ABSTRACT

Standing wave-induced interaction of seabed-pipeline in the elasto-plastic saturated sandy seabed has seldom been investigated. By combining standing waves, the Biot's consolidation theory and the sand constitutive model for post-liquefaction behavior by Zhang's research group, an elasto-plastic method was proposed. This method is capable of simulating oscillatory and residual pore pressures simultaneously, which was first validated by wave tank experiment. Then, three types of numerical models with different pipeline positions using this method were conducted, through which, the developing process of soil liquefaction around the pipeline and differences of dynamic responses in the three models were investigated.

INTRODUCTION

Flotation of buried pipeline caused by the occurrence of soil liquefaction under severe wave motions has been reported and investigated by Christian et al. (1974), Damgaard et al. (2006) and etc., which is one of the main threat to the stability of pipeline.

In literature, many research on the interaction of pipeline and sandy seabed under wave loadings has been performed only considering the influence of upward seepage forces (MacPherson, 1978). However, the sandy seabed is an elasto-plastic material under relatively large wave motions in realistic ocean environment. Few elasto-plastic constitutive models, like the PZIII (Pastor et al., 1990) constitutive model, have been adopted in the analysis of wave-induced soil liquefaction, and even in the interaction of pipeline and seabed under dynamic loadings (Dunn et al., 2006). Ye and Wang (2016) figured out that PZIII constitutive model is capable of describing the post-liquefaction behavior of loose seabed soil to some extent. Zhang and Wang (2012) proposed a theoretical framework for post-liquefaction deformation of loose, medium or dense saturated sand under cyclic loadings based on the underlying mechanics of sand liquefaction, which has been adopted in analyzing the process of soil liquefaction around pipeline under progressive waves (Wang and Zhang, 2018).

In ocean environment, when a progressive wave encounters with a vertical and rigid wall of marine structures, a reflected wave could be generated in the opposite direction, the superposition of these two waves may result in a standing wave, which is considered more common around marine installations compared with progressive waves. Dynamic responses of seabed induced by standing waves have been studied by many researchers (Jeng, 2012). However, the standing wave induced interaction of seabed-pipeline, which might occur when the pipeline is close to gravity marine structures, has seldom been investigated.

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