Ground type

[David WE Roberts]

Many thanks for all assistance to date.

One thing I did on advice was to buy the 'Building Construction Handbook' by Chudley & Greeno. A very fact filled book, but one which sometimes raises more questions than answers. For example on Page 201 there is a table for Ground Type.

One column is for 'Field Test'. For Clay and Sandy Clay under 'Stiff' it says 'requires pick or mechanical device to aid removal'. Further down under 'Loose' it says 'Can be excavated by spade'.

Now my experience from gardening and general digging is that the ground consistency varies throughout the year depending on how wet or dry the ground is.

For example, this summer when I was putting in new fence posts I had a really hard job digging the holes and used a pick and a mattock to loosen the soil. This winter with all the rain I am digging out the ground for the concrete slab for the shed base using a spade and a shovel and it is easy to dig.

So which should I use for the 'field test'?

Depending on the weather the same soil could be anywhere from 'Stiff' to 'Very soft'.

In waterlogged conditions the only ground hard to dig would be mainly gravel and/or rock.

Ho hum

Dave R

[Roger Chapman]

I don't know for sure but would suggest that builders would be interested in the nature of the subsoil rather than the top soil.

In normal circumstances you are likely to get at least a foot of top soil and at that depth the difference in consistency will be much less through the seasons.

[mogga]

Dig down and post a photo.

You'll know if it's clay.

[David WE Roberts]

Unfortunately by the time I had worked my way through the book I had removed the topsoil and so the subsoil in the area has been treated to a good watering.

Given the recent wet weather most soils are waterlogged to a considerable depth. I could dig a test hole elsewhere to the depth of the foundations - however I suspect that everywhere is soft and wet at the moment.

Just musing, really, on how easy it is to confuse things rather than simplify them with additional information. The book also suggests a concrete raft as a solution for footings on a poor substrate. As I am laying a concrete raft as the simplest way of constructing the base then this seems to cover off any issues over the suitability of the subsoil.

I see the weather is changing to very cold just in time for me to lay the concrete base. Dry would be good; overnight frost is less attractive.

[David WE Roberts]

I know that it is sandy clay - it is just that sandy clay covers the range from Stiff to Loose and as far as I can see the consistency will change with the water content.

Clay is well known to be hard as rock when dry and squishy when wet. Ask any gardener ;-)

Fortunately the ground is more sandy than clay so does not suffer from the 'heave' you can get with clay soils (as found elswhere in the town).

As stated in my other response, my chosen footings are 'concrete raft' which is suitable for poor substrate so I should be O.K. whatever the classification of the soil.