1. Abstract:

Pile monitoring was used most recently by SARAWAK SHELL for five offshore platform installations where piles and conductors were installed using steam hammers. This paper describes the experience with pile monitoring, detailing the information obtained during the pile and conductor installation operations and from subsequent back analyses of collected data using stress wave propagation theory. In addition to improved understanding of the hammer behaviour during installation, back-analyses provided a better understanding of the soil behaviour. Also, monitoring and back-analyses were used to confirm pile ultimate static capacities.

2. Introduction

For offshore oil and gas platforms, piles and conductors are typically installed by driving them to the required depth into the founding seabed using hammers. The conductor is the outer-most tubing for conducting oil or gas from the reservoir to surface. "Pile monitoring" is the industry terminology to describe the instrumentation monitoring of the installation operation of both piles and conductors. Sarawak Shell operates as a contractor to PETRONAS, the Malaysian National Petroleum Authority overseeing the national development of the oil and gas resource, under PSCS. Five platforms located some 60 km North-west off the coast of Sarawak state (Figure I), Malaysia, were monitored by others during installation. The steel template platforms designated D18 JT-B, DI8JT-C, BYDP-C and BYDP-D were installed in 1991 whilst the BYR-A was installed in 1992. The soils vary widely between the five locations, the clays are normally consolidated to slightly over consolidated with interlayering of dense to very dense sands at various elevations. Figure 2 describes the pile and conductor make ups and the soil conditions at the respective locations. Despite some 25 years of installation experience in the area, problems are still being encountered, ranging from premature refusals before target penetration depth is reached to unexpectedly low blow counts at target penetration.

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