Simplifying groundworks design

Wherever it is appropriate, we try to simplify scheme designs to reduce the cost and minimise the environmental impact.


NPS Group's specialist subsidiary Robson Liddle demonstrated this on a project in Truro, Cornwall. The residential development at Newbridge Lane, Gloweth was on a sloping site. Our initial involvement was for site investigation and some of the sub-structure design, but this developed into a wider review of the design of the groundworks.


Parts of the site had a 1 in 4 slope, and the original design made extensive use of concrete retaining walls at the boundaries between level changes. While this was a quick and simple design, it was fairly expensive and required large quantities of materials to be imported to the site.


We proposed an alternative based on analysis of our site investigation results. Using software called ADAMA ReSlope, we determined that the soil conditions would allow the safe use of ground slopes up to 1 in 2. By carefully re-designing with steeper slopes, we were able to eliminate most of the concrete retaining walls. The new design needed more soil, but we were able to make use of material excavated from elsewhere on the site. Achieving this 'cut and fill balance' within the development avoided the need to dispose of that material off-site at considerable cost.


The success of our input led to our being asked to use the same approach on other areas of the site. Overall we were able to eliminate 70% of the concrete walls from the design. The total cost saving was in the order of 15%. Just as importantly, we significantly reduced the environmental impact of the scheme by removing the need for materials to be transported to and from the site.