CM is using 30% compaction factor. That's what I use for gravel, sticky clay is not that good. Loading with an excavator, that dirt is as loose as it can be in the box. If it's chunky/slabby to boot, 50% might be reality. Another factor is who did the survey for the estimate? I have NEVER had an import fill job come out even factoring in 30-40% onto the estimate for compaction. Uneven terrain can make you look silly real quick. Sometimes I think engineers subtract 20% from their estimate to screw the contractor.
I use a bank CY which is the same as the compacted volume of the fill material. Posted that on my iPhone and I should've went into more detail.
When I estimate a job I do my own take off on yardage, I never just use the engineers estimate. I'll use the engineers estimate, if there is one, only to check my numbers against.
So let's say I estimate a job to need 1,000 CY of import and I know what the density in PCF of the material I'm importing from a proctor. The heavier the material the lower the swell or compaction rate will be, conversely for the lighter material. The engineered fill material in my area averages 115-125 PCF.
If the job takes 1,000 CY, I'll add a waste factor to the number anywhere from 15-40% depending on the accuracy of the plans, job site visit, etc. After that number is calculated which is the job total, then I use the 14 CY per tri and 10 CY per tandem to calculate how many truck loads I'll need, figure the time, dirt cost and loading, then you have a cost per CY which will get the standard project mark-up O&P (10-20%) on top of that. Depending on the material, I'll adjust the yardage hauled on the trucks which is always adjusted down not up.
As you said Shimmy, importing fill on a hard contract can eat your lunch if you don't estimate it closely. I obviously prefer the jobs that pay by the CY of import or export but those jobs are few and far between.
