I am currently excavating some footing for a two-storey extension and they are to be dug at 1750mm. Whilst digging we have gone through the clay and hit a poor sub-soil which is not very stable causing the sides to collapse, I have been told that this could be "river -bed" but as I live up the side of a hill I am not so sure anyway please could you offer some advice as to what the sub-soil could be and how I can get around the problem of the sides collapsing?
Bob, what does the building control officer have to say, they usually offer good advice. Where does the 1750mm come from, it sounds a bit too deep, unless the ground is quite bad? Choices you have are 1) earthwork support (shutter). 2) Batter the sides and then shutter. 3) change foundation design (Structural engineer required). Could you carry out any tests to determine founding layer properties, once again BCOfficer could advise.
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