We are in the process of re-building our drive. We have decided to use gravel with one of the plastic grid options that are now available.
We have excavated the area to a depth of around 26cm, allowing 6-8cm for the final layer of sand, grid and gravel and 20cm for MOT grade 1 hard core.
The problem we are having is that almost no-one will provide a weight to volume conversion ratio. I know we have a volume of approximately 3.12m(cubed). The best I've come up with so far in my local area was 2.3 tonnes to 1m(cubed). This equates to roughly 7.2 tonnes of aggregate. Does this sound about right?
The second problem is that we assume this ratio is that it is for uncompressed aggregate. Is there a guideline for approximately how much it will compress by? The area is approx 6m (long) x 2.5m (wide) x 0.20m (deep). We assume we'll need to order extra to allow for being compacted, the question is how much more, 10%, 20% etc.?
The third and final question, should we consider putting in any type of under ground drainage beneath the hard core? I only ask because I saw it as a recommendation on one of the installation instructions for the plastic grids we were investigating.
Thank you for your assistance with this.