Case Histories: Pile Driving Offshore India

ABSTRACT This paper presents a set of case histories on pile driving for a series of platforms set in the calcareous soils of the Arabian Sea, offshore India. In this study, actual pile driving records were compared with the results of pile drivability analyses performed using techniques similar to those used for piles installed in the Gulf of Mexico. Piles in the study were 48 or 56 inches in diameter with penetrations to 325 feet. Steam hammers with energy ratings of from 60,000 to 540,000 foot-pounds were used. Soils consisted of an alternating sequence of carbonate sands and cohesive calcareous sediments. Also included is a review of a simplified approach to pile drivability studies, in which typical properties for soils, hammers, and cushions are used. These common properties were built into a modified version of the Texas A&M Wave Equation Program, that utilizes only simple descriptions for the pile make-up, hammer, and soil as input. INTRODUCTION A pile drivability analysis provides significant benefits during both the design and installation phases. The primary purpose is to insure proper and efficient pile installation in the field. The analysis accomplishes this by aiding in the selection of proper hammer-cushion combinations, pile wall thicknesses, and add-on lengths for the particular site. The predicted blow counts from the analysis may be quite useful during pile installation in assessing hammer performance and actual soil conditions. This assessment allows the field engineer to determine any changes in equipment necessary during the pile driving operation. Considerable research has been done in the past concerning the dynamics of pile driving. Pile drivability analyses have become quite common in the more highly developed offshore oilfields around the world, such as the Gulf of Mexico and the North Sea. For the under-consolidated clays and sands of the Gu1f of Mexico, and for the over-consolidated clays of the North Sea, the soil parameters for pile drivability analyses have been studied and the results published. For some relatively new areas, such as offshore India, where different soil conditions exist, no data for previous pile driving has been available, and as a result, predicting pile drivability has been very difficult. Without adequate data upon which to base a hindcast, a prediction will be of questionable value. There has been much discussion as to the method and soil parameters to be used for pile drivability analyses offshore India. The purpose of this paper is to present the use of the same simplified technique as used in the Gulf of Mexico, for use offshore India, using the same analytical technique and the exact same soil parameters, allowing the results to speak for themselves. BACKGROUND The method of analysis used for pile drivability analyses is the one-dimensional wave equation, first proposed by Smith (1), and now generally used for dynamic analysis of pile driving. Later improvements were made by Samson, Hirsch, and Lowery (2) resulting in the Texas A&M Wave Equation Program (3).