The 15,000 Loose Yards That Weren't a Surplus
A highway embankment needs 9,000 compacted cubic yards (CCY) of fill. The contractor is using on-site cut material - a silty sand with a measured swell of 25% (bank to loose) and, based on the project's Standard Proctor curve, a shrinkage factor of 15% (bank to compacted). End-dump trucks are permitted 15 loose cubic yards per load. On day three the foreman reports that 15,000 LCY have been excavated and tells the inspector the cut is 'already 6,000 yards over what the fill needs,' and proposes to waste the balance in a stockpile that sits on a future storm-drain easement. Separately, the inspector notes a 100-ft section of prepared subgrade pumping under the loaded trucks after a rain.
1. How many bank cubic yards must be borrowed from the cut to build 9,000 CCY of fill, and how many truckloads of true surplus material must leave the site?
Read the worked answer
Convert the fill demand to bank measure. Shrinkage of 15% means 1 BCY yields 0.85 CCY in place:
- BCY required = 9,000 CCY ÷ 0.85 = 10,588 BCY
Find the surplus. 12,000 BCY has been excavated (15,000 LCY ÷ 1.25 swell = 12,000 BCY).
- Surplus = 12,000 − 10,588 = 1,412 BCY
- In loose measure for hauling: 1,412 × 1.25 = 1,765 LCY
- Truckloads = 1,765 ÷ 15 = 118 loads
The check that matters: every cubic yard placed is measured compacted, and every cubic yard hauled is measured loose. Both numbers must be brought back to bank measure before they can be compared or subtracted.
2. Evaluate the foreman's claim that the cut is 6,000 yards over. What is the error, and what is the practical consequence if the inspector accepts it?
Read the worked answer
The foreman subtracted 9,000 CCY from 15,000 LCY. Those are three different material states, and 15,000 LCY is only 12,000 BCY - not 15,000 BCY.
Restated honestly: the excavation is 1,412 BCY over, about 12% of the cut, not 40%.
Consequences of accepting the claim:
- Roughly 3,500 BCY of material that the embankment actually needs would be wasted, then re-imported (at purchase plus haul cost) - a classic unbalanced-earthwork claim.
- The stockpile on the storm-drain easement would have to be moved a second time, and the easement would be obstructed during construction.
- The inspector's authority here is documentation, not argument: record cut quantities, truck tickets, and Proctor results, and require the contractor to justify any waste in bank measure.
Recommendation: reject the waste proposal, keep the surplus as a documented stockpile in a permitted area, and confirm the shrinkage factor against the actual field density curve rather than the design assumption.
3. The subgrade is pumping under haul traffic after rain. Should the fill be placed anyway, and what are the defensible options?
Read the worked answer
No. Pumping means the subgrade soil is saturated and has lost shear strength; placing fill on it traps a weak layer that will produce settlement and shear failures later, and no amount of compaction on the lift above will fix it.
Options, in order of preference:
- Dry and recompact. Scarify, aerate, and retest density and moisture. Cheapest if the weather allows and the section is small (100 ft).
- Undercut and replace with select granular material or a stabilization layer, then place a separation geotextile before the embankment.
- Chemical stabilization (lime or cement) if the soil is a plastic clay and time is short.
- Suspend haul over the section and route traffic around it - traffic loading accelerates the failure.
Undercut depth should be set by proofrolling until the subgrade is non-pumping, and the replacement material should be compacted to the same specification as the embankment. Document the extra excavation as a differing-site condition if the moisture is weather-driven and the contract assigns weather risk.