Grooved Polymeric Subsea Foundations for Directional Sliding
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Solution Overview
Problem
Conventional subsea foundations face challenges in supporting heavy structures on soft seabed soils, resisting thermal expansion, and maintaining stability against lateral loads, while existing solutions like mudmats and grillages have limitations in size, cost, and friction issues that lead to unintended displacement.
Innovation Solution
A sliding subsea foundation with a polymeric shoe layer featuring elongate grooves, made of high-density polyethylene (HDPE), which reduces friction in the longitudinal direction to allow for thermal expansion while maintaining stability against lateral loads by adjusting the interface friction angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional mudmat foundation is used to support heavy subsea structures, then the structure can be supported on soft seabed soils, but the foundation experiences high friction with the seabed that causes unintended displacement and prevents accommodation of thermal expansion
Solution Approach 1:
The foundation incorporates a porous or perforated base structure that allows seabed soil to pass through, reducing the friction interface between the foundation and seabed. This enables the foundation to slide more freely to accommodate thermal expansion of pipelines while maintaining load-bearing capacity through the distributed soil contact throughout the porous structure.
Solution Approach 2:
The foundation uses different materials for different functions: a porous base structure for minimizing friction and enabling movement, combined with a non-porous top plate for providing stable support and distributing loads. This local differentiation allows simultaneous achievement of movement capability and load-bearing strength.
2Adaptability or versatility
If the foundation is designed to allow horizontal movement to accommodate thermal expansion, then the pipeline is less prone to buckling, but the structure becomes vulnerable to excessive lateral displacement under lateral loads
Solution Approach 1:
The foundation employs directionally differentiated friction characteristics through the porous structure orientation and topology, creating lower friction resistance in the longitudinal direction to accommodate thermal expansion while maintaining higher friction resistance in lateral directions to prevent excessive lateral displacement under lateral loads.
Solution Approach 2:
The foundation design allows dynamic adjustment of friction characteristics based on load direction and magnitude, enabling free movement during thermal expansion while providing stability resistance during lateral loading events, effectively making the friction property adaptive rather than static.
3Stress or pressure
If a large mudmat is used to spread weight loads and avoid embedment, then the bearing area is sufficient, but the cost, weight, and installation complexity increase significantly
Solution Approach 1:
The porous or perforated base structure allows seabed soil to pass through and contact the foundation at multiple points, effectively distributing the weight load across a larger effective bearing area without requiring a large surface footprint. This reduces the physical dimensions and weight of the foundation while maintaining adequate pressure distribution capabilities.
Solution Approach 2:
The foundation base is segmented into multiple openings or pores that allow independent contact points with the seabed, distributing the load across numerous small contact areas rather than requiring a single large continuous base, thereby reducing overall foundation size while maintaining load-bearing performance.
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 enables cost savings, reduced installation time, and minimized displacement of subsea structures by optimizing the friction interface between the seabed and the foundation, allowing for efficient thermal expansion and resisting lateral loads.
Implementation Method 1
the friction angle at an interface between the foundation and the seabed soil may advantageously be lower in a longitudinal direction parallel to the length of the or each groove than in a transverse direction orthogonal to the length of the or each groove
Implementation Method 2
engaging soil of the seabed with a soil-engaging face of the shoe layer, which face comprises at least one elongate groove
Data Source
AI summary
A sliding subsea foundation comprises a polymeric shoe layer on the underside of a mudmat or subsea structure. The shoe layer defines a soil-engaging face that comprises an array of parallel grooves. The grooves are shallower than the thickness of the shoe layer such that each groove has a closed top, defined by and integral with the shoe layer, that spans the groove. Where a subsea structure is supported on the foundation with a subsea pipeline attached to the structure, the grooves are substantially parallel to a longitudinal axis of the pipeline.