Piles used for oil platform foundation in Bohai Gulf, China, are usually over 100m long and 2m in diameter. Such long piles have to be manufactured in segments before installation because of transformation and hoisting difficulties. The segments of the pile are assembled during installation by welding one to another, which often takes one or more days for two pile segments. After pile segment assembling, it proves to be difficult to restart the successive penetration. In this paper the mechanism of pile refusal is discussed and the process of driving a segmented pile is simulated using a finite element program. The calculated results show that when the stick-up stability is satisfied, increasing the length of the last segment of the pile and assembling the pile segments when the pile tip stays in a clay layer can greatly ease the difficulty of restarting pile driving.

1. Introduction

In recent years, more and more oil platforms with six or eight legs have been adopted in Bohai Gulf, China. The leg piles with diameters of 2m or more have to be driven about 100m below the seabed. Due to transportation and hoisting difficulties, these piles have to be manufactured in segments before, and assembled during, installation. Assemblage requires a successive segment to be attached to a formerly penetrated one by welding and often takes one day or more for two segments. During this period of time, the build-up of excess pore pressure in the soil below and around the pile dissipates, to some extent. This increases the strength of the soil and makes restarting the successive penetration very difficult. Even pile refusal may sometimes take place, which is usually very costly and time-consuming. This issue has been encountered quite often in Bohai Gulf and has puzzled the designers there for years.

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