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Hong KongEarthwork quantities and compaction
Volumes are calculated in cubic yards at 27 cubic feet each. Excavated soil swells when loose and shrinks when compacted, so bank, loose and compacted volumes all differ for the same material.
The arithmetic is easy. The states of the material are where the questions are.
Three volumes for one pile of dirt
| State | Means |
|---|---|
| Bank | In place, undisturbed, as measured in the ground |
| Loose | Excavated and in a truck, which is more volume |
| Compacted | Placed and compacted, which is less volume than bank |
Excavate a cubic yard and you haul more than a cubic yard. Place and compact it and it occupies less than a cubic yard.
A hole needing 100 cubic yards of compacted fill needs more than 100 cubic yards of bank material to supply it. Ordering to the compacted figure leaves the job short, and questions are built exactly there.
The conversion
Twenty-seven cubic feet to a cubic yard. Every earthwork and concrete calculation runs through it.
Length times width times depth in feet, divided by 27. Depths in inches convert to feet first, and forgetting that is the other common error. Lifts too thick is the failure.
Compaction
Specified as a percentage of a laboratory maximum density, tested in the field. Achieving it depends on moisture content, lift thickness and the right equipment for the soil. Twenty-seven. Learn it.
Placing lifts too thick is the usual failure. The top compacts and the bottom does not, and it passes a surface test while settling later. It settles later.
Cut and fill
Balancing them on site avoids hauling material in or out, which is often the largest single cost in earthwork.
Common questions
How many cubic feet in a cubic yard?
27, and every earthwork and concrete calculation runs through it.
What are bank, loose and compacted volumes?
The same material in place, excavated, and placed and compacted. All three differ.
Why do fill quantities catch people?
A hole needing 100 cubic yards compacted needs more than 100 cubic yards of bank material to supply it.
How is compaction specified?
As a percentage of a laboratory maximum density, tested in the field.
What is the usual compaction failure?
Lifts placed too thick, so the top compacts and the bottom does not, settling later.