Fill is being placed at a moisture content well below optimum. What is the most likely result?
- The fill pumps, ruts and sticks to the drum on every roller pass
- The required density is hard to reach even with extra passes
- The fill reaches a higher density than the lab maximum
- The fill needs thicker lifts to compact properly
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B. The required density is hard to reach even with extra passes
Dry soil has too much friction between particles, so the roller cannot pack it to the target density; water is added and mixed in. Pumping and rutting are the signs of fill that is too wet, not too dry.
Reference: Soil compaction: moisture-density relationship
Which compactor is best suited to compacting lifts of cohesive clay fill?
- Vibratory plate compactor
- Smooth-drum vibratory roller
- Walk-behind power screed
- Sheepsfoot (padfoot) roller
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D. Sheepsfoot (padfoot) roller
The feet of a sheepsfoot roller knead and shear clay, compacting from the bottom of the lift up. Vibratory smooth drums and plates work by shaking particles into place, which suits sands and gravels but does little in clay.
Reference: Earthwork equipment selection: cohesive soils
Clean sand and gravel fills are compacted most effectively by which action?
- Kneading
- Static weight alone
- Flooding only
- Vibration
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D. Vibration
Granular particles rearrange into a denser packing when shaken, so vibratory rollers and plates are used. Kneading action is what works on cohesive clays, which do not respond well to vibration.
Reference: Earthwork equipment selection: granular soils