That's hard to say, what class of soil it is, around here there's clay and gravel mix, and shale. If you were putting up a building with spread footings, soil classification would have to be figured out to meet the loading, but with a parking lot, you would think no more than a foot, or just the topsoil to the undisturbed. Auto traffic and maybe an occasional truck ? If its unstable you could take more out, use fabric, but no need to waste money if not needed. I would strip the top, see what it does, hit it with the vibratory roller, see if it pumps water or is unstable. If not, I've done a lot of jobs without fabric in this area, the soil is plenty stable enough, its just the top soil that won't hold up, so it has to be removed. I'll show some photos of one small job I did, was on fill, the house was built in a low area, and I did hit water and had one area pumping up, it was a soft area for sure, I could not even load out the spoil with the front bucket, I had to stockpile it, and load with the hoe, onto a tri-axle. Seemingly nasty soil, deep, water, can't take it all out, so I took a 12"-18" out, then brought in gravel, then Item #4, rolled each lift and when I found that one soft spot, I dug it out, hit water, so I had to put some broken concrete in there, just like rubble, and it stabilized easily, no pumping. This as I recall was some really soft material, I could have made a real mess on this job if I did not know what I was doing, I did put a drain pipe in that daylights at a small stream. I even found an old cut off stump, roots in place still, left it, was hard, almost tipped me over when the one wheel hit it and the other sank. I had to plank the driveway to get the trucks in to load them out, the material I loaded out settled flat it was so wet. I stockpiled good material on the street and used the bucket to haul all the material in, lot of material went in here, I may have taken more out, can't recall, might have sent about 3 trucks out with wet spoil. One of the more undesirable soil/fill areas I've worked on, its been there 9 years now, they paved over it with binder then a wear course, no settling at all. I used no fabric either. Soft area was in front of that little garage, this small roller did a decent job of packing it in though, was not too surprised it held up well, but you never know, just did what would do on any jobsite when I was an operator, having lots of experience in soft, wet, and muddy sites, hate working in those conditions, but there are times you must and you do need to know what you are doing to some degree LOL ! I really enjoyed this kind of work, sure as heck wish I could do it for a living, given I've had no luck with finding work suited to my background. The smaller jobs that pay on time were always good, they don't take weeks or get too complicated. I used to have a great arrangement with a local rental house, most if not all surface work, lower risk, customer pays via credit card, machine is delivered, I do the rest, charge labor and materials, no heavy mark up, just don't barter my rate to run the machine, the rest was a savings.
Enough about me, LOL, sounds like you may not need to remove too much, these jobs are fun because its just moving material in and out, packing and grading etc.
