Introduction
Marine and coastal infrastructure are often vulnerable to marine scour and erosion. However, an in-situ concrete mattress can help protect the structural integrity of infrastructures such as ports, bridges and revetments and is often the preferred solution in marine engineering for erosion control.
Fabric-formed concrete uses geotextile formwork to cast concrete, often below the waterline. The formwork is positioned, restrained, and then pumped full of a fluid concrete mix. The filler sleeves are closed, and the concrete is left to cure.
What is a Concrete Mattress?
An in-situ concrete mattress is created when a specially woven geotextile fabric is pump-filled with concrete. The concrete sets and forms a plain, highly durable concrete apron that can range in thickness from as little as 10 cm to as much as 1 metre depending on project requirements.
When concrete is pump-filled into fabric formwork, the water seeps out while sand and cement particles are retained. This process creates a high-strength dense concrete slab than traditional formwork methods, ensuring durable concrete protection over marine infrastructure areas. By this process, it guarantees protection from scour and erosion, extending the lifespan of the structure and, therefore, reducing maintenance costs.
Concrete Mattress Benefits
Adaptability to Seabed Conditions
Conform to a wide range of seabed conditions, whether flat, sloped, or uneven.
This adaptability ensures full contact between the mattress and the seabed.
Efficient Transportation and Installation Process
The installation process of in situ concrete mattresses is straightforward and streamlined.
The lightweight fabric formwork is easy to handle and position, and once installed, it is pump-filled with concrete. As the water bleeds through the porous fabric, a high-strength concrete layer is formed, creating a durable protective apron.
This method reduces installation time, labour requirements, and overall project costs compared to traditional methods.
Reduced Material Usage
Unlike rock armour or precast concrete blocks, in situ mattresses use less concrete
while achieving the same, if not better, level of protection. This efficiency in material usage leads to lower transportation and installation costs and reduces projects’ environmental impact.
Constant Thickness Concrete Mattress
CT Mattress produces slabs of even-thickness plain concrete. The formwork is filled in situ and filled to full thickness on slopes and uneven surfaces.
The formwork is woven 5m wide, and a top and bottom zip joint is used to create shear joints between panels, creating a single slab over large areas.
Constant thickness mattresses can be woven from 100—600 mm thickness, and primary uses are scour protection to:
Open Hole Concrete Mattress
Open hole mattress is a CT Matt with prefabricated holes to provide porosity in wave zones. The hole size and frequency is based upon the locations specific environment, using design references from:
- Yarde & Alsop – 1996
- Hawkswood et al – 2013
The concrete mattress increased porosity protects against a significant 2-3 m wave height. Water is released by the open holes during wave run down, avoiding uplift pressure.
An open-hole mattress can be woven with 100—600 mm thickness, and its primary use is scour protection for revetment slopes.
CT Bulk Concrete Mattress
CT Bulk Mattress is a constant-thickness mattress with large internal ties capable of producing plain slabs up to 1.3m thick. The mattress is made from a double-layer fabric, ensuring robustness, and is bespoke and manufactured for the required concrete height and volumes.
The thickness range is 600 to 1200mm, and common usages are:
- Breaking wave protection to caisson breakwaters
- Protection to wave walls
- Temporary bed protection for tunnelling
Flex Concrete Mattress
Flex mattresses are like CT mattresses but with a grid pattern of reduced thickness. This allows them to flex and cope with soils prone to settlement after mattress installation. The thickness range available is 100mm up to 600mm. The system is helpful for slopes or beds of hydraulic fill that are slow to settle and compact.
Jute Open Hole Concrete Mattress
Open-hole mattresses can be made in jute natural fibre for environmental purposes. The jute fibre decays naturally. The mattress is tailored from strips of jute material. Maximum average thickness is some 200mm and is suitable for wave heights up to 1-1.5m, depending upon the slope angle.
The mattress allows a greater degree of habitat for vegetation and small animals.
Filter Point Concrete Mattress
The double-layer fabric is woven together at regular intervals to join the fabric layers and form filter points, which act as weep holes when the porous mattress is in service. Supplied in panel widths of typically 3 meters.
Learn more about Concrete Mattress
Develop a deeper understanding of why maritime engineers are using this technology in their projects.