Research On Pseudo-dynamic Method For Deformation Process Of Anchors In Soft Clays

The anchoring foundation in deepwater offshore engineering is exposed to not only the static loads delivered by the up-structures,but also cyclic loads delivered by tension anchors generated by wind,wave,etc.A pseudo-dynamic visco-elastic plastic constitutive model is utilized in research to research into the pseudo-dynamic finite element method to simulate the cyclic displacement accumulation process of anchoring foundation in soft clay under a combined action of static and cyclic loads,involves the following aspects:By utilization of user-defined subroutine of ABAQUS,UMAT,the equivalent linear visco-elastic constitutive model is embedded into the incremental solver of ABAQUS to describe cyclic response of soft clay under undrained condition,and the history of cyclic loads taken into consideration as well.According to the conditions of octahedral shear strain time-histories curve in dynamic response,the octahedral cyclic shear strain of soil can be decided,avoiding the inaccuracy generated by upturning of octahedral shear strain curve.Through describing circulating cumulative response of strain from creep theories,a pseudo-dynamic incremental visco-elastic plastic FE method is proposed to analyze the displacement of anchoring foundation in saturated soft clay under a combined action of static and cyclic loads without detail track of time-histories of cyclic stress and strain.Through Python,calculation of equivalent linearization approximate method to describe the cyclic response of soil and computing of accumulated cyclic shear strain are connected to form a pseudo-dynamic FE method what switches among ABAQUS,PYTHON and MATLAB automatically,and achieves the analysis process by an automatic track of the computer in ABAQUS.Thus repeated manual works and errors are reduced,and efficiency is achieved.The pseudo-dynamic visco-elastic plastic FE method is adopted to simulate the displacement of a tension anchor model in uniform saturated soft clay under a combined action of static and cyclic loads,and compared with the test results.It is indicated that the cyclic displacement calculated inosculates with that measured in model tests,but tendency of the displacement accumulated along the cyclic number is basically the same.Based on the above research,the pseudo-dynamic calculation method is extended to explore the displacement of vertically-loaded anchor in layered saturated soft clay.Through a comparison of the results of FE and model tests,with the increasing of cyclic number,displacement at the mooring point in normal direction of anchor circulating cumulate gradually with a weakening increasing speed,and the tendency of the two methods is similar.This further certifies feasibility of the pseudo-dynamic FE method to simulate the deformation process of deepwater anchoring foundation under a combined action of static and cyclic loads.