ABSTRACT:

When tides flow over the ocean floor, they exert dynamic pressure on the porous seabed, and consequently result in oscillatory pore pressure and seepage in the seabed. Stability of the large-diameter pipelines under construction immersed in the seabed may be influenced by the excess pore pressure. In this paper, the authors focus on the tides induced instability of the pipeline in coastal region. The analytical solution in the semi-infinite space is presented and is used to verify the error in the numerical analysis. An engineering case is presented and a finite elementary method approach is taken to solve the problem.

INTRODUCTION

In the latest a few years, a great quantity of undersea infrastructures such as tunnels, pipelines were built in coastal regions, for the necessity of water intake, sewage disposal and so on. Nevertheless, when tides propagate over the seabed, they exert dynamic pressure on the sea floor, which will induce excess pore pressure in the seabed. The shallow buried pipelines with large-diameter are much subject to tides loading during the stage of construction on account of the vast uplifting force. In this paper, the authors gave a practical case to illustrate the affection by tides on the pipe-jacking in the gulf of Xiamen China. For the sake of brevity, we shall simply write the excess pore water pressure as pore pressure in the following sections. Numerous researches had been focused on the ocean wave induced transient response in the seabed and structures. In his study on the wave induced pore pressure around the pipelines, Spierenburg (1986) gave the uplift force on the pipeline based on the potential theory. Furthermore, a physical experiment was set up to model the breakout of the half buried pipe in sand by Foda et.al (1988).

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