Bridges can suffer from scour when flow conditions change, or when rivers go into flood. This scour can threaten the structural integrity of bridges if allowed to develop, which can lead to settlements and failure.
Fabric formed concrete mattress offers reliable and long-term protection from scour.
Concrete Mattress Solution
Fabric formed concrete mattress seals against the piers and abutments preventing flow from eroding material under the mattress. The slab consists of high-quality plain concrete, able to resist flows of over 6m/s with a design life of 50 years or greater. The slab extends beyond the structure, outside the influence of both local and contraction scour. The edges are usually protected with riprap to prevent underscour occurring or embedded as appropriate.
The mattress fabric is tailored to suit all structures, so that a continuous slab and controlled installation are readily achieved. Fabric formed concrete mattress can be placed in the wet or the dry and is pump filled with micro-concrete. The fabric panels are laid on the bed, zipped together and filled one after another to form the interlocking concrete slab suitable for the shape of the bridge.
The panels can be made large or small to allow construction to proceed quickly, or where required, ensure that a minimum of abutment is exposed at any one time, reducing the risk of settlement during construction.
There are appropriate environmental concerns when placing wet concrete into a watercourse, from increasing turbidity to increasing the alkalinity of the water. In order to obtain the benefits of a cast in place concrete mattress while protecting the environment, it is important to manage these concerns, we do this by:
- Recommending installation in the dry where possible (risk elimination)
- Using good practice installation methods such as tremie filling and careful hose handling (risk mitigation)
- Monitoring pH levels to avoid a pH rise of more than 1.0
Existing bed material can be reinstated over the concrete mattress following installation, minimising the habitat impact while providing high performance scour protection.
Once installed, the continuous concrete slab can resist high flows with little maintenance, while its low thickness maximises both foundation depth levels and flow area capacity combating flooding.