Theoretical Study And In-situ Testing On The Circular Caisson

With the development of pipe jacking and shield project, a singlejacking distance, diameter of pipe jacking and the depth of working wellincreases, and the jacking reaction force acted on caissons is also growing.So open caissons continue to develop to large size or great depth directionwhich makes the interaction between large caisson construction processand the surrounding soil is more complex. This paper made analysis of thefriction in the process of sinking, the mechanical properties of back soil ofcaisson as the working wells of shield or top tube with big top force aftersinking by using3D finite element numerical simulation method and thesite-based experimental study. Main results are shown as follows:(1)The mechanical characteristics of ultra-deep wells in the sinkingprocess were analyzed using finite element analysis software. Focus on themain factors affecting the caisson "sinking factor" such as the lateralfriction or foot blade tip resistance and simultaneously simulate theinteraction between adjacent ultra-deep wells of construction combiningwith the background of the project.(2) The numerical results by field measurement which draw variationof sidewall friction resistance with depth of sinking and discuss the mutualinfluence of ultra-deep wells adjacent to each other were analyzed. Theadjacent walls between two caissons almost have no impact on its sidefriction when using construction synchronous sinking. When there are partitions setting in the adjacent caisson and using open caisson sinkingconstruction program, the side friction of the sinking caisson will increasedue to the influence of squeezing effect of first caisson sinking.(3)The deformation characteristics of back soil of open caisson underthe top force were analyzed by using3D finite element numericalsimulation method, and the main study is the vertical distribution of soilreaction force and horizontal displacement.(4) The numerical simulation results were validated by fieldmeasurement results and make comparative validation of the distributionpatterns of the existing different back soil. The results show that thedistribution pattern of resistance of open caisson is approximated by astraight line which mutates in the depth of the caisson bottom due to thestiffness of the floor at large and reaches the maximum at the foot. Thedisplacement of soil occurs less which makes performance as a wholeunder the jacking force. Simultaneously, we verified the rationality of lessthan the active state in the case that the soil of open caisson produce asmaller displacement under the caisson sinking back below the front wallof the active state is reasonable which gives the variation of sinking backsoil reactions with the different distance.These laws from the study on the sinking process and with top forceof open caisson can provide important reference for guiding future designand the construction of the caisson.