Skirted Foundation with Circumferential Openings for Soft Seabed Penetration
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Solution Overview
Problem
Jack-up rigs face challenges in soft seabed conditions where trapped soft material reduces the horizontal bearing capacity and leads to significant settlements due to consolidation under operational loads, and existing methods for removing this material are inefficient or impractical, especially in offshore applications.
Innovation Solution
A skirted foundation design with circumferential openings in the skirt allows soil to flow out as the foundation descends, accompanied by base and skirt tip jetting nozzles to ease penetration, and a membrane for applying pressure to reduce soil resistance, along with internal brackets for stiffening the connection between the skirt and base, facilitating deeper penetration and increased bearing capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a skirted foundation is used to increase embedment depth and horizontal bearing capacity, then the horizontal capacity and bearing capacity are improved, but soft material becomes trapped within the skirt which leads to consolidation settlements and reduced effectiveness
Solution Approach 1:
The skirt is divided into multiple segments with circumferential openings between them, allowing the soft material to be expelled in sections as the foundation penetrates, rather than being trapped in a continuous enclosed space
Solution Approach 2:
The harmful soft material trapped within the skirt is actively removed through the circumferential openings by applying suction or pressure differentials, extracting the problematic material from the foundation interior
2Loss of substance
If suction pumps or eductor systems are used to remove soft material from the caisson interior, then some soft material can be sucked out, but the method is difficult to ensure effective removal when encompassing large area and massive volume of soil
Solution Approach 1:
Instead of attempting to remove massive volumes of soft material through vertical suction from the top, the circumferential openings provide lateral egress paths for the soft material to escape horizontally as the foundation penetrates, dramatically increasing removal capacity
Solution Approach 2:
The circumferential openings are pre-positioned on the skirt to enable continuous expulsion of soft material during the penetration process itself, rather than attempting post-installation removal of already-trapped material
3Loss of substance
If ground preparation work such as excavation is performed to eliminate soft material, then the soft material can be removed, but under-water excavation in soft seabed is often problematic and impractical
Solution Approach 1:
The foundation structure itself serves as the removal mechanism through its circumferential openings, eliminating the need for separate excavation equipment or ground preparation operations in the challenging offshore environment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the bearing capacity of the foundation by efficiently removing soft material and minimizing settlements, eliminating the need for costly or impractical removal methods, and ensuring stable operation under design loads.
Implementation Method 1
If the self weight is insufficient to allow full penetration of the skirt, suction is typically applied within the internal skirt to create under-pressure that results in further penetration of the skirt until reaching the design depth.
Implementation Method 2
base and skirt tip jetting nozzles to ease penetration
Data Source
AI summary
The present invention provides a skirted foundation that can be used in a jack-up rig for providing enhanced bearing capacity. The skirted foundation comprises a spudcan footing having an upper part and a base, wherein the upper part and the base are coupled at their peripherals to form an outer edge, wherein both the upper part and the base have a flat or conical configuration, and wherein the upper part supports one leg of a jack-up rig, and the base has a flat bottom or downward slope, and a skirt having an upper end being integrally coupled to the spudcan footing and downwardly projected to encircle the base and a lower end for penetrating seabed, wherein the skirt comprises a plurality of circumferential openings adjacent to the base of the spudcan footing and located within the top half of the skirt height.