Pile Driveability Test On Actual Offshore Platform In Calcareous Clay For Qatar NGL Offshore Project
Authors: Tagaya K. , Heerema E.P. , Uchino T. , Kusaka T. 
Published: October 2008

Successful construction of a fixed type offshore platform depends mainly on the proper driving of large diameter piles. This paper reports the summary of useful data obtained in the field measurement of pile driving recently performed for Qatar NGL Offshore Project. Pile driving constitutes a complicated problem to be solved, involving the interaction among the pile, soil and hammer, and even the phenomena of impact. In this test, paying attention to the behavior of a pile, the measurements of driving force, stress in pile, acceleration of pile and displacement of pile were taken. In addition, a wave equation analysis was performed, in which the soil was assumed as Kelvin model. It has been shown that the field-measured values are in relatively good agreement with the calculated values. This report also refers to the considerations to the soil characteristics as well as to the method, results and analysis of the above field measurement.

INTRODUCTION

Recently, the larger sized offshore structures located in deep water have been encountering severe conditions in which large diameter piles had to be driven deeper into the seabed. The successful offshore pile driving is subject to weather conditions and those of the seabed soil which will greatly affect the construction time and cost of the entire project. Therefore, the pile driving analysis has become an extremely important; problem. Particularly, sufficient technology and experience will be required in selection of hammer size, determination of target penetration, prediction of any refusal occurring during pile driving, appropriate countermeasures for such refusal, etc.

The ultimate pile capacity of an offshore platform can be obtained relatively easily by determining the soil characteristics from the results of soil exploration. However, the behavior of a pile being driven represents the combined action of the hammer, pile and soil that may cause a complicated problem. Since Smith 1) proposed in 1960 a method for carrying out the pile driving analysis by solving the one-dimensional wave equation using the difference equation, many studies and accomplishments have been reported. The requirements for carrying out the pile driving analysis include the hammer characteristics and the soil characteristics to be clarified. Therefore, it is the purpose of this paper to clarify the characteristics of calcareous clay by carrying out the measurement of the pile behavior during driving and the wave equation analysis based on the Smith's proposal.

PILE DRIVEABILITY TEST

Location and Offshore Platform:

The Qatar NGL Offshore Project was intended to construct production platforms of liquefied natural gas in the Arabian Gulf approximately 90 Ian off the State of Qatar, as shown in Figs. 1 and 2. This Project included the construction of 13 fixed type platforms built on the pile foundation. Since a great number of piles must be handled on the sea, the successful pile driving operation is one of the keypoints for the success in the entire Project.