COP29 – Using ground improvement to reduce the quantity of concrete entering the ground

As COP29 continues this week, we remain focused on how we can continue to improve the efficiency and sustainability of our projects. The use of concrete contributes a significant proportion of carbon emissions attributed to the construction industry each year. Finding solutions to reduce the need for concrete can therefore provide more sustainable developments; one such example is the use of ground improvement. Senior Geotechnical Engineer, Rose Ashmore, shares our recent experiences.

CampbellReith’s multidisciplinary team is always looking to provide sustainable alternatives to traditional (and carbon intensive) practices. A recent example is our involvement with a commercial development on the outskirts of Frome, Somerset. Due to the presence of poor and variable Made Ground across the site with underlying shrinkable clays, the recommended foundation solutions presented in the scheme ground investigation report was a suspended slab supported on deep trench foundations or a piled foundation solution.

Our structural and geotechnical teams undertook a value-engineering exercise and determined that the installation of vibro-stone columns would allow a more economical and sustainable foundation solution as it would allow a ground bearing slab and shallow foundations to be adopted.

Vibro-stone columns involve the use of a specialised rig that displaces the soil using a ‘poker’ creating a void. The void is then backfilled with aggregate that is compacted in stages. These columns provide vertical inclusions of material with higher stiffness and shear strength than the in-situ soils. The foundations can then be placed as pads or strips across these columns which provide an increased bearing capacity.

CampbellReith worked with a specialist contractor, GeMech Ltd, to carry out preliminary on-site testing to confirm the suitability of vibro-stone columns and to validate the design. Working in conjunction with the specialist allowed the assessment of risks (such as encountering obstructions that might result in premature refusal) to be establish prior to the commencement of the main works, helping to improve efficiencies and minimise plant mobilisation.

By implementing a vibro-stone column solution beneath the building footprints, shallow pads and strip footings could be constructed at 1m below ground level. This reduction in the depth for the foundations significantly decreased the quantity of concrete used. In addition, as the installation of the stone columns does not produce any spoil, and a reduced depth of excavation was needed for the foundation pads, minimal waste material was created therefore significantly reducing the volume of soil sent to landfill.

Coordination between our structural and geotechnical teams resulted in us providing the client with advice that led to a more cost-effective and sustainable foundation solution. By undertaking early-engagement with the specialist contractor, we were also able to undertake additional investigations to refine the design and methodology, reducing the programme and cost risk of the ground improvement regime.