Using retaining walls to maximise housing development land

Prime housing development sites rarely come without challenges. Common issues include sloping areas of ground that must be held back and soil that must be stabilised before construction can commence. While retaining walls are a tried and tested solution, they can be costly and significantly reduce a site’s viability, so choosing an effective solution without impacting profitability is key. Here, Alex Walther, Head of Technical Sales at Tobermore, looks at some recent projects to find out how housebuilders have used the Secura Grand retaining wall solution to unlock the potential of their developments – on even the most challenging of sites.

Stabilising a steep railway embankment without piling or habitat destruction

Some sites require significant work before development can be undertaken, including specialist equipment or piling work which can not only prove cost prohibitive but also contribute to habitat loss and increase the development’s embodied carbon. This was the dilemma for Keepmoat Homes when they needed to stabilise ground against a steep bank caused by a railway cutting at a site in Gedling, near Nottingham, that was due for residential development.

Sheet piling at the bottom of the steep bank was considered, but access was proving difficult and would require removal of woodland at the base of the slope. Secura Grand allowed ground retention to take place at the top of the bank. This saved considerable cost, reduced earthworks and the need for specialist piling operatives and machinery on site.

Tom Vallance, Associate Director at Independent Design House, a global engineering design consultancy specialising in temporary works with considerable experience in Tobermore retaining wall design, described the challenges faced on site and how they were overcome: “In the design of the bank retaining solution, we had to deal with a railway cutting, which was a steep, almost vertical slope and the proximity to the railway. The cost of the original suggestion, a major exposed sheet pile, was prohibitive. By designing a special foundation detail, utilising a reinforced concrete shear key into the bedrock, we were able to utilise Secura Grand.

“We sent our civil engineering external works technical drawings to Tobermore for assessment, and they helped us to understand the challenges on site and the viability of Secura Grand for our project. The follow-up design and engineering support, and the final estimate that included value engineering opportunities for the complete solutions, saved us time and eventually a significant amount of money.”

Developing around a watercourse

Natural features can also add complexity to site development plans, as was the case for Bellway Homes. The company needed retaining wall designs for the Snelsmoor Village development on the outskirts of Derby. The retaining walls had to perform two critical functions. Firstly, they had to overcome reduced stability caused by a watercourse running through the centre of the site. Secondly, they needed to enable piled house foundations to be drilled on the high side of the retaining walls.

The company selected Tobermore as their retaining wall partner. The company provided Bellway with an extensive suite of online design tools backed up by technical expertise and design support to help design a viable solution with Secura Grand.

The system was used to plateau build zones early in the site programme and allowed Bellway to come in at a later date to pile house foundations through the reinforced soil wedge. Secura Grand proved a technically sound solution that not only supported the overall site programme but was also financially viable.

Improving connectivity to support regeneration plans

It’s not just the housing development sites themselves where ground needs stabilising and strengthening. Work can also be required to provide critical infrastructure and access, as was the case for the Sunderland riverside development plan. Tobermore were approached by Fairhurst to provide a value-engineered option to a new bridge linking Sheepfolds Stables to the Stadium of Light in Sunderland. The original proposal by Fairhurst involved a costly reinforced concrete structure with piled foundations and a lightweight fill between the two structures.

Tobermore put forward a value engineered option utilising the Secura Grand reinforced soil retaining walls over a cast in situ concrete culvert. The aim was to reduce excavation at the foundation level of the wall due to contaminated land surrounding the bridge. A mixture of variable poor ground, unknown soil parameters and contamination proved to be a challenging design.

Settlement was a large concern from the wider design team due to variable founding levels of the wall. Secura Grand’s flexible nature and reduced bearing capacity requirements to reinforced concrete allowed for a cost effective and efficient design.

Now completed, the Secura Grand wall stands at 9m high and 5m wide, demonstrating the scale of the solution.

Building on sites with underground voids

Land with dissolution features such as cavities from soft chalk, sinkholes, swallow holes, or uneven rockhead must be stabilised and strengthened prior to construction; otherwise, it could lead to costly repair and remediation work. At the White Rose Park development on the site of the former Royal Norwich Golf Club, Persimmon Homes had opted to pile the House foundations and screen walls.

However, a faster, more cost-effective solution was required for the retaining walls around the site. Tobermore’s Secura Grand was specified because the only site preparation required was minimal local rapid compaction ground improvement. The flexible nature of the solution allowed for a reduced foundation detail when compared to traditional masonry structures on site. This not only helped the program on site but also reduced build costs.

Ultimately, every developer wants to maximise the available space on prime development land; however, some solutions are cost prohibitive. As we have seen, the Secura Grand solution from Tobermore is flexible, cost effective and doesn’t require specialists to install, allowing housebuilders to overcome a wide range of different challenges.

Are you planning a housing development with challenging ground conditions? Tobermore’s Retaining Wall Design service provides expert technical support to help identify practical, cost-effective retaining wall solutions for your project. Discover Tobermore’s Retaining Wall Technical Design Service.