aggregate over aggregate - can I layer these?

awl51 · Oct 2, 2008

Always enjoy the wealth of information here. I appreciate any insight about what to do here.
I built a simple pad at our weekend place on which to park a double-axle boat trailer during winter. Boat and trailer weigh 3500 pounds. The pad is 10 feet wide by 20 feet long.
I am using a somewhat sloped area of the yard for the pad, such that there are 3 sides enclosed with 4x4 pressure treated lumber, and the entry is at grade - just back the trailer right up and onto the pad. The idea was to use 3/4" crushed rock - which should interlock nicely - over road geotextile cloth, with depth of the fill averaging about 6-8 inches, and maybe 2 inch minimum at the front "lip". I have a small plate compactor that I can borrow if needed to tamp anything down.
The local gravel company up there does not work weekends and does not deliver without someone present, so I phoned in an order for 3/4" crushed rock to them and asked my mom to be there when it was delivered to the pad area. When I got up there last weekend, I was disappointed to see that they had dumped a load of 3/4" screened stone instead of crushed rock. I wasn't sure what to do, so I spread it out over the road cloth to the depth of the sides, and tried compacting it every couple inches. It wasn't very successful - the boat trailer's narrow tires just plow the gravel out of the way and sinks in. My truck's wide-profile rear tires are just able to sit on top of the stone without sinking in, but the fronts start sinking with even the suggestion of a turn.

So, what to do?
One thought is to compact it as best I can, then top it with some asphalt road mix - but I'm not sure that I'll be throwing good money after bad.
Another thought is to dig out some of the stone with the FEL (but not too deep, I don't want to snag the cloth), and then replace it with 3/4" crushed rock. If I did this, should I put another layer of the road cloth between the two different aggregates, or would they tend to stay separate?

ampsucker · Oct 2, 2008

i can only share what i've done in slightly similar circumstances but not exactly the same. you have a deeper base of "clean" rock then i've had and the size is smaller.

around here, it's common practice to lay down clean 2" run as a base that packs down into the clay and mud when you drive over it to make an effective road base. then you lay smaller 1" base or "dirty" rock (with the crusher fines) on top which packs into a smooth driving surface.

you having a deep layer of clean will give you excellent drainage, but also much movement which you don't want. i think you need some fines to lock things together. i would suggest sand with the hope that somebody who has tried this in the past with real experience would chime in and comment if it actually works. that could be the easiest option. add sand, vibrate it down into the voids with the compactor and then lay a couple inches of dirty rock over the top to get a good driving surface. this should be manageable by hand with the small area you have.

otherwise, if you can use the clean rock somewhere else (muddy spot you want to put a road, drainage culvert or perf pipe, etc.) you can pull out all but the bottom few inches and then lay in the dirty rock on top and you should be good to go.

i would also suggest that once the dirty rock is spread, you wet it down and pack it with the plate compactor.

i wouldn't try to maintain two separate layers or add any more textile material.

others with more experience may disagree.... ;-)

amp

Skyco · Oct 2, 2008

I've found that rock all one size will not pack. You need from fines all the way up the maximum size you want to allow it to pack.

I'm not sure I understand what you mean by 3/4 crushed rock vs 3/4 screened stone, sound like the same thing to me, unless you mean the screened stone was gravel or river rock all the same size....note- gravel and crushed stone are two different things to a quarry although to the general public they are erroneously thought of as the same. The terminology also seems to vary somewhat regionally.
You need 3/4 minus crushed stone/rock that includes down to the fines to pack, if you didn't tell them the minus part you probably got what you ordered.
Gravel (rounded natural uncrushed stone) will never pack well IMO. If you have all one size now sometimes bringing in course sand and mixing it with the rock to form a packable surface.

schmism · Oct 2, 2008

i would get a load of river sand delivered. (hard to mess that up)

then pull out about half the gravel, put down a layer of sand ontop of the stone, drive on it, work it in, then another layer of stone, another layer of sand etc.

the small sand should settle into the gravel and should act like the "fines" your missing.

this should mean you have some material left over. feel free to continue to add a mix of the stone/sand over time as the boat trailer settles the material.

if you have access to water you can water the sand into the gravel also

radioman · Oct 2, 2008

I agree with the others here. Since you have already tried spreading out the stones with what you have already. Since its only 3/4 crushed rocks, it should be easy to skim off the top, say go down couple inches at least. Order crusher run this time that has the mix you need and spread out to cover what you skimmed off. Compact that and let it get rained over a few times and it'll be like concrete floating pad by then.

Gary Fowler · Oct 2, 2008

Sounds like you have screened river rock which is mostly rounded shapes. You need some crushed angular material in order to lock all this together. Get some crushed stone and a vibraplate to compact it. Stay away from river sand as it will not lock together since is is also mostly round particles just like your river rock only smaller, much smaller. Go with radioman and get the crusher run and spread it on top of the existing gravel then vibrate it in with several passes of the vibraplate. Water it in good and let it set for a few days to dry out and it should hold together well. For an even firmer topcoat, try adding a few bags of portland cement with the crusher run and compact then water in.

KeithInSpace · Oct 2, 2008

The screened stone will, by definition, not compact. The intent of the screened stone is as a drainage layer. Not 100% sure how to remedy it except to remove it. The only other thing would be to somehow get the screened stone on the BOTTOM of the sandwich, THEN woven geo fabric (not non-woven), THEN the crushed stone.

Adding asphalt directly to the screened stone will only result in the flexible asphalt moving around as the stone beneath it moves around.

As others have suggested, you could also try adding sand or portland cement to the stone and mix/vibrate the stuff together. You need to fill all the voids to get the stone to stop shifting around. If you don't get the stone to stop shifting, ANYTHING you add on top of it will be a waste of money.

awl51 · Nov 4, 2008

Thanks, all. I read through all the replies, and there were good ideas in each. Here's what I did: I removed the top two inches or so of the screened stone; compacted the remainder; and then put a layer of woven geotextile fabric down.

I 'gently' deposited a new top layer of 1 1/2" crushed rock with the loader, roughly levelling it with an iron rake as I worked my way forward across the pad. Until the top layer of crushed rock was in place, I tried to keep front wheel turns to a minimum to avoid ruts. Once the top layer was in place I ran the compacter over it.

The new top layer is extremely solid and can stand up to narrow tires, turning wheels, etc., without developing ruts. Even though the crushed rock is sort of "floating" over the lower layer of screened stone, that lower layer is contained by the 4x4 sides, the geotextile fabric, and the weight of the top layer of crushed rock. Bottom line is that it works and the effort to correct the problem wasn't too bad.

As an aside - as I've read these forums over the years, I'm amazed at the number of different terms and modifiers that contributors use to describe types of aggregate materials: for example, clean/dirty, minus/plus, DG, crushed ledge, screened, crusher run, 57s, ABC, traffic bond, etc etc . There are regionally different names for the same material. Anyone know of a definitive guide? And more to the point - are there good guides as to "what to use where"? I've seen some materials descriptions posted on different quarry websites, but they seem to be limited to what the particular quarry is selling.