CEL Numerical Investigation On Penetration And Uplift Of Submarine Pipeline In Sandy Seabed

Sandy seabed is widely distributed in the South China Sea.The submarine pipeline directly laid on sandy seabed will penetrating into seabed soil due to hydrodynamic force,dynamic laying and dead loads.The excessive penetration depth of pipelines will lead to large deformation and structural damage of pipelines.Meanwhile,the submarine pipeline is buried in the sandy seabed.High temperature and pressure oil and gas in the pipeline will cause vertical buckling and damage to the pipeline structure.Pipeline structure damage is easy to trigger oil and gas leakage in the pipeline.This will causes enormous economic loss and pollution of the marine environment.Vertical penetration and vertical buckling of pipelines in sandy seabed is a huge deformation process.The deformation degree of pipeline is closely related to the resistance of sand.Therefore,it is of great significance to study the flow mechanism of soil and the evolution of soil resistance during the vertical penetration and buckling of submarine pipelines by using large deformation numerical simulation method for predicting the damage disaster of submarine pipeline structure.The vertical buckling of submarine pipelines is similar to the interaction between pipelines and seabed during the vertical uplift of submarine pipelines.In this paper,the coupled Euler-Lagrange(CEL)large deformation numerical method in ABAQUS is used to set up the numerical model of vertical penetration and uplift of submarine pipeline in sandy seabed.The flow mechanism of seabed sand during the penetration and uplift of submarine pipelines is analyzed.The interaction mechanism between submarine pipelines and soil and the response law of soil resistance are deduced.The influencing factors and law of interaction between submarine pipelines and sand seabed is inferred.The main conclusions are as follows:(1)In the simulation analysis of penetration of submarine pipeline,the displacement-resistance curves of penetration of submarine pipeline under different pipe-soil interface friction coefficients and soil parameters are obtained.The results show that the interface friction coefficient,internal friction Angle and dilatancy Angle of sand soil all affect the bearing capacity coefficient of soil.The pipe-soil interface friction coefficient has the greatest influence on soil bearing capacity coefficients.The bearing capacity of rough surface is 130.86% percent higher than that of smooth surface.According to the simulation results,a formula for calculating the penetration resistance considering the interface friction coefficient of pipe soil,internal friction Angle of sand soil,and dilatancy Angle is proposed.(2)Conduct simulation analysis of updraft of submarine pipelines.The influence of submarine pipeline diameter,internal friction Angle and dilatancy Angle on soil resistance is analyzed under the condition of buried depth ratio H/D=3,H/D=5,H/D=7,H/D=9,H/D=13,H/D=15.The results show that the soil damage caused by pulling up the pipeline can be divided into deep damage and shallow damage.The deep damage only affects the soil around the pipeline,while the shallow damage affects the soil surface.When D=0.3m,the critical depth ratio of deep failure is 9.(3)When the submarine pipeline is pulled up in the sandy seabed,the soil resistance generated by the seabed will increase rapidly to the peak with the increase of the pipeline displacement.The greater the buried depth of the pipeline,the greater the pipeline displacement required to reach the peak resistance,but usually within 0.1D..(4)The pipeline displacement-soil resistance coefficient curves under 54 working conditions were obtained.The effects of friction Angle and dilatancy Angle on the flow characteristics of sand during uplift were analyzed.It provides theoretical support for preventing structural damage of vertical buckling of submarine pipelines.