Experimental Study On Floating Stability Of Special-shaped Caisson

As the size of the terminal increases,the main structure(cavitation tank)in the gravity caisson wharf will be super-large,such as the caisson height of the 400,000-ton ore wharf reaching 28 m.Due to the use requirements,the caisson can have an asymmetrical type such as a one-sided toe,also known as a "shaped caisson." The problem of the floating stability of this super-large shaped caisson has become an important issue that must be solved in the construction process.There is no clear provision for the existing specifications for the project.Using the physical model test method,the stability problem when using the hoisting process to float the super large shaped caisson is studied.The experiment considers the effects of floating crane output lifting force,floating speed,wave,water flow,average acceleration of caisson start-up,hanger form and other factors.The variation process of suspension cable lifting force under different test conditions is measured and the caisson attitude is observed simultaneously.The change law of the suspension force of the suspension cable and its relationship with the stability of the caisson are mainly studied.Research indicates:Floating crane output lifting force is the decisive factor for the caisson to maintain the balance of floating.The greater the lifting force of the floating crane,the better the stability of the caisson floating transport,and the more uniform the lifting force distribution of the suspension cable during the floating process.When the floating crane output is insufficient,even in the still water,the shaped caisson can not maintain the balance posture.As long as there is slight interference,the caisson will tilt,the tilt direction is uncertain,and the caisson inclination is mostly spatial and uniaxially inclined.The probability is extremely low and the direction of the caisson tilt depends on the direction of the initial disturbance source.The free liquid of ballast water has an important(adverse)effect on the stability of the caisson floatation.In the case where the caisson is tilted,the ballast water in the caisson will change the position of the center of gravity of the caisson such that the inclination of the caisson gradually increases,and the tilting speed will be faster and faster until the caisson is completely overturned.If the components of the hoisting system have sufficient capacity,the caisson inclination will no longer increase when the caisson,buoyancy and suspension force of the caisson reach a new balance.This process is also a process of redistributing the individual suspension cables.For a caissons(test object)with a length of 19.58 m,a width of 19.21 m(including a front toe of 1.0 m),a height of 28.0 m and a weight of 4575 t,the flow velocity U ≤ 30 cm / s and the wave height ≤ 1 m under the hoisting method using a linear hanger When the wave period is ≤6s and the windless ocean power is used,when the total lifting force output of the floating crane is ≥3200KN,when the caisson moving speed reaches the specified speed(20cm/s)and starts to run smoothly,the single lifting cable can be lifted.Gradually return to a relatively stable state.In other words,when the floating crane output is 3200 KN,it can be regarded as the floating crane output critical lifting force.When the flow velocity U≤30cm/s,wave height ≤1m,wave period≤6s,the influence of water flow and wave on the caisson balance is not significant.The caisson starts from a standstill.Due to the acceleration,the suspension cable will have a short,significant,and non-synchronous increase,which causes the caisson to produce a small tilt.When the floating crane output is insufficient,the caisson will be unstable.During the floating process of the caisson,the floating speed(within the range of 10.9cm/s~150cm/s)also affects the stability of the caisson.The faster the floating speed,the greater the variation of the lifting force of the suspension cable used in the floating caisson.The caisson becomes more stable.However,after the end of the floating,the stability of the caisson will deteriorate as the floating speed increases.Compared with linear hangers,the lifting force of the suspension cable is relatively small when using a rectangular hanger to float the caisson.After the end of the floating,when the caisson reaches a new equilibrium state,the caisson floating by the rectangular hanger is inclined at a smaller angle than that of the linear hanger floating caisson,indicating that the use of the rectangular hanger floats the caisson.The use of a linear hanger floating caisson is more conducive to the uniform distribution of the suspension cable and the stability of the caulking float.It is recommended.