On 23/03/2015 08:56, Brian Gaff wrote:
Its very hard to disguise where some concrete structure has been, even if
you fill the hole up and grass it over the way it grows seems to be
different to the rest of the site quite often. Also it tends to change
height over time, sometimes its higher sometimes lower.My late father did
this with some solid features in our garden, you could always tell the
outline of them.
Brian

While sealed hollow concrete structures do want to float on underground
water and may rely upon the weight of whatever is in them to keep them
in the ground, I suspect that was mainly due to the soil around it
changing volume. Clay is particularly liable to change volume as its
water content changes.

--
Colin Bignell