Parking Lot- Sand Or No Sand?

gdavis

Hi all. I'm a newcomer to this site, and a relative newby to the excavation industry. I've owned my own construction company since 1991 in Western Michigan, and have always owned several pieces of misc. earth equipment. With the rececnt changes in the building economy I ran across an excavating company for sale which I bought all the equipment from. Now I'm trying to diversify my construction business through excavation.

To my question: I was hired to install a gravel/crushed concrete parking lot approx. 60' x 100' in front of a metal building. This parking lot needs to hold up to heavy equipment and minor parking traffic. The soil consisted of 8-10 inches of heavy top soil with grass growing, on top of solid and tight clay base. My initial thought was to strip 12" from existing grade, provide positive drainage grade at this level, and replace with 6" of sand (for better drainage) and top with 6" of crushed concrete. Is this necessary on a solid clay base? or are there better methods. Also, what do you do when you run into a "muck hole" in a clay bed such as this? Do you dig out the wet material, and if so what do you fill with? It seems that sand fill in a clay hole would only hold water more. Thanks in advance for your help, I have learned alot already from this site.

Dirtguy

I would say strip of the vegetation and install all crushed concrete (10"-12"). In our area the crushed concrete is a little cheaper than sand and has larger aggregate which will provide more strength to support the heavy equipment you referenced. Sand will have a tendency to "pump" if it has too much moisture in it. If you can't get the subgrade to dry and firm up by ripping and recompacting, I would suggest mixing in some hydrated lime or portland cement. But keep an eye on your cost, it may be cheaper to just increase the thickness of the crushed concrete. Application rates for lime are about 6% or about 4% for cement. This equates to an application rate per 6" depth of aproximately, lime 30# per SY, cement 20# per SY.

GOOD LUCK!

rino1494

Around here, we use shale for our sub-base and then top it with modified.

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biggixxerjim

Bump. Sand doesnt make a good binder and crushed agg. tends to turn into slop once a decent anount of water is added. Id say a coarse shale or even large clean stone, topped with road stone

farmboy555

#3 or #4 stone for base. It will let water drain and hold up the equipment parking on it.

denick

g,

We would strip the topsoil. Grade the clay sub base to be even in bearing capacity and pitched if possible. If there is a soft or wet spot. If really wet and sloppy dig out the mud and dump a load of blasted rock in it and work it into the clay until it has the same consistency as the rest. You can place a layer of stabilization fabric over the clay if you feel there is a bearing problem. We would use a very bony bak run gravel for the base and 3/4" process on the top 3". Or a layer of road base which is a material with fines and up to 5" rock in it. and then the processed material. If you suspect water trapped under the pad a 4" pipe dissecting the area with some stone around it could help.

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tgeb

I think the 12" undercut is good, I would eliminate the sand all together.

I would use what we call here CR-6, or crushed run, compacted in lifts.

Soft spots, we have just under cut an extra foot or so, and fill and compact with the same material.

As Nick stated above, if water is a problem, pipe it out.

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www.gebcon.com