Tension pile foundation - current design practices and load tests

Abstract

Abstract As the search for oil and natural gas moves into the continental slope, conventional jacket-type steel structures be come economically noncompetitive with the other concepts such as the TLP (Tension Leg Platform) or the Guyed Tower. Although no real data or experience are available at the present time for either TLP or Guyed Tower, many oil companies, including Conoco, believe that the TLP would be the most feasible concept when the water depth exceeds 600 meters. One of the expensive items in the TLP concept is the pile foundation. For instance, Conoco's Hutton TLP will spend 85 million U.S. Dollars or more on the pile foundation template alone. Because of the complicated mechanism of interaction between soil and pile and the lack of field test data and a satisfactory constitutive soil model, simulating the behavior of long piles under cyclic tensile loading current design practice for the tension pile foundation is generally conservative. In order to enhance our knowledge of tension pile foundations, Conoco Inc. has initiated and is sponsoring an offshore, small-scale (7.62 cm diameter) and large-scale (76.2 cm diameter) instrumented tension pile testing research project. The project also includes comprehensive laboratory test programs using a model pile (2.54 cm in diameter) and offshore soil samples. This paper describes the existing technology relevant to the design of tension pile foundations and summarizes the ongoing tension pile testing programs and their objectives. It is hoped that this paper will stimulate high interest for in-situ pile load tests in the Southeast Asia offshore industry so that more tension pile tests will be conducted in the near future. These test data are urgently required in order to save millions of dollars in future TLP pile foundation designs.