Basal Reinforced Platforms
The use of high strength geotextiles or geogrids to transfer vertical and lateral embankment loads onto a piled foundation. Also known as Load Transfer Platforms (LTPs).
Instability/unsuitability of foundation material and possible differential settlements can be addressed by the construction of a basal platform that spreads, spans or dissipates the construction loads into the ground. Basal platforms are typically used in construction of infrastructures such as roads and railways.
Reinforcement of the basal platform with geogrids or geotextiles enables it to accommodate higher loads whilst providing opportunities for reduced thickness of high quality fill layers.
Reinforced basal platforms can be built over piles installed in soft ground. The piles transfer the load of a structure (typically: an embankment) to a stiffer stratum underlying the soft ground. However, piling is an expensive technique: by using high strength geosynthetics, the load can be more uniformly distributed over the pile caps and the required number of piles may be reduced, with considerable cost savings.
Geogrid and geotextile reinforced platforms might be used to avoid subsidence and sudden settlement of structures built over mining or naturally occurring voids such as solution features.
The A249 Isle of Sheppey scheme in Kent included widening of the route and a new bridge. The route runs on flood plains comprising soft alluvial material. Short construction times were achieved at tender stages by using Geosystems. Where the embankment on the approaches to the new bridge exceeded 2.5 m height, the contractor proposed to build a piled embankment with a geosynthetic reinforced Basal Reinforced Platform (BRP) to transfer the embankment loads to the piles.
A dock wall for a new oil tanker berth was to be built over very soft alluvial soil at the Royal Portbury Dock in Bristol. Piling was to be used to create the foundations for a vertical retaining quay wall. The use of a basal reinforced platform using high strength geogrid to reinforce fill placed on top of precast driven piles reduced considerably the number of piles required. ICE members or NCE subscribers can access this case study from the New Civil Engineer's website.
- BS EN 1536:2010 Execution of special geotechnical works. Bored piles
- BS 8006-1: 2010 Code of practice for strengthened/reinforced soils and other fills
- CIRIA Publication SP123 Soil Reinforcement with Geosynthetics
- TRL Contractor Report CR341 Highway embankment over soft compressible alluvial deposits: guidelines for design and construction, Crowthorne, 1994
- TRL Project Report 71 A guide to accommodating or avoiding soil-induced lateral loading of piled foundations for highway bridges, Crowthorne, 1994
- Maccaferri Basal Platforms information page (http://www.maccaferri.co.uk/PAGES00161.html)
