Study On Seabed-Pipeline Interaction Under Random Wave Loading

As one kind of engineering structures, pipeline (placed on the surface of seabed or buried in the seabed) is widely used to transport petroleum and natural gas. In the design of submarine pipeline, among all the loadings the wave loading is predominant. In the propagating process of gravitational waves over the ocean surface, the periodic fluctuating pressure is generated upon the seabed. With the pressure propagating into the seabed, they cause pore pressure and additional effective stress, and then the effective stress of seabed will be changed. On the other hand, the existing pipeline influences the distribution of stresses around the pipeline, which possibly causes soil liquefaction and destruction of pipeline. Instability of pipeline causes the leakage of gas and oil, which results in financial loss and huge environmental pollution. Therefore, for reasonably evaluating the stability and safety of submarine pipeline under wave loading, we must consider the wave-induced dynamic response of seabed and pipeline exactly. But on account of the complexity of the soil characteristics, the shape of pipeline and the form of wave, this engineering problem have not been solved drastically, so far, the design of pipeline is restricted to experimental verdict. So with the developing of offshore oil field and expanding of engineering scale, to evaluate the safety and stability of pipeline exactly is of essential importance.Today most investigations are only concentrated on discussing the dynamic response of the buried pipeline under linear regular wave without considering the stochastic behavior. Based on generalized Biot’s dynamic consolidation theory and random wave theory, a2-D FEM model for simulating seabed-pipeline interaction is established with considering the contact between the pile and soil and inertial effect. Based on the numerical results we found that the excess pore pressure and vertical effective stress along seabed depth are significantly different, and also the internal stress of pipeline and excess pore pressure around the external surface of pipeline under random and representative waves. Numerical results further indicate that the stochastic behavior of wave loading have a significant impact on the dynamic response of pipeline, the dynamic response of pipeline will be underestimated once we ignore it. So the stochastic feature of random wave has to be duly taken into account in the design and safety evaluation of submarine pipeline.For the contact and inertia effects respectively, the difference of dynamic response of the buried pipeline is discussed in detail. Numerical results demonstrate that the contact effect plays an important role in the estimation of the internal normal stresses, but not the excess pore pressure, while the inertia terms will affect the results to a small extent. Based on the above analysis, the influence of buried depth and radius of pipeline on the difference value obtained from considering or ignoring the contact and inertia effects is also discussed. The results indicate that the buried depth and radius of pipeline will affect the difference value remarkably. With adopting parametric analysis method, we emphasize on studying the influence of different permeability coefficient, deformation modulus and degree of saturation on vertical displacement of pipeline and the excess pore pressure and vertical effective stress along depth near the pipeline. The influence of buried depth and radius on the vertical displacement and internal normal stresses under different permeability coefficients, deformation modulus and degrees of saturation is studied in detail with considering the contact and inertia effects together.