A client of mine wants to use an aggregate(stone) in a parking area meant for empty RVs and Tractor Trailer (10 total per a day) and about 30 box trucks per day. He does not want to use asphalt pavement. The current subgrade soils are soft to medium stiff clays and silts. Does any body have a experience with using geogrid to stabilize this type of subgrade prior to placing stone(gravel)? what type/thickness of stone(gravel)should be utilized? I think he does not want to use cement or lime.
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Utilization of aggregate/stone for a parking lot instead of asphalt 1
- Thread starter Parkerlax
- Start date
is he wanting an actual pavement design or generalized recommendations with no particular performance criteria?
as far as geogrids in "shallow" pavement fixes with performance criteria requirements, i'm not a fan; however, they do work sometimes (sometimes they don't). for "shallow" fixes in pavements, i usually see the contractor spend a lot of time and money fooling with stabilization geosynthetics (and hoping that it works) that could've just as easily been done with a little extra over-excavation, lime/cement, aggregate, compactive effort, etc.
my guesstimate for a real design would be (assuming the subgrade is reasonably stable): 24-36" aggregate total = 16-24"+ of #34 sized aggregate atop filter fabric and capped with 8" graded aggregate base (well compacted in thin layers-same as in pavement base course layers). if the client were mine and they wanted a more "hopeful" recommendation, i would tell them that they can make the pavement last as long or short as they want. it all boils down to $$$$. 6 inches of gab atop whatever is there might last a few years before complete failure but it also might have lots of potholes after only six months.
as far as geogrids in "shallow" pavement fixes with performance criteria requirements, i'm not a fan; however, they do work sometimes (sometimes they don't). for "shallow" fixes in pavements, i usually see the contractor spend a lot of time and money fooling with stabilization geosynthetics (and hoping that it works) that could've just as easily been done with a little extra over-excavation, lime/cement, aggregate, compactive effort, etc.
my guesstimate for a real design would be (assuming the subgrade is reasonably stable): 24-36" aggregate total = 16-24"+ of #34 sized aggregate atop filter fabric and capped with 8" graded aggregate base (well compacted in thin layers-same as in pavement base course layers). if the client were mine and they wanted a more "hopeful" recommendation, i would tell them that they can make the pavement last as long or short as they want. it all boils down to $$$$. 6 inches of gab atop whatever is there might last a few years before complete failure but it also might have lots of potholes after only six months.
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Would it be possible to strip the topsoil and root mat and scarify and recompact the clayey/silty subgrade? If so, you can take a bulk sample of the clayey/silty subgrade and run a CBR test (i.e., to get the CBR for 95 percent compaction). From this you could then design the aggregate pavement section using the CBR and the structural support values of the aggregate.
Here's where the body is burried: If you use aggregate for the "paving" surface it will readily infiltrate surface water, which in turn will allow for the traffic to disturb the compacted subgrade. Two ways to handle this: use subdrainage or thicken the aggregate to provide enough headroom to keep the dynamic loading away from the saturated surface.
We have a local RV dealer that has the same setup and they are O.K. with their gravel stagging area for RV storage.
Good luck. My gut tells me you'll need 12 to 18 inches of dense graded aggregate on a recmpacted subgrade and may not even need a geotextile.
f-d
¡papá gordo ain’t no madre flaca!
Here's where the body is burried: If you use aggregate for the "paving" surface it will readily infiltrate surface water, which in turn will allow for the traffic to disturb the compacted subgrade. Two ways to handle this: use subdrainage or thicken the aggregate to provide enough headroom to keep the dynamic loading away from the saturated surface.
We have a local RV dealer that has the same setup and they are O.K. with their gravel stagging area for RV storage.
Good luck. My gut tells me you'll need 12 to 18 inches of dense graded aggregate on a recmpacted subgrade and may not even need a geotextile.
f-d
¡papá gordo ain’t no madre flaca!
theCorkster
Geotechnical
Pakerlax;
I've prepared gravel pavement design for clients somewhat similar to yours. A couple of things to keep in mind:
1. Look at geogrids rather than geosynthetic fabrics; they tend to provide more strength at lower strain and can reduce rutting;
2. The aggregate layer should be drained. Rain will saturate the subgrade and possibly the aggregate. The site should be sloped to drainage points prior to placing geogrid or aggregate; and
3. Maintenance; if you use a poorly graded aggregate you'll likely have surface rutting, and periodic regarding will be required. Sharp turns to access the area will result in more rutting as well.
Make sure your client's expectations for the performance of an aggregate pavement are not the same as for asphalt or concrete.
Good luck!
If you want to use geogrids, I suggest that you take a look at and their free SpectraPave software which can be used to evaluate unpaved roads and geogrids to provide subgrade stabilization. I have completed many projects with their biaxial geogrids and my clients have been extremely satisfied with the results. Good luck.
Actually, many geotextiles can provide higher strength at lower strain and the geotextiles can provide separation and drainage that geogrids cannot. Stress-strain is dependant on the polymer and the way the material is manufactured. The Tensar material referenced earlier actually has low strength at low strains compared to other material on the market. For gravel roads you are often better served using a geotextile.
Check out for more info on geosynthetics. The HP geotextiles are high strength reinformcement for subgrades. You can find a local rep or engineer that can help you with their products and a gravel road design.
Check out for more info on geosynthetics. The HP geotextiles are high strength reinformcement for subgrades. You can find a local rep or engineer that can help you with their products and a gravel road design.
I might be a few months late here, but think about these things when using fabric of any kind below base courses.
Some day there may be the need to re-grade the area. Once a grader blade catches the stuff, you won't like the result.
Also, any buried utilities now or later?. Try digging thru the stuff then. No fun.
Some day there may be the need to re-grade the area. Once a grader blade catches the stuff, you won't like the result.
Also, any buried utilities now or later?. Try digging thru the stuff then. No fun.
DarthSoilsGuy
Geotechnical
way too easy and very much not fun.
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