Problems in Design and Installation of Offshore Piles

Offshore structures in water up to 385-ft deep require long pipe piles with ultimate compressive and tension capacities up to 3,500 and 2,000 tons, respectively. Static analysis is the most reliable and widely used method for predetermining pile penetrations and predicting pile capacity. Significant design uncertainties result, however, from dependence on empirical data derived from short, lightly loaded piles driven and tested on land. Pile loads have increased faster than the driving capability of available pile hammers, which include some with rated energy of 180,000 ft-lb. Larger hammers are needed to achieve a higher percentage of successful installations by driving alone. Wave-equation analysis may aid selection of optimum pile wall thickness to improve drivability. Pile installation aids, including jetting, drilling, and grouting, are useful but increase design uncertainty. Four case histories illustrate the problem of both design and installation of offshore piles.