Abstract

The paper summarises the results from a study of using skirted foundations as an alternative to piled foundations for two different jackets at two sites offshore Vietnam and Sarawak.

Location A with competent soil conditions was well suited for a jacket design with one “bucket” type of foundation located at each of the four legs. Conceptual structural design indicated a steel weight of less than 60 t for each “bucket” making this alternative cost attractive compared to the conventional piled solution. The total weight saving in steel is estimated to be at least 400 tonnes. The reduction in steel usage and shorter installation time indicate savings of at least US$ 1.7 million.

Location B was not suited for skirted foundations due to the less competent soil conditions. The size of the skirted foundation was so large that, in addition to commercial unattractiveness and technical and operational uncertainties, risks arise for fabrication, jacket loadout, transportation and installation.

The paper presents the design steps for screening the suitability of the skirted foundation concept. Requirements for the field and laboratory investigations programme of the soil at a possible site are discussed.