A. Jay Meunier responds: Don't bother re-excavating those areas to compact the fill in lifts. Instead, grab a hose and lightly saturate the areas with water. You want the soil to be damp but not full of water. Let the water percolate down through the soil to eliminate air pockets, then run the compactor over it. Do all of the areas once, then start over again. This should do a good job of providing a stable subgrade. When you're pouring the slab, lay a grid of 1/2-inch-by-6-foot rebar (two pieces in one direction, two perpendicular) across those areas as additional cheap insurance.
Jay Meunier is an estimator for Pizzagalli Construction in Burlington, Vt., and the former owner of a residential concrete business.
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