Pipelines and sub-sea cables on the seabed are prone to exposure, often due to current erosion of sand and silt bed materials, leading to scour holes forming and unsupported spans. Where monitoring shows the pipe free span is likely to be exceeded, additional support is required.
Custom-engineered grout bags can be used that are pump-filled in situ to provide a solid concrete support. The units can be sized and shaped to provide the appropriate level of support, in combination with additional scour protection in some cases to prevent further underscouring.
Grout bag pipe supports can be readily installed by Divers in depths up to some 50m and by ROV beyond this depth
Where the exposed seabed material is no longer prone to erosion, a simple pipe support block can be used. In most cases, seabed erosion will continue to progress and support blocks with an anti-scour slab base are often used.
Supports must be designed to distribute the pipe load safely onto the seabed without it becoming underscoured. The accelerated flow around exposed pipes threaten underscour erosion. This effect needs to be considered along with general bed erosion or sand wave movement.
Scour protection to pipe supports can commonly be provided by:
- Anti Scour Slab
- Flexible Edge Detail
- Support Embedment
- Rock Dumping
Due to the nature of seabed scour, an appropriate programme of inspection and necessary maintenance is usually advisable.
- Pipe diameter (Ø)
- Underscour/ support height (H)
- Allowance free span
- Submerged pipe weight
- Soil type and ground bearing pressure
- Repair design life
- Estimated future scour potential
- Filled in situ, no heavy lifting / cranes
- Lightweight fabric formwork, positioned by hand then filled in situ by grouting hose
- Fabricated to suit
- Forms concrete to exactly match pipe profile and gap.