[H]omer wrote:
:: Spider wrote:
::
::: I wonder how deep you're excavating, and how close to your house.
::: I must assume that your house is built on the same heavy clay
::
:: I'm afraid that it certainly looks that way.
::
::: ,and I am concerned about subsidence if you materially change the
::: surrounding soil.
::
:: Me too.
::
::: I don't mean to frighten you, but if I have awoken any doubts,
::: please consider consulting a surveyor (and, perhaps, your building
::: insurer) before it's too late.
::
:: You have, and you have, in that order.
::
:: It had occurred to me before actually. The property developer was
:: brought to task by other residents over several issues, including
:: flooding. Basically they built the entire site on a known ancient
:: floodplain, and within the first year nearly every house was under
:: 3ft of water. They then "diverted the source upstream", but still
:: the flooding came. Eventually the council took drastic action to
:: dam the source, and we haven't seen any flooding since.
::
:: Everyone round here is aware that the developers are a bunch of
:: cowboys. The state of our 'new' houses when we moved into them was
:: pitiful, so it didn't really surprise me to discover we were
:: sitting on top of a clay pit. I was angry, but not surprised.
::
::: Hope everything goes okay and you get the garden you crave for.
::
:: Well there's always Water lilies, I suppose.
::

If you contact building control[1] at your local council they may be able to
tell you on what foundations your house is built....from what I can glean
from your posts it sounds like infill, thousands of tonnes of clay over the
top of what was there before, if this is the case, it's highly likely your
house is built on piles (concrete stilts which go down very deep, usually
until bedrock is found)...once all these piles are in place, a reinforced
concrete strip is then poured on top and the house built on that, other than
that it could well be on a raft - one huge block of concrete, usually at
least a metre deep and the entire floor area of your house, the idea with
this is that if anything moves, it all moves.


[1]
There may be a search fee, but I'd do this before contacting your insurers,
they will double your premium at the drop of a hat.

--
"Our enemies are innovative and resourceful, and so are we.
They never stop thinking about new ways to harm our country
and our people, and neither do we."
- George W. Bush, 5.8.2004