Case Histories of Pile Driving in the Gulf of Mexico
Authors: Stockard D.M. 
Published: December 2007

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. Actual pile-driving records are compared with the results of pile-drivability analyses.

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 piles with greater penetrations. As this occurs, the driving of the penetrations. As this occurs, the driving of the piles becomes more critical to the overall design. 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, Gulf of Alaska, and offshore California. The older, more active producing areas in the Gulf of Mexico largely have been overlooked. One of the aims of this paper is to is to demonstrate the usefulness and accuracy of pile-drivability analyses in the Gulf of Mexico. pile-drivability analyses in the Gulf of Mexico. A pile-drivability analysis provides significant benefits during both the design and installation phases. Its primary purpose is to ensure proper and phases. Its primary purpose is to ensure 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 predicted blow counts from the analysis may be quite useful during pile installation in assessing hammer performance and actual soil conditions. This 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, and now generally used for proposed by Smith, and now generally used for dynamic analysis of pile driving. Later improvements were made by Samson et al., resulting in the Texas A and M U. Wave Equation Program. Further modifications in the last several years have resulted in more efficient versions of the program, but no analytical changes have been made in the program. The version of the program used for this study is the TIDYWAVE program (Aug. 1975).

Basic Technique

The model used for the one-dimensional wave equation idealizes the pile system as consisting of a ram, cushion, pile cap, pile, and surrounding soil. The physical and analytical model of a typical pile is shown in Fig. 1. The pile hammer and pile are modeled as a system of concentrated masses connected by springs representing the stiffness of the pile and cushion. The soil is modeled by a spring and dashpot in parallel, attached to each concentrated pile mass below the mudline and at the pile point. pile mass below the mudline and at the pile point. The hammer and cushion properties used in the study are given in Table 1. The values shown are based on those recommended by researchers at Texas A and M U. The factors of hammer efficiency and cushion stiffness have been found to be fairly typical. While the actual hammer used is noted on the driving record, the type of cushion usually is not known.

JPT

P. 580