Study On Reduction Effect Of Penetration Resistance For Suction Caissons In Sand

Suction bucket foundation is a new type of ocean engineering infrastructure,because of its material costs and installation costs are lower than pile foundation,and is easy to transport and install in costal,thus gradually being offshore wind power industry's favor.Suction bucket foundation sinking process involves the interaction between water-soil and structures,is a more complex,cutting-edge topics.In dense sand,seepage caused by reasonable negative pressure will cause resistance reduction,it is conducive to the completion of the penetration;but seepage damage caused by excessive negative pressure will cause soil failure in the bucket and affect the foundation bearing performance.Existing project showed that the suction prediction in the penetration process is still a corresponding problem.On the basis of existing research,in view of the bucket foundation suction type in dense sand,contrast model test of different wall thickness respectively based on the negative pressure and static pressure were did and two kinds of penetration resistance distribution characteristics were studied,reduction mechanism and reduction effect caused by suction were analyzed.Combined with the experimental results,existing negative pressure prediction method is improved,the main contents and conclusions summarized as follows:1.The development of suction bucket foundation has been reviewed at first of the paper,with which the existing problems and related solutions are identified.It is found that reasonable applying negative pressure is the key to the bucket foundation successfully penetrated in the sand.Based on the problems,the existing research methods and theoretical results are summarized.2.Contrast bucket models of different thickness to diameter ratio were jacked respectively under negative pressure and static pressure.In the process,we had researched the variation law of the pressure between bucket and earth.By contrast,the negative pressure can be very good to reduce the penetration resistance.The final height of soil plug were compared,negative pressure will cause the exceed soil plug which is associated with the model thickness.3.Existing resistance calculation method is evaluated against the result of the model tests.It is found that the calculation results of the static pressure was far less than the measured values.Based on cavity expansion theory,horizontal coefficient calculation method of earth pressure is deduced.By analyzing the soil compaction effect,calculation method of inner earth pressure is put forward.According to the theory of deep foundation bearing capacity,a calculation method of tip stress was proposed.Three methods calculated results was coincident with the measured results.4.Existing critical pressure prediction method is too conservative based on the measured results.Through the numerical simulation,the cloud chart of pore pressure is obtained in the process of penetration.Compared with the measured results,the change rule of the inner soil permeability is found and a new formula is proposed for the critical pressure.