Subsea Base Collar for Monopile Foundation Stiffness
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Solution Overview
Problem
Monopile foundations for offshore wind turbines face challenges in noise pollution from impact driving, reduced foundation stiffness, and increased embedded length due to hard seabed conditions, which can lead to pile failure and environmental load instability.
Innovation Solution
A monopile foundation design featuring a subsea base with a peripheral collar that increases the diameter of the monopile near the seabed, allowing for vibro-driving and reducing embedded length, while enhancing stiffness and soil dampening, and a method involving a central hub and pile sleeve with grouting and spacers for improved stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If impact driving is used to drive monopile into the sea bed, then the monopile can be driven into position, but noise pollution is generated which is harmful to sea mammals
Solution Approach 1:
The patent replaces impact driving with vibratory driving as the primary installation method. The vibratory driver generates vibrations that loosen the soil around the monopile, allowing it to be driven into the sea bed with reduced noise pollution while still achieving the necessary penetration depth and stability.
Solution Approach 2:
The patent introduces a subsea base with a collar as an intermediary structure between the monopile and the sea bed. This collar distributes the loads over a larger area and provides a transition zone that reduces the need for deep embedding, thereby reducing the duration and intensity of vibratory driving required and consequently reducing noise pollution exposure.
2Object-affected harmful factors
If the embedded length of the monopile is reduced, then noise pollution is reduced, but the foundation stiffness is reduced and control over natural frequency is worsened
Solution Approach 1:
The patent adds a horizontal dimension to the foundation system by introducing a wide collar structure at the subsea base. This collar increases the footprint and moment of inertia of the foundation in the horizontal plane, compensating for the reduced vertical embedding length and maintaining the necessary foundation stiffness and natural frequency control.
Solution Approach 2:
The patent segments the foundation system into distinct components: the monopile, the subsea base, and the collar. This segmentation allows each component to perform its specific function - the monopile provides vertical support, the subsea base distributes loads, and the collar increases horizontal stability - enabling reduced embedded length while maintaining overall foundation performance.
3Ease of manufacture
If impact driving is used to drive monopile into hard rock formations, then the monopile can be installed, but the embedded length must be increased which leads to pile failure risk
Solution Approach 1:
The patent applies local quality by concentrating the driving effort and structural reinforcement at specific locations. The collar is placed at the subsea base level where it provides localized reinforcement and load distribution, allowing the monopile to be driven into hard rock formations without requiring excessive embedded length that would increase failure risk.
Solution Approach 2:
The patent employs preliminary action by using vibratory driving to loosen and prepare the soil and rock formations before final installation. This preliminary vibration treatment reduces the hardness and density of the formation, making it easier to drive the monopile to the required depth with reduced risk of pile failure.
4Strength
If a larger diameter support structure is provided at the subsea base, then the foundation stiffness is increased, but the device complexity is increased
Solution Approach 1:
The patent merges the subsea base and the collar into a single integrated structural unit. This combined structure provides both the load distribution function of the subsea base and the horizontal stability function of the collar, achieving increased foundation stiffness without the complexity of separate, independently installed components.
Solution Approach 2:
The collar structure serves multiple functions: it increases the horizontal footprint for stability, distributes vertical loads over a larger area, provides a transition zone between the monopile and sea bed, and acts as a reinforcement element. This multi-functionality achieves increased foundation stiffness without proportionally increasing device complexity.
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 increases foundation stiffness, reduces noise pollution, allows for shorter monopile lengths, and supports larger turbines, while minimizing soil degradation and the risk of pile refusal, thereby improving the fatigue life and environmental load management of the structure.
Implementation Method 1
increases the amount of soil dampening
Implementation Method 2
vibrating the subsea base into the sea ground so that the collar is at least partially embedded into the sea ground
Implementation Method 3
which can be vibro-driven into the sea bed
Implementation Method 4
an annular space between the pile sleeve and the monopile is grouted
Data Source
Figure 1~3
Figure 4~5
AI summary
The invention refers to a monopile foundation for an offshore tower structure comprising a monopile (3) for receiving the tower structure and a subsea base (1), wherein the monopile (3) is partially embedded in the sea ground (7), wherein the subsea base (1) engages the monopile (3) peripherally and wherein the subsea base (1) comprises a collar (2) surrounding the monopile and being at least partially also embedded in the sea ground (7). The invention also refers to a subsea base (1) for use in such foundation as well as a method for establishing a monopile foundation.