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Mostly due to the ground not matching what the geo charts said, and proximity to trees.
The engineer really should have been aware of this in their design.
Also this is why it pays to have appoint local authority building control officer when you do a basement as in some boroughs they want to inspect every pin before its poured. It beggars belief that they didn't get the LA/their approved inspector to come out and inspect the first one at least to pick up this issue (haven't watch the programme).
Speaking as an Engineer, this intrigues me no end!