Tim Lamb wrote:

I suppose you should take off the
topsoil (mud) put down Terram membrane and put in 6" or so of scalpings
or similar. In wet weather, mud will still be carried onto the new
surface but water should drain easily.

I agree with Tim.


We've done this on a sandy bridleway, limestone was not an option because of
leaching into an sssi, so we excavated to ~400mm, laid terram with the
wings laid out to the side, filled with 200mm andesite(sp??) granite
scalpings, folded the terram back to cover the scalpings and form a pillow
with overlap and re laid the topsoil. We only formed a 1.5m strip because
the terram is 4.5m wide and to allow overlap but the same could be done
with one overlapped joint under and one on top. The track then looks fairly
natural, is slightly raised to allow run off and has stood up quite well.
If the soil has little bearing capacity because it is clay or silty I
wouldn't worry about reinforcing it with some more soft scalping or even
pebbles as long as they embed in the soil. It's small sharp chips that you
need a boy scout to remove isn't it?

This will all depend on where the area drains to so consider putting a
wavinflow perforated pipe under the joint with the concrete to take the
water.

AJH