Sub base saturation

[Davidevans94]

Hi, first post and thanks for such a comprehensive resource. I finally plucked up the courage to block pave my old concrete drive and started work a few weeks ago. Drive is around 6.5m long and slopes down towards house about 0.7m so roughly 1 in 9. I've dug out approx 240mm into firm clay and placed and whacked the first 75mm of type 1 dolomite yesterday. Problem now is that following a night of heavy rain I have a soft, wet spot around a metre in diameter a couple of metres from the bottom of the drive. The dolomite is almost fluid and standing on one spot raises the adjacent dolomite. I scraped away some material today expecting to find a soft spot, but the substrate was firm clay. Any ideas what the issue is and how to resolve it? One thing that struck me was that there seem to be a lot of fines in the dolomite so I wonder whether sieving out some fines and replacing the soft spot with a more granular mix may be a possible solution? I don't want to place the second layer of dolomite until I've resolved this particular issue. Job is otherwise going well, albeit slowly, thanks to the detailed information on this site.
Many thanks
Dave

[seanandruby]

Will be like that on clay because water got no where to go. Did you do a percolation test to see if how fast it drains. You need fines to bind the dpt1. You would of been better off pulling off some clay and putting on crush first. You will need to put in a linear drain.

[Davidevans94]

Thanks for your reply Sean. In my ignorance I wasn't aware of the need to do a percolation test as I assumed that the water would run naturally downhill. It just seems odd that the fill's saturated in one spot mid-slope rather than at the bottom. Can I dig out just the wet spot and add crush (I assume that this is a coarser grade of fill), or could this cause differential settlement? Thanks again.
Dave

[seanandruby]

Just dig out the wet clay yes. A few days of s'shine will dry out the type 1. Did you place a membrane betwixt the clay and stone?

[Dave_L]

What's a problem today won't be a problem tomorrow when its sealed over and dried out.

[Davidevans94]

Hi Sean, I haven't used a membrane. Would this have helped?
And thanks for the advice Dave L.
Dave

[seanandruby]

It's necessary if you have a sound sub soil not liable to let the mot sink in and become fluid