You would need to be more specific as to what surface you want to apply this Crushed Bluestone to. For example, a stable base would cause less flattening in turn you may need less bags when go to flatten or roll with heavy roller or other. If using on an unprepared or recently dug up disturbed base the amount of bags you would need would depend on how you plan to prepare the base before applying the Crushed Bluestone then go to flatten. I know even on my driveway if I fill small areas such as where my car tires sit and drive over, in one season with snow melt and other such as rain it does need filling again every other year due to there is a bit of standing water there and my gravel drive has been there for 50 years with it being re-done twice. I will be looking to see if Pavestone answers your question soon so I can also learn.
Yes you can use this as a leveling stone.
Approximately 40 to 50lbs.
It is very similar in size and is angular and can be used for compaction. Thank you for your inquiry!
It is mostly gray
It can be used, but will be difficult to walk on when barefoot.
About one inch long with random shapes and always look good when wet.
This is a crushed Bluestone with approximately 3/4" stones. You should not have an issue with your french drain but if your still concerned then you may want to go with a smaller sized gravel such as pea gravel.
27 cubic ft=1 cubic yard of gravel which is 13.5 bags. Your dimensions yield a total of .57 cubic yards of gravel needed at 8" depth. Your project will need 8 bags of the crushed blue stone. Any measurement is never exact in measuring the ground depth. A section of your trench might be +or - the 8" depth. Having said that, add plus 1 bag for a total of 9 to purchase.
For a 15' L wall that is 8' H, I would recommend getting it engineered. But on a standard 15' L at 4" D of subbase, you would need approx. 20 bags of material. I hope this helps and thank you for your inquiry!