Nidaplast RA lightweight fill to stabilise the new spillway and protect downstream populations from flooding
To ensure the long-term safety of Toddbrook Reservoir, located in Derbyshire (United Kingdom), 240 m³ of Nidaplast RA600 cellular blocks were installed. This lightweight fill solution was selected by the design engineer ARUP to limit lateral earth pressures on the reinforced concrete walls of the new spillway, while providing outstanding performance in wet and saturated ground conditions.
240 m³
lightweight fill
6
layers of cellular blocks
2025
construction year
Toddbrook Reservoir rehabilitation: context, hydraulic risks and safety challenges
Upgrading a critical structure following extreme weather events
In August 2019, torrential rainfall severely damaged the auxiliary spillway of Toddbrook Reservoir. The incident required the emergency evacuation of 1,500 residents from the town of Whaley Bridge to prevent a major disaster. Investigations revealed that the existing structure, although legally compliant, had deteriorated over time and suffered from design deficiencies.
To permanently secure the site, the Canal & River Trust undertook a major structural reinforcement programme, including the construction of a new 200-metre-long side spillway.
Technical objectives set by the client for reservoir stabilisation (Canal & River Trust)
The technical specifications imposed strict requirements to ensure the stability of the new structure:
Reduce lateral and vertical pressures acting on the concrete spillway walls.
Limit overall structural loads in the immediate vicinity of the dam.
Use a solution fully suited to wet ground conditions, capable of operating in saturated or flood-prone environments.
Ensure fast and safe installation to meet a complex rehabilitation schedule.
Nidaplast RA: lightweight fill solution implemented in a wetland environment
Nidaplast RA600: high-performance lightweight fill for hydraulic applications
The selected solution was Nidaplast RA600, an ultra-lightweight cellular structure made from extruded polypropylene. With a 95% void ratio, this system replaces conventional heavy backfill (approximately 2 tonnes/m³) with a solution weighing only 45 kg/m³. This extreme lightness significantly reduces loads applied to the spillway wall, thereby extending its service life.
Unlike other materials, Nidaplast RA offers a critical advantage for this project: its rigid hexagonal structure allows water to move freely through the fill. As a result, the structure is not subjected to buoyant forces (Archimedes’ principle). In the event of a sudden rise in reservoir water level, the lightweight fill remains stable and in place, with no loss of density or performance.
✅ Major load reduction: extremely low weight limits pressure on sensitive structures.
✅ Water-insensitive material: ideal for frequent wetting and saturation cycles.
✅ High mechanical strength: RA600 provides a long-term allowable compressive strength of 85 kPa (8.5 tonnes/m²).
✅ Eco-responsible solution: 100% recyclable material manufactured in France.
✅ Adaptability: easy on-site cutting to match the complex geometry of the spillway.
Technical characteristics of Nidaplast RA600 lightweight fill
Block dimensions:
2400 x 1200 mm.
Block height:
520 mm.
Bulk density:
45 kg/m³.
Material:
100% recyclable polypropylene
Nidaplast RA
Nidaplast RA lightweight embankments are extremely light and resistant. These honeycomb structures are the recommended solution for constructing landscape embankments, road embankments, or building embankments.
View product sheetLightweight fill installation in wet conditions: construction stages
The installation of 160 cellular blocks was optimised to ensure uniform mechanical behaviour across the entire structure.
1. Preparation
Delivery and inspection of the blocks, followed by installation of a 300 g/m² anti-contamination geotextile.
2. Block installation
Placement of six successive layers with staggered joints to maximise stability.
3. Adjustments
Precise on-site cutting of the blocks to adapt to irregular site conditions.
4. Final works
Final level checks, geotextile coverage and final backfilling.
Watch the video
Results: safety, efficiency and performance of the lightweight fill
The use of Nidaplast RA600 lightweight fill on this large-scale hydraulic engineering project delivers immediate benefits:
Improved safety for downstream populations thanks to a stable and durable structure.
Long-term protection of the spillway wall against lateral overpressures.
Excellent performance in wetland conditions, even during significant reservoir level fluctuations.
Optimised construction schedule thanks to lightweight, manually handled and easy-to-install blocks.
Do you have a development project in a wetland area or on compressible soils? Contact a Nidaplast expert
