R400 Peat Pilot Scheme



Brief Description:
This project, delivered on behalf of Offaly County Council, involved the full-depth reconstruction of approximately 1,750 metres of roadway along the R400 Regional Road in the townlands of Knockdrin and Derryiron, Co. Offaly. The existing road was constructed over peat, leading to ongoing settlement and structural instability.
Project Sector:
Road Infrastructure
Year Completed:
2024
Client:
Offaly County Council
Designer:
Offaly County Council
Location:
R400 Rhode, County Offaly
Project Role:
Main Contractor & PSCS
Detailed Description:
As part of the works, traffic management was implemented in accordance with Chapter 8 Guidelines under a full road closure to ensure safety and efficiency. Upon mobilisation to site, we excavated and disposed of 19,500 m³ of unsuitable material off-site to reach suitable formation level.
To provide structural integrity and long-term performance over peat ground, a multi-layered geotechnical solution was adopted, including:
- 19,000 m³ of 6F2 capping
- 18,000 m² of Naue Biaxial Combi-Grid 40/40 Q6
- 36,000 m² of Naue Biaxial Secugrid 40/40 Q6
- 43,600 m² of Stabilenka 200/45 woven geosynthetic reinforcement
These geosynthetics were installed in varying layers throughout the pavement build-up to reinforce the structure and distribute loading more effectively across the weak subgrade.
Following ground improvement, the pavement layers were constructed with:
- 3,056 m³ of Clause 804 granular sub-base
- 12,159 m² of 60mm AC 20 dense binder course (70/100 pen)
- 4,066 m² of SMA 14 surface course (PMB 65/105-60, 40mm thick)
- 8,093 m² of double surface dressing
Additionally, all associated drainage and accommodation works were completed as part of the contract to ensure the longevity and proper function of the road structure.
This scheme represents a successful pilot initiative by Offaly County Council, demonstrating how innovative ground engineering techniques can be applied effectively to regional roads constructed over peat, with a view to informing future works across similar terrain.
