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In the SUImller of 1989 the Arbroath platform was installed on behalf of Amoco in the UK Sector of the North Sea. A part of the project involved the installation of two docking piles, for locating the platform accurately over the template, and four under-leg piles for giving initial stability to the platform, before the skirt piles had been driven.The paper describes the use of a vibratory hammer, the ICE-14l2, during the installation of the docking and under-leg piles. It describes how the penetration by vibrator was predicted, and how during the initial stage of penetration, control was kept over the verticality of the pile. For the first time the pile inclination was measured continuously during penetration, providing the opportunity to correct the verticality as required. The paper highlights the principles and results of these measurements.The paper concludes that the combination of vibratory hammer and conventional hydraUlic underwater hammer can be very effective for underwater pile installation. The pile verticality can be effectively controlled by continuous measuring of the pile inclination during vibration.

During the summe~of 1987 ICE hydraulic vibratory hammers were used 3 times successfully for subsea installations of anchorpiles and template foundation piles. The hammers proved to be, for the soil conditions encountered, a suitable alternative to conventionally used impact hammers. The present paper will briefly describe the results .of the driveability studies on the basis of which the hammers were accepted and give full details of the three projects. The installations also proved that for the combination of small diameter piles and oyerconsolidated clays, pile plugging may occur. and has to be. taken into account in pile drive-ab~lity calculations. The second part consists of the description of the extension of the stresswave programme TNOWAVE for vibratory hammers and iQ.which case this programme can be of great help to judge the reliability of the vibratory pile driveability studies.

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