2016
Dawlish, Devon
Redrow Homes
Harris and Harris Construction Ltd
Wardell Armstrong
Reinforced Piled Embankment Solution for Soft Ground Road Crossing in Dawlish, Devon
Global view of the site – Piling configuration
Installation of the longitudinal layer of ParaLink®
Installation of the transversal layer of ParaLink®
Layers of ParaLink® within compacted 6N material
Final compaction operation for the basal reinforcement
Finished surfacing on the road
Challenge
Redrow Homes proposed a new residential housing development on land off Shutterton Lane, Dawlish, Devon, comprising a mix of private and affordable homes, landscaped gardens, public open spaces, and associated infrastructure. A critical element of the scheme was the construction of a new road connection linking two sections of the site, requiring a culverted crossing over an existing brook.
Site investigations revealed significant geotechnical challenges at the proposed crossing location. The ground conditions on both sides of the brook were highly variable, with very soft soils including peat deposits. These weak, compressible materials presented a high risk of settlement and instability, making conventional road embankment construction unsuitable. Without a specialist ground engineering solution, the long-term performance and safety of the road infrastructure would be compromised.
Solution
To overcome the poor ground conditions, a reinforced piled embankment solution was designed, incorporating a geosynthetic load transfer platform to ensure effective load distribution and ground stabilisation. This approach enabled loads from the road and embankment to be safely transferred through the weak soils onto underlying competent strata via piles.
A 300 mm thick load transfer platform was constructed using granular material compliant with Specification for Highway Works (SHW) Type 6N, providing high strength and stiffness where required. Below this, lower-strength site-won materials were utilised for the remainder of the embankment, optimising cost efficiency while maintaining performance, except within the carriageway where higher specification materials were retained.
The design of the load transfer platform was carried out in accordance with BS 8006-1:2010, using Marston’s formula to determine load distribution. A surcharge load of 30 kPa was applied at road level across the full embankment width to simulate traffic loading conditions.
To enhance structural performance, the platform incorporated two orthogonal layers of high-strength geosynthetic reinforcement installed directly above the pile caps. In the longitudinal direction, perpendicular to the culvert alignment, ParaLink® 450 was specified to provide the required tensile strength. In the transverse direction, parallel to the culvert, the design requirement of 500 kN strength was achieved using two layers of ParaLink® 250. This configuration allowed the necessary bond length to be achieved within the available footprint.
This engineered solution delivered a robust, cost-effective, and compliant method for constructing a culverted road over very soft ground, supporting the successful delivery of residential infrastructure in Dawlish while mitigating geotechnical risk.
Used Products
