With the development of deep-sea resource exploration, long steel-pipe piles of large diameter are widely used in offshore platform constructions. Some steel piles may have a diameter that exceeds 2m, and length that exceeds 100m. For such piles, it is almost impossible to accomplish continuous pile driving, as it may be affected by complicated environmental conditions of the sea, the welding of pile connections and the hammer replacement. After a long-term cessation of pile driving, it might become harder to resume and sometimes refusal can even happen. Analyses showed that the soil permeability, the crack development in the soil surrounding the pile, the duration of cessation and the soil-plug effect in the pile pipe are the main factors affecting the soil strength and skin friction. Based on the effective stress principle and the cavity expansion theory, a method has been proposed to evaluate the excess pore water pressure in the soil surrounding the pile during pile driving. In addition, the 1D wave equation has been introduced into the pile-driving analysis. The soil properties in the pile driving analysis are modified in terms of the measured data until the calculated results match the driving records. Therefore, the pile bearing capacity after refusal can be eventually determined.

1. Introduction

Long steel-pipe piles of large diameter have been widely used in offshore engineering. Due to the complexity of working conditions offshore, factors such as weather conditions, ship arrangement and hammer replacement, may prevent piles (deep penetration pile) from being driven to the design elevation continuously, and driving interruptions can take place. In this paper, resuming driving after driving cessation is called re-driving. It can take hours, days or even a few weeks to restart the pile-driving process. Long-term cessation can lead to excess pore water dissipation and soil strength setup.

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