Study On Numerical Simulation Of Deep Sea Submarine Pipeline Sinking Process

Submarine pipeline is the oil and gas transportation tool, which connects wells and platform, platform and land transportation facilities. It has the advantages of safety, stability, economy, large conveying capacity and so on. And it is an important part of marine oil and gas transportation system. Laying of the submarine pipeline is divided into bare and buried. No matter which way, submarine pipeline will start sinking due to the action of dead weight after laid. Pipeline will be embedded in seabed, eventually reach the pipe-soil balance. Because the undersea environment and the land environment are different, submarine pipeline is affected by many kinds of load in the process of sinking. So the pipeline is easy to generate large deformation and lose stability, leads to great economic loss and environmental pollution. Therefore, the safety and stability of the submarine pipelines is particularly important.Through finite element software ABAQUS and the application of Mohr-Coulomb constitutive relation, the pipe-soil interaction model in the deep sea is established to simulate the bare and buried submarine pipeline sinking process. Through balancing the soil in-situ stress, setting the pipe-soil contact, applying the weight and buoyancy, analyzing soil consolidation to calculate the vertical displacement of the pipeline and soil. Through a large amount of calculation, we explore the effect of the pipeline and soil related parameters changing on the sinking process. And the calculation results show, for bare pipeline, soil presents settlement trend, and the parameter changes to make the soil more prone to plastic yield, the soil vertical displacement is bigger. For buried pipeline, soil presents uplift trend, when the pipeline is buried shallow and the soil at the top of the pipeline weighs light, parameter changes to make the difference of the pipeline and soil density bigger and soil is more prone to plastic yield, the soil vertical displacement is bigger.At the same time, by setting the birth and death element in the bare pipeline model to make some part of the soil failure, so that it can simulate the suspended span pipeline sinking process and explore the impact of span length on the sinking process. The calculation results show, when the suspended span length is very small, the soil vertical displacement approaches the unsuspended numerical, increases slightly. Once the suspended span length is too large, the two ends of the supporting soil are collapsing, the pipeline will have large deformation and it is very dangerous. Therefore in the pipeline installation and maintenance process, we must take measures to reduce the span length to ensure the safe operation of the pipeline.