Alternate Foundation Concepts for Offshore Jackets in Calcareous Soils

Calcareous soil type is found at many locations, requiring careful selection of foundation type. Calcareous soil is mostly or partly composed of calcium carbonate in the form of lime or chalk derived from the underlying chalk or limestone rock. North-West Shelf of Australia is an example of site which consists of carbonate soil types wherein the majority of existing offshore facilities and platforms being installed using Drilled and Grouted (D&G) piled foundations and in some instances using Gravity based foundations. This paper discusses alternate foundation concepts on such soils, namely; (i) Micro-piles, and (ii) Inclined pile cluster, along with the common concepts of (iii) D&G piles and (iv) Gravity based foundations. The foundation concepts are discussed with focus on key aspects of the foundation structural configuration, vertical foundation capacity feasibility, and some serviceability related aspects. In addition, offshore operation and installation duration perspective are also discussed to provide some insight on how each foundation concept could suit the project preference which often influence the final selection of foundation concept. Risk/challenges and advantages of each concept are then summarized for overall comparison.