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yacobyishak (Civil/Environmental) (OP)
21 Dec 11 18:40
I am going to observe as a building construction inspector the cut  that is going to be done in the near future for a parking lot. I was instructed to perform a proof rolling on the cut. I thought you were supposed to do proof rolling to see if there was either a rut or pumping before you do the compaction test using a nuclear guage. Do you need to perform a proof roll observation on a cut?

Helpful Member!  Ron (Structural)
21 Dec 11 20:30
Yes.  Just because the grade is cut, does not mean that the exposed surface is compacted nor is it necessarily uniform.  Proofrolling is still a reasonable requirement.

Further, cutting overburden can expose capillary rise or be in closer proximity to capillary rise of the piezometric surface. Proofrolling will expose such influence and allow you to deal with it.
BigH (Geotechnical)
21 Dec 11 23:09
It will also expose soft spots that might be present - organic deposits, old stream beds, etc. - what will you use for proofrolling - a loaded truck or a compactor??
yacobyishak (Civil/Environmental) (OP)
22 Dec 11 21:25
I thank Ron and BigH,
My question is whether you do proof-rolling on a cut that is going to be filled with another base material. It was decided that a certain depth was to be removed and then filled and compacted to a given proctor value. I need to check the proctor value on the fill using the nuke guage. I thought proof-rolling was to be done on  the compacted layer before the nuke guage. I am going to use on this compacted layer a loaded dump truck (20-30 ton). I am not sure what kind of proof-rolling truck to use on a cut.  
jgailla (Geotechnical)
23 Dec 11 8:16
yacobyishak,
You should be doing the proofroll on the exposed subgrade before the placement of fill.

This is perhaps more important than proofrolling the surface after placement of fill.

If you have good quality control during fill placement, you have a pretty good idea that the fill has been placed properly, compacted, and free of deleterious materials.  

However, you do not know this of the subgrade.  As Ron and BigH point out, there could be bad material in the subgrade.  Proofrolling will expose these areas of bad subgrade and indicate where further undercutting should be performed before fill placement.

The equipment used is the same regardless of whether you are proofrolling subgrade or fill.  A loaded 20 ton dump truck should be adequate.
Ron (Structural)
23 Dec 11 8:19
No.  As BigH noted, do the proofrolling before filling so that you can identify soft or yielding soil conditions.  That way if you have to remove the poor soils identified in the proofrolling, you don't have to also remove fill material that was just placed.

As for compaction of the exposed cut, sample the soil and get a moisture-density relationship (Proctor) test done in the lab, then do the nuke density testing, followed then by Proctors for the fill and subsequent density testing in each lift of fill.
jrm73 (Geotechnical)
29 Dec 11 15:39
I have done more of these projects than I count where we remove soil and replace it for various reasons. We prefer to proofroll with a loaded dump truck to locate weak areas or potential pumping.  It has been my practice to begin backfill after the proofroll passes.  I believe the more you dig around and manipulate the soil with proofrolling and compaction before backfilling, the greater is the chance of problems such as rain delays.  Practically speaking, if you have borings, you probably already know if you are going to be in a stronger or weaker deposit at the bottom of the excavation.  If you are near the water table, the more you work the soil, the more water you will bring to the surface and initiate pumping.  My belief is that if you can get 95% density or greater on the first 6 inch to 8 inch lift, then the subgrade is adequate.   

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