I am working on a taxiway project at a regional airport. The spec calls for 19" 2A sub-base, 8" FAA spec sub-base, and 6" asphalt. We dug the area out and have to compact the virgin dirt to 95%. The material is clay and is very tight but moist. The first half we dug out was able to air out for a weekend longer than the second half. We were able to get to the 95% compaction but the optimum moisture is 15%, we are getting anywhere from 17-25% moisture. All tests are with a nuclear gauge. They wouldn't approve the grade because of the moisture. We used a disc to help dry it out, and the first half we dug out the disc barely broke the surface it was that hard. We had rain in the forecast and wanted to get it covered, so graded it up and rolled it. The roller was bouncing on the grade, you literally couldn't drive straight the drum was bouncing so much. So we drove a loaded tri-axle on it and no movement. The moisture was still high but they approved and we were allowed to put on the sub-base.
-So today I put a 4" lift of stone on it. We need 100% compaction and optimum moisture is 6.9-8.3%. The material was coming in dry so we wet it down with the water truck and roll it. We got the 100% compaction but the moisture was low. It was at anywhere from 2%-4%. We wet it down some more, the water is puddling on top of the stone, the stone then starts to get mushy from all the water and the moisture percentage barely moved, but they are reluctant to allow another lift because we do not have the optimum moisture.
The tester (from a 3rd party but hired by us) says the moisture number is to allow optimum compaction kinda like a lubricant to allow material achieve optimum compaction, but we achieved the specified compaction without the moisture, but the job engineers say we need to achieve the moisture level to meet the spec.
-If we got the compaction why would we need to wet the material down just to meet the spec? Are we wetting it down just to make it wet? Won't it dry out eventually anyway? My brain tells me the water is going to go somewhere, and gravity will make it find the clay underneath, that was already to wet for their liking.
Yesterday we were trying to dry out because the dirt was way to wet, today we are spraying hundreds of gallons on the stone that is 4" above the the dirt.
Anyone been in this predicament before, or know enough to explain the logic to me? Or is it the normal situation where the engineers seem to be in out in left field?
Thanks for any input.
-So today I put a 4" lift of stone on it. We need 100% compaction and optimum moisture is 6.9-8.3%. The material was coming in dry so we wet it down with the water truck and roll it. We got the 100% compaction but the moisture was low. It was at anywhere from 2%-4%. We wet it down some more, the water is puddling on top of the stone, the stone then starts to get mushy from all the water and the moisture percentage barely moved, but they are reluctant to allow another lift because we do not have the optimum moisture.
The tester (from a 3rd party but hired by us) says the moisture number is to allow optimum compaction kinda like a lubricant to allow material achieve optimum compaction, but we achieved the specified compaction without the moisture, but the job engineers say we need to achieve the moisture level to meet the spec.
-If we got the compaction why would we need to wet the material down just to meet the spec? Are we wetting it down just to make it wet? Won't it dry out eventually anyway? My brain tells me the water is going to go somewhere, and gravity will make it find the clay underneath, that was already to wet for their liking.
Yesterday we were trying to dry out because the dirt was way to wet, today we are spraying hundreds of gallons on the stone that is 4" above the the dirt.
Anyone been in this predicament before, or know enough to explain the logic to me? Or is it the normal situation where the engineers seem to be in out in left field?
Thanks for any input.
Compaction- Soil Density and Moisture
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