At Ametzondo, Bayonne (Pyrénées-Atlantiques, France), a new commercial development required an access road across entirely waterlogged marshy ground.
The key challenge: prevent ground subsidence while supporting frequent vehicle traffic.
Conventional granular fill on this soft, high water table site would have caused inevitable settlement and structural distress.
The solution: 780 m³ of Nidaplast RA500 cellular lightweight fill — a hydraulically transparent fill that eliminates buoyancy forces and dramatically reduces the load on soft compressible ground.
2015
year of construction
780 m3
lightweight fill
RA500
marshy ground
Ametzondo, Bayonne: Building a Road on Waterlogged Marshy Ground with a Fluctuating Water Table
The Ametzondo zone on the outskirts of Bayonne is naturally marshy ground subject to water table fluctuations. Constructing a load-bearing access road on this type of site presents two interrelated problems: the weight of conventional fill would cause progressive ground consolidation and settlement; and the presence of fluctuating groundwater rules out EPS geofoam, which generates buoyancy forces when submerged and loses its mechanical stability in saturated ground.
Design engineer Egis France and contractor Guintoli selected Nidaplast RA500 as the solution meeting both constraints simultaneously: sufficiently lightweight to limit settlement, and open-cell to eliminate buoyancy forces entirely.
Why Nidaplast RA500 Lightweight Fill Is the Right Solution for Marshy and Wetland Ground
40× lighter than conventional fill — settlement controlled at source
At approximately 40–44 kg/m³, Nidaplast RA500 reduces the load applied to the marshy ground in direct proportion to the depth of substitution.
Where conventional granular fill would exert 1,700–1,900 kg/m³ of vertical stress — causing unacceptable settlement — the cellular lightweight fill transmits only a fraction of that load, compatible with the bearing capacity of soft high water table ground.
Hydraulically Transparent Fill: Zero Buoyancy, No EPS Geofoam Risk
The open-cell hexagonal structure of Nidaplast RA allows water to circulate freely through the fill.
When the water table rises — a frequent occurrence on marshy ground — the fill generates no buoyancy force whatsoever: no uplift, no displacement, no mechanical property loss.
Nidaplast RA is the only lightweight fill qualifying as a hydraulically transparent fill, a property exclusive to open-cell polypropylene honeycomb structures.
This is the decisive advantage over EPS geofoam or any closed-cell lightweight fill alternative in a high water table or flood zone context.
No prior ground treatment required
The cellular lightweight fill is placed directly on the existing marshy ground without prior ground improvement — no stone columns, no soil replacement, no geomembrane.
Blocks are manually handled, which is critical on waterlogged terrain where heavy plant access is limited.
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 on Marshy Ground at Ametzondo: Construction Sequence
1. Block delivery and inspection:
Nidaplast RA500 blocks received and checked on site.
2. Anti-contamination geotextile:
The geotextile separator is placed first, isolating the lightweight fill from the marshy foundation ground and preventing fines migration into the cellular structure.
3. Block installation in successive layers:
Blocks placed with cross-jointed coursing to maximise inter-block stability.
4. On-site cutting:
Blocks cut with a chainsaw to match the road access geometry.
5. Geotextile wrapping:
The geotextile is closed over the top face and lateral faces of the fill mass.
6. Overlying fill and road structure:
Compacted fill and road pavement structure placed above the lightweight fill mass.
Results: A Stable Access Road on Marshy Ground, Open to Regular Vehicle Traffic
- No ground subsidence: load transmitted to the marshy ground reduced to a level compatible with its bearing capacity.
- Hydraulic stability: no buoyancy force, no performance loss when the water table rises or during waterlogging events.
- Frequent vehicle traffic supported: the road structure built above the lightweight fill meets the requirements of a commercial site access road.
- No ground pre-treatment: no stone columns, no soil replacement — cost and programme controlled.
Do you have a road, access or development project on marshy ground, wetland or a high water table site?
Contact a Nidaplast engineer.
Ametzondo zone, Bayonne (Pyrénées-Atlantiques, France): access road construction for a commercial development on naturally marshy, high water table ground. Client: Syndicat mixte d’aménagement de la zone d’Ametzondo. Design engineer: Egis France. Contractor: Guintoli. Volume: 780 m³ of Nidaplast RA500. Date: June 2015.
Solution: Nidaplast RA500 cellular lightweight fill (SAUL — ultra-lightweight cellular structure) in polypropylene (PP), approximately 40–44 kg/m³ dry unit weight, 95% void ratio. Open-cell structure allows free water circulation — hydraulically transparent fill, zero buoyancy force when water table rises. Blocks cut on site to match road geometry. Anti-contamination geotextile wrapping the entire fill mass. No prior soil treatment, no stone columns, no geomembrane.
Outcome: stable access road on marshy compressible ground, supporting frequent vehicle traffic with zero subsidence. Hydraulically transparent fill: no buoyancy force, no performance loss under water table fluctuations. Unlike EPS geofoam, Nidaplast RA500 maintains its dry unit weight and mechanical properties when wet — the only EPS-alternative water-resistant fill validated on a high water table site. 100% French manufacturing. Website: www.nidaplast.com
