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Design of an OPC retaining wall foundation on challenging ground, to support a brownfield housing development in London featured in Ground Engineering Magazine.
Client: Bellway London Partnerships
Principal Contractor: Statom Group
Supply chain: Andun Engineering Consultants, Geosynthetics & Geoman
Photo credit: Ground Engineering Magazine
Scope of Work
Andun’s scope of work was to design the foundation for a 6m high, 364m long and 11m wide geogrid reinforced wall as part of the Barking Riverside Project.
The Barking Riverside mixed-use development is being built on a 180ha brownfield site on the north bank of the River Thames.
One of the housing plots on the western end of the site was on a sunken piece of land that had to be raised by 6m. A reinforced soil retaining wall was needed over difficult ground conditions to contain the raised plots.
Site Constraints and Challenges
The key site constraint was the very challenging ground conditions on site that feature extremely low strength cohesive soils as well as the areas of peat.
Site investigation identified a 2m layer of peat that was excavated to allow for the creation of a wall foundation. The groundwater levels were also high, further reducing ground-bearing capacities and making foundation construction difficult.
Statom remediation and environmental director Sean Deloughery explains that Andun were engaged to design the wall foundation as a specialist ground engineering solution.
“They ran tests to decide on the best option, which ultimately involved digging down and removing the peat layer and then re-engineering the existing soil back under where the wall was being constructed”
Retaining Wall Foundation Design Considerations
The Andun project team worked closely with Statom, Geosynthetics and Geoman throughout the design process. Geosynthetics and Geoman assisted in the design and construction of the geogrid reinforced structure.
A number of different foundation designs were initially considered including a granular raft, stone columns, a deeper reinforced earth wall and a piled reinforced concrete wall.
Given the site challenges, an Ordinary Portland Cement (OPC) chemically stabilised soil raft foundation was chosen as the most appropriate design solution.
This option significantly reduced the amount of material imported onto site as a large portion of the foundation uses the already in situ soil.
A stabilised platform is stronger than a traditional imported granular foundation, which means that the amount of muck away was decreased twofold. This solution lead to programme, cost and carbon savings.
Photo credit: Ground Engineering Magazine