Case Histories - Pile Driving In The Gulf Of Mexico

ABSTRACT This paper presents a series of case histories on pile driving in the Gulf of Mexico, demonstrating the value of a pile drivability analysis to the engineer planning an offshore pile driving operation. In this study, actual pile-driving records are compared with the results of pile drivability analyses. Piles in the study varied from 30 to 60 inches in diameter with penetrations to 340 feet. Steam hammers with energy ratings of1rom 60,000 to 300,000 foot-pounds were used. Soils varied from under-consolidated clays with easy driving to dense sands through which driving was very difficult. Also included in the studies is a simplified approach to pile drivability studies in which typical properties for soils, hammers, and cushions are used. In addition, various techniques are used to improve the probability of trouble-free pile-driving. In each case, actual pile-driving records are compared with results of the pile drivability analysis. INTRODUCTION Considerable research has been done in the past concerning the dynamics of pile-driving. Increasing demands of the present day offshore oil industry have necessitated construction of larger platforms in deeper water requiring larger pile with greater penetrations. As this occurs, the driving of the piles becomes more critical to the overall design. Recent attention has been focused on pile driving in new exploration areas such as the North Sea, the Gulf of Alaska, or offshore California. The older, more active producing areas in the Gulf of Mexico have been largely overlooked. One of the aims of this paper is to demonstrate the usefulness and accuracy of pile drivability analyses in the Gulf of Mexico. A pile drivability analysis provides significant benefits during both the designed installation phases. It's 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. 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). Further modifications in the last several years have resulted in more efficient versions of the program (4), but no analytical changes in the program have been made. The version of the program used for this study is the "TIDYWAVE" program (August, 1975) (3).