I will be performing density testing for backfill being placed behind foundation walls and I have been fighting with the contractor over lift thickness. The contractor wants to place the backfill in 12 inch lifts; however, I don’t want the contractor to do so because the excavations are so narrow the only compaction equipment that will fit is a small jumping jack (like a Dynapac LT 6000 – static weight 150 lbs, impact force 3,300 lbs) so I don’t think he will be able to meet the 95% Modified Proctor density requirement. Does anyone have experience as to how thick of a lift you can actually get compaction on in this situation? The backfill soil is generally sand with a lot of silt (USCS classification SM). I am hesitant to even let the contractor attempt a thicker lift, because it will be extremely difficult to remove the soil once it is in place without significantly widening the excavation. Anyone experience of advice that anyone has would be greatly appreciated.
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