Our drive was laid with incorrect materials and I'm now looking to find an
effective way to fix it.
We're on clay and the layup was a Terram membrane, then subbase with
depth varying from about 150 mm to 500 mm in places, and a plastic
honeycomb product filled with gravel on top.
The problem is that the wrong subbase material was used - single-size
rounded 40 mm. The subbase has moved due to vehicle movements,
resulting in the honeycomb breaking up in places. It's like walking on
a pebble beach. So we need to replace both.
The obvious method is to take up all the 40 mm subbase and replace it
with angular graded material such as Type 3 to maintain the drainage,
replacing the honeycomb on top. Contractors have suggested it isn't
necessary to take up all of the old material but just take up 150 mm,
or even less, and put graded material on top.
I don't know what is adequate and would welcome your advice. Of course
the last thing I want is to redo everything and end up with a similar
problem again in a few years. Other possible thoughts include the use
of another membrane below the new subbase and/or trying to fill the
existing subbase with sand or dust to increase its load-bearing
capacity. What's a good idea and what's not?