of Wufengshan Caisson and the South Anchorage of Oujiang Beikou Caisson,filling many construction technology gaps of large-scale onshore caisson,and enhancing greatly the influence of China's construction.