When a jackup deploys at a location and then moves away, it leaves footprints which can affect subsequent jackup deployment at the same location. This paper explores the literature of footprint interaction in soft clay, and discusses a number of foundation solution concepts which show promise in enabling a jackup to be positioned with tight positional tolerances at any desired location, irrespective of pre-existing footprints. Techniques for further investigations are briefly reviewed.
When a jackup deploys at a clay location and then leaves, it can create footprints that can be several meters deep (Jardine et al, 2001). If the clay is sufficiently soft, the spudcan may have actually penetrated much deeper than the observed footprint. When the penetrated spudcan is pulled out, much of the soft remolded clay will flow around it and back into the hole, leaving a deep region of disturbed soil (Stewart and Finnie, 2001). The disturbed soil can have a lower strength than the intact material around it, and a lower stiffness. The footprints, and the associated remolded soil, can potentially present significant hazards for subsequent jackup deployments at the same location, including:
Loss of positional and heading control during installation, with some similarities to punchthrough, leading to structural damage to jackup or platform, and delayed or abandoned installation,
Excessive eccentricity of footing reaction, during installation or in subsequent service, potentially leading to significant rack phase difference, with leg and/or bracing damage or failure,
Absence of symmetry in footing load-displacement and moment rotation yield and strength responses in subsequent operational and storm loading, and potentially changes to dynamic response.
The objective of this paper is to document a preliminary review, primarily theoretical, focusing on geotechnical aspects.