Project Description
Value engineering foundation solutions for Assheton Sheltered Accommodation, Porchester
This project was to provide 60 sheltered housing flats for social rent on an existing site that had 20 flats and bedsits. The new development was being built by Feltham Construction, and the architects are MH Architects, based in Chichester.
Value Engineering Opportunities
We were asked to look at the scheme at tender stage to identify value engineering opportunities in the foundations as the superstructure solution was already well developed by the architect, and the programme didn’t allow for a wholesale change. As such, the superstructure was to be a load-bearing masonry building. The proposed trench-filled foundations were particularly wide to accommodate the loads and needed to be deep due to the significant depth of made ground (where the natural ground has been significantly altered by the placement of artificial materials or fill). Foundation depths were estimated to vary from 1m to 3.1m.
Ground Improvement v Piled Foundations
We considered piled foundations as a solution, but there were concerns that the site was over an aquifer (a natural source of drinking water) and piling might create a preferential pathway, where contaminated water could make its way down into the aquifer. Maps from the Environment Agency confirmed the site was in fact on the border of the aquifer.
Given the variability of the material across the site and the unknown depth to the white chalk deposits (the material we were targeting under the made ground), we proposed that the head deposits made ground be subject to ground improvement techniques to increase the bearing capacity at a higher level.
Another concern of ours was the level of the water table, given the site’s proximity to the coast. A ground improvement solution would mean significantly reduced excavation depths, so we would stay above the water table.
By using a ground improvement option instead of piles, we avoided digging foundations below the water table and any need to investigate the aquifer further and obtain additional permits.
Project Team
Client: Fareham Borough Council
Architect: MH Architects
Contractor: Feltham Construction
Efficiencies in the build programme
Whilst the superstructure was well developed, we worked with the contractor on where they could make efficiencies to the build programme and modify the design to speed up installation. It was a tight site, so what could we do in stages, and what could we change in the structural design to aid that efficiency?
We identified that there was a central link area between the two larger four-story ‘wings’ and adjusted the design to build the two four-story buildings with the crane situated between them. In this way, the crane could then pull out to build the single-story glazed link connecting the building.
When we reviewed the design of the cantilever balconies and proposed a solution to support these on the pre-cast planks as opposed to additional steel work internally. This removed a significant amount of steelwork, another efficiency and cost-saving for the client.
If you have a project or community building that you are making alterations to, want to extend, or are concerned about its structural integrity, then give us a call on Witney (01993 225085) or Southampton (02381 920656) or email mail@swjconsulting.co.uk
Photo credit Feltham Construction
