Experimental Study On The Applicability Of Split-combined Caisson Foundation In Soft Soil Foundation

The structure of caisson is wellbore,which is to dig the soil in the well,overcome the side friction resistance and blade foot reaction by its own gravity or other methods,then sink to the design level,and then seal the bottom,so that it becomes the foundation of the building,which is one of the important forms of deep foundation.In the coastal areas,the soft soil foundation widely exists,among which there are a large number of silt,silty clay,silt with silt sand,etc.,which has a series of disadvantages and engineering characteristics such as high water content,low shear strength,large pore ratio and low foundation bearing capacity.Traditional large caissons have large bearing capacity and small displacement,but in soft soil areas,subsidence will occur sudden subsidence,well body tilt,piping,soil settlement and other complex conditions.In order to solve these problems,the field monitoring of the subsidence process of large caissons and the subsidence model test of caissons in soft soil foundation with different vacuum preloading degrees were carried out in this paper.On the basis of this,the engineering application of different split combined caissons in soft soil foundation was explored through the model test research of different split combined caissons in soft soil foundation.The main research contents and results are as follows:Firstly,based on the caisson foundation of the Qidu island-tower park section of the Ou river power tunnel project in Wenzhou Lucheng District,the subsidence of caisson in the soft soil foundation was monitored on site.Based on the analysis and calculation of the field monitoring data,the range of the standard value of lateral friction when the caisson is sinking in the local soft soil foundation is obtained.The variation law of lateral wall earth pressure is analyzed and some Suggestions for preventing piping are put forward.The estimation method of blade foot resistance and the influence of sinking of caisson on the settlement of surrounding soil are presented.Second,through the model test to simulate the open caisson in different degree of vacuum preloading treatment of soft soil foundation in the sink,the open caisson pile side friction,wall earth pressure,edge foot resistance,etc,and has carried on the numerical simulation,the results show that with the loss of the moisture content,the open caisson sinking in soft soil of pile side friction increases gradually,when the soft soil moisture content is below 45%,can effectively reduce the soil near the foot blade of open caisson lateral inward,can prevent the open caisson in drop drainage piping phenomenon occurred in the process of.When no mud suction is used in the subsidence of open caisson,the blade footresistance can be calculated by multiplying the blade foot surface resistance by the coefficient of 1.3.When the moisture content of soft soil decreases from 60% to 40%,the influence range of caisson subsidence on the settlement of surrounding soil increases by 25%.The numerical simulation results show that the vertical force on the foot surface of the blade is larger than that on the foot surface of the blade.Finally,in order to reduce the sinking difficulty of large caisson in soft soil foundation and maintain the good horizontal bearing performance of large caisson foundation,a kind of split combined caisson foundation is proposed,which is set separately in sinking period and combined with common bearing capacity in operation period.Based on the model test research of different split combined caissons in soft soil foundation,the change characteristics of displacement-load curve and lateral wall earth pressure are analyzed,and the engineering application of split combined caissons foundation in soft soil foundation is explored.