Analysis Of Ultimate Bearing Capacity Of Three Pile Suction Anchors Under Cyclic Loading

Suction anchors are widely used in mooring and anchoring foundations of various floating structures because of their simple construction and convenient recycling.With the continuous progress of offshore oil and gas development to the deep-sea field,the traditional single pile foundation has small uplift bearing capacity,so it needs larger geometric dimensions to be suitable for the new floating structure,which greatly improves the difficulty of transportation and installation and increases the project cost.Three pile suction anchor can effectively improve the overall bearing performance of pile foundation and improve the stability of pile body.Moreover,the geometric size of three pile suction anchor tends to be reasonable,the weight is light,it is convenient for transportation and installation,and the project cost is reduced.Therefore,it is a more appropriate choice.At present,there is little research on the bearing capacity of three pile suction anchor,and there is no systematic basic theoretical framework and calculation formula.Based on this,this thesis makes theoretical and Numerical Research on the bearing capacity of three pile suction anchor,and carries out the following innovative work:(1)Calculation method of cable-stayed bearing capacity of three pile suction anchor.The mechanical performance research model of three pile suction anchor is established,the pile-soil interaction between three pile suction anchor and soil is analyzed,the stress of three pile suction anchor under cable-stayed load is analyzed based on the limit equilibrium method,the force and moment expressions in horizontal and vertical directions are established,and the calculation method of cable-stayed bearing capacity suitable for three pile foundation is proposed.The finite element analysis model under static load is established by PLAXIS software.The sensitivity analysis of parameters such as different length diameter ratio,pile spacing and load angle is carried out,the variation law of ultimate bearing capacity of three pile suction anchor under different working conditions is obtained,and the stability of three pile suction anchor is compared with that of single pile.(2)The influence of shallow gas on the ultimate bearing capacity of three pile suction anchor.The existence of shallow gas will increase the excess pore pressure in the soil layer,so as to reduce the shear strength of the soil layer,which greatly affects the uplift bearing capacity of the suction anchor.According to the existing research results,based on the limit equilibrium method,this thesis numerically studies the uplift bearing capacity of three pile suction anchor in the soil with shallow gas,and compares the uplift bearing capacity of suction anchor without shallow gas with that with shallow gas.(3)The influence of cyclic load on the ultimate bearing capacity of three pile suction anchor.The finite element simulation calculation of the ultimate bearing capacity of three pile suction anchor under static load and cyclic load is carried out,and the calculation results of horizontal,vertical and cable-stayed bearing capacity under the action of the two are compared;The analysis results show that compared with the static load,the cyclic load will significantly reduce the bearing capacity of the three pile suction anchor.