When we start a project, we are looking at the architect’s information, topographical survey, and site investigation data. Information from soakage tests, CBR (California Bearing Ratio) testing, and general ground conditions gives us an idea of what we’re actually building on.

We are based in Southampton and so local projects in the wider Hampshire region tend to be on areas of chalk, which has a tendency to be of variable condition. Whether we’re dealing with structured chalk or structureless chalk, it can really affect what you end up putting in there.

Where a site investigation would have helped
On one of the sites that we’re working on currently in the South Winchester area, we started the project without the results of a site investigation.

It looked to be a very simple project.

As we were in Winchester, it was assumed that we’d be able to use soakaways as the main method of surface water discharge. Once we received the site investigation, it was discovered there were dissolution features in the ground, where the chalk is structureless and as water passes through it, the ground has the potential to just dissolve.

That meant we had to have additional offsets from the building to put the soakaways in. We couldn’t fit soakaways in, so we had to find a new way of discharging water. Unfortunately, there are no surface water sewers because we’re on chalk; everywhere is on soakaways. All the ditches around us are on a higher level, so we can’t actually discharge to the watercourse.

Eventually, after looking through every available option, going to Southern Water and the planning authority, the solution we devised was pumping surface water from the site up a couple of 100mm to be able to get into the existing ditch and away.

It’s one of those projects where, if we’d had that site investigation from day one, we would have known that we needed to pump the surface water into the ditches, rather than going through six different variations of design, speaking with different people and organisations, which delays the project and adds cost to the project.

It’s things like that, that really affect the smooth running of a project.

If we are provided with, or can get those investigations and data first, we can see what the risk is, what’s happening and we can identify any issues early so redesigns are not necessary.

If you think we could help, please give us a call on Witney, 01993 225085 or Southampton, 02381 920656 or email mail@swjconsulting.co.uk.