Project and Environment
The Nouvelle Route du Littoral (NRL) is one of Europe’s most ambitious marine road projects. Located on the French island of La Réunion in the Indian Ocean, the project aims to replace the cliff-hugging National Route 1 with a safer and more resilient alignment extending over the sea. Subject to tropical cyclones, heavy wave action, and seismic risk, the island’s coastal infrastructure has long been vulnerable to closure and damage. The new route includes 5.4 km of elevated bridge constructed offshore between 80 m and 300 m from the shoreline.
This viaduct section comprises precast concrete deck segments supported by 48 marine piers, each founded on rock strata at seabed level. Due to the need for precise alignment of the deck, the foundations of each pier had to meet extremely tight positional tolerances and deliver immediate full-area bearing contact, without settlement or post-installation adjustment.
Given these constraints, Proserve was commissioned to provide an engineered in situ concrete foundation solution using its grouted fabric formwork system, pre-attached to the underside of each pier base.
Foundation System Selection and Design Objectives
The design team required a foundation interface that would:
- Ensure intimate contact between the precast pier base and the underlying gravel bed or rock outcrop
- Accommodate irregularities in seabed elevation, without additional underwater concrete levelling
- Eliminate long-term settlement to maintain precise pier head height and alignment across the viaduct
- Enable fully surface-controlled installation and grouting to avoid diver activity in high-flow marine conditions
- Provide structural durability in a zone subject to wave impact, current scour, and potential seismic acceleration
The selected solution was Proserve’s grouted fabric formwork system, engineered to deliver a tailor-formed concrete base in situ through remote-controlled grouting operations, following successful precedent in projects such as the MOSE flood barrier in Venice and the Second Severn Crossing.
System Configuration and Fabrication
Each pier base—either 20 m or 23 m in diameter—was cast in a controlled yard environment. Six independent grout bag compartments were attached beneath each unit during fabrication using factory-manufactured, grout-tight but water-permeable woven fabric.
Each compartment was:
- Condensed and folded for transport beneath the pier using break ties and protective sheathing
- Connected to dedicated cast-in filler sleeves running through the pier shaft to deck level
- Fitted with vent sleeves at the perimeter, equipped with grout sensors for pressure monitoring and fill confirmation
The formwork was sized to allow for differential seabed conditions of up to 900 mm variation, meaning the contractor did not need to lay fine-grained stone, other than enabling a moulded concrete interface.
Installation Process and Offshore Execution
The piers were transported offshore and positioned using a gantry crane operating on the temporary construction trestle. Each unit was landed onto a pre-prepared working layer of gravel placed on rock outcrop. Four external jack legs provided temporary vertical and lateral stability until grouting was completed.
Grouting was conducted via the prefixed filler sleeves using a high-flow sand:cement micro-concrete mix, produced at the onboard batching plant and tremie-pumped to the base compartments. Each grouting operation typically lasted between 12 and 16 hours, with bag inflation monitored continuously via the surface control panel linked to the vent sensor array.
The grouting sequence was designed to:
- Begin with central compartments to ensure axial seating
- Progress outward radially to minimise potential lift or rotation
- Halt automatically once full contact pressure was detected at each vent
This highly controlled sequence allowed for compensation of both macro (bed undulation) and micro (gravel layer thickness) tolerance within the foundation footprint.
Engineering Performance and Outcomes
Proserve’s foundation system enabled consistent and repeatable foundation construction across all 48 pier locations, despite highly variable sea conditions and difficult site access. The grouted formwork solution delivered:
- A cumulative foundation area of over 17,000 m²
- Approximate grout volume of 3,500 m³, placed entirely from the surface
- Fully monitored compartmental filling for every pier
- Load-bearing interfaces free from voids, washout, or settlement potential
The system eliminated the need for large-volume underwater concrete pours or diver-placed levelling operations, significantly reducing risk in the offshore work zone. It also provided long-term stability, contributing to the accuracy of bridge deck alignment and the durability of the structure in a high-energy marine environment.
Advantages
This application reinforced several proven advantages of Proserve’s grouted fabric formwork approach in large-scale offshore bridge construction:
- Adaptability to complex bed profiles
- Surface-only installation enabling rapid, safe execution
- Controlled uplift and internal pressure to prevent rotation during grouting
- High-performance contact interface with no reliance on compaction or blinding layers
- Seismic and hydrodynamic resilience, supporting the design intent in a cyclone-prone zone
The success of this system on the NRL viaduct foundations highlights its applicability to future offshore or marine infrastructure projects requiring precise structural placement, reduced marine risk, and engineered reliability.