Practical (Geotechnical) Magic

We were called to the rescue of a local home owner recently. They had been told, by both Building Control and their builder, that they needed to make substantial improvements to their existing foundations in order to be able to add a first floor extension to their property. The existing foundations had been signed off by Building Control, a number of years previously, but were considered insufficiently deep and wide to support the additional loads of the proposed extension.

To add to the problem, the existing foundations were off-set from the line of the existing walls, but there was no indication to suggest they would be inadequate. When we asked what information Building Control had used to reach their conclusion all we got in response was ‘it’s just not what we usually see’. We thought we could (and should) do a little better than that…

Given our knowledge of the local geology, we knew the property was likely to sit directly onto the bedrock chalk, which being ‘rock’ is usually pretty strong (maybe the clue is in the name?). We carried out some low-cost field tests adjacent to the existing foundations and used these data to complete an evidence-based geotechnical design. We then worked with the project’s structural engineer to confirm that the existing foundations were more than adequate to support the new loads.

The cost of carrying out the testing and subsequent report was less than 10% of the cost of the previously proposed ‘necessary improvement works’. Not only that, they yielded a significant time saving. A win the for the client and a win for us – sometimes it’s just nice to be on the right side of common sense.