Research On The Axial Pipe-Soil Interaction Based On The Combined LDFE And SSFE Methods

The safe and reliable operation of submarine pipelines is the fundamental guarantee for the production and transportation of offshore oil and gas.During the operation of the submarine pipeline,it needs to withstand high temperature and highpressure working environment and harsh wave current environment load,and its on-bottom stability under cyclic loads is particularly important.The seabed soil is the only source of resistance during the service period of the subsea pipeline.Therefore,identifying,understanding and quantifying the deep-sea pipeline-soil interaction is an indispensable link in the subsea pipeline design.This research focuses on the axial stability of deep-sea pipelines.Starting from the latitude of the pipe-soil interaction unit,with the help of the high-efficiency calculation of the large deformation finite element of the pipe-soil interaction unit,it simulates the evolution of the soil shape and strength around the subsea pipeline during the laying process.The stress and strain state of the soil around the submarine pipeline are mapped to the three-dimensional small deformation finite element model,and the subsequent in-situ axial stability analysis is carried out as the initial state,which realizes the efficient simulation of the entire process of subsea pipeline installation and in-position.First of all,in view of the pipeline laying problem,the large deformation finite element analysis method was used to simulate the penetration of the submarine pipeline,and the properties of the pipe-soil interface were fully considered.The comparison and analysis with the published centrifuge test and numerical simulation data verified the great effect of the finite element model.Based on the verification model,the research focuses on the remodeling mechanism of seabed shape and seabed soil strength when the pipeline is embedded in different seabed depths,and quantifies the influence of soil berms on the effective contact area of the pipe-soil.Subsequently,in view of the influence of the pipeline laying process on its subsequent in-situ axial stability,based on the large deformation results of pipeline laying,a three-dimensional finite element pipe-soil effect unit model of submarine pipeline axial movement was constructed by using free boundary surface tracking and field variable interpolation mapping methods,.The research focuses on the influence mechanism of the seabed reshaping shape on the axial resistance,and by considering the strain rate enhancement and strain softening factors during the pipeline laying process,an in-depth analysis of the excitation mechanism of the axial friction resistance per unit pipeline is carried out.In addition,in view of the axial pipe running of the pipeline,through the threedimensional finite element pipe-soil effect unit model of submarine pipeline axial movement of embedded pipes and laid pipes,the control factors of axial pipe-soil action such as axial shear velocity and cumulative plastic strain are considered,and the unit is quantified by correlation characteristics of pipe axial friction and typical mechanical indexes of seabed soil(soil sensitivity,soil ductility factor,strain rate factor).Based on the above research,this paper deeply reveals the influence mechanism of seabed clay strain rate and strain softening characteristics on the axial action of pipe soil.Using the combined large and small deformation technology,the development mechanism of unit pipe axial friction resistance is successfully quantified,which is a solution to marine engineering.A large-scale design problem in the field "The influence of the installation process on the axial stability of the subsea pipeline" provides a new idea.