concrete parking lot

[johnhan76]

I am designing a concrete parking lot for a restaurant. The natural ground is a heavy clay with a seasonal highwater table that is approx. 6" below the surface. several questions that I hope someone could help me with.

1. Is it ok to cut into the soil or do I need to fill everywhere. The site is 1.5 acres.

2. If it is not ok to cut into the soil due to high groundwater, what is the maximum seperation between the top of the seasonal high groundwater and the bottom of the stone base. (if a stone base is necessary)

3. What do you recommend for a typical pavement design. The one that I am proposing is 6" of concrete, 6" of stone base and finally a compacted subgrade.

Thanks in advance for you help.

 

[GeoPaveTraffic]

The answer depends on many things in addition to the information you have provided. What part of the country is this project located? In particular is there EVER the potential for the ground to freeze? What kind of life does the owner of the project want from the pavement?

There are other questions as well that are not coming to mind at the moment. I personally, would not put any pavement within 6-inches of the normal high groundwater level. If the site conditions were such that it could not be avoided, I'm not sure what those conditions could be; I would most definitely put in a drainable rock base with French drains connected to the stormwater system for the parking lot. I would also put a very good filter layer between the soil and the rock base, a filter fabric would not be adequate and properly designed filter layer should be used. If the site freezes and the water level is with in several feet of the pavement you have major problems.

By the way, what is being done with the building if the water level is that high?

 

[johnhan76]

The site is in coastal Georgia - frost is not an issue down here. The building will be 2.5' above natural ground so it is ok. THe first grading plan I did had every area way above the seasonal high groundwater mark but the cost estimates were too high. Currently, the areas around the inlet are below grade and everything else is fill. I am deciding whether or not to put the rock layer under concrete. The soil is a heavy clay. (35% clay)

 

[Focht3]

GeoPaveTraffic is right - you need separation between the stone and subgrade. Lime is not equivalent.

But you don't have to use a stone layer; in fact, I don't recommend it unless it is the local practice and the paving contractors are familiar with it. Raise grade with a low plasticity silty clay or sandy clay (7 < PI < 20) as needed. Use deformed bars, not wire mats, for reinforcement. Put in an extra inch of concrete, be sure you have excellent joints, and put a spun-bonded needle punched (non woven) filter fabric beneath the joints. The filter fabric will prevent subgrade pumping - major cause of RC pavement failure. Dowel across the joints and use a high quality joint filler. This pavement will last a lot longer than the RC/rock section.

If you use stone and leave out the filter fabric, expect the pavement to begin failing within two months of the onset of use...

 

[johnhan76]

focht3, do you recommend the filter fabric underneath the entire pavement or just under the joints. I question the sandy clay suggestion. Everything that I have read suggests granular material becasue Clays near subsurface water has the potential to pull the water upwards with capillary action. Sands generally are stronger too. Thanks for the input.

 

[Focht3]

johnhan76:


Filter fabric beneath the joints -

I understand your concern about clay fill; but remember that you have a clay subgrade, too. Capillary action will also occur in the native soils...Actually, this isn't a significant concern. RC pavements are quite common along the Gulf coast, with no significant problems with capillarity.

And sand fill will allow water to penetrate faster and farther. Not a good idea, particularly with a good RC pavement design.