Pile Installation Performance for Four TLP's in the Gulf of Mexico
Authors: Doyle Earl H. 
Published: October 2008

The installation performance of the pile foundations of four TLP's installed in the Gulf of Mexico is discussed in this paper The TLP's are: Auger, Mars, Ram-Powell and Ursa. Pile diameter's ranged from 72" to 96". All piles were driven to grade with underwater hydraulic hammers.

The self-weight penetration of all piles is compared to that predicted using results of geotechnical investigations. Driving results are shown for the four TLP's and compared with predictions. The effect of driving delays on blow counts is also presented. Three of the TLP's called for the tendons to be directly connected to the piling and were installed without use of guide frames. The final location and tilt of these piles is also discussed.

Introduction

Shell has installed four Tension Leg Platform's (TLP's) in the Gulf of Mexico. The installation of the first TLP began during December, 1993 at the Auger prospect in Garden Banks Block 426. Details are discussed by Ulbricht, et. al., 1994 and Doyle, 1994. The water depth was 2,860 feet. The foundation consisted of four individual templates secured to the sea floor by four 72-inch diameter vertical piles driven to a penetration of 374 feet below the sea floor. Three tendons were attached to each template.

The second TLP was installed at the Mars prospect in Mississippi Canyon Block 807 during April/May, 1996. Details are discussed by Garside, et. al., 1997. The water depth was 2,940 feet. Three 84-inch diameter piles per corner were driven to a penetration of 375 feet. This was the first TLP where the tendons were directly attached to the piles such that the need for sea floor templates was eliminated.

Following the successful installation at Mars, subsequent TLP's (i.e., Ram-Powell and Ursa) used the direct connection methodology to connect the tendons to the piles.

The third TLP was installed at the Ram-Powell prospect in Vioska Knoll Block 956 in May, 1997. Three 84-inch diameter piles per corner were each driven to a penetration of 328 feet. The water depth was 3,214 feet.

The fourth TLP was installed at the Ursa prospect in Mississippi Canyon Block 809. Installation began in November, 1998 and the water depth was 3,800 feet. Four 96-inch diameter piles per corner were each driven to a penetration of 396 feet.

Soil Properties

Either normally or slightly overconsolidated clay underlies each TLP site. Drilling and sampling and in situ testing were conducted from dynamically positioned vessels. The methodologies used are discussed by Dutt, et. al., 1997 and Pelletier, et. al., 1997. For installation considerations, the remolded soil properties are important parameters. The skin resistance for self-weight pile penetration and the resistance to driving are controlled by the remolded soil properties.

The Auger boring was drilled to 490 ft penetration and the results presented elsewhere (Doyle, 1994 and Dutt, et. al., 1992). The undisturbed and remolded soil strengths are shown again in Figures 1 and 2, respectively, along with the interpreted trend lines. The rationale for the interpretation of the undisturbed shear strength at this site and the Mars site was discussed by Doyle, 1994. For Auger, the Miniature Vane (MV) remolded shear strengths were slightly lower than the Unconsolidated-Undrained Triaxial (UU) remolded shear strengths.