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For those of you that do subdivision work...How do you go about calculating earthwork volumes?

I'm not talking about the actual steps taken within Land Desktop to perform the calculation...more so the method used to arrive at your final quantities.

I have seen people simply calculate the overall volume and that's it (maybe with some manual calculation using area in roadway to subtract/add cut or fill at sub-grade or use a total area disturbed to calculate topsoil to be stripped) and then compare to a contractors quantity to see if they're in the "ballpark" and then use the contractors quantities for an engineers cost estimate.

Around here, we tend to be a little more particular. We have gone so far as to lower existing surfaces a certain amount to simulate a surface stripped of topsoil...or lower a proposed surface a certain amount to sub-grade and use parcels to calculate earthwork volumes within streets. We may choose to use a number of parcels in roadways and on lots to calculate volumes in different scenarios...i.e. Ex. Surface (adjusted for topsoil) -vs- Prop. Surface (adjusted to sub-grade) with 10% compacted fill in roadways, Ex. Surface (adjusted for topsoil) -vs- Prop. Surface with 10% compacted fill in areas from the roadway to the rear of building pads, Ex. Surface (no adjustment) -vs- Prop. Surface with no compaction in rear yards. It is not uncommon for us to take trench dirt into account as well. As you can probably imagine, this method can get a little "intense" sometimes (not to mention what happens if our quantity differs from the contractors).

Where we have run into trouble recently is when we model a surface to sub-grade (in roadways) for purposes of preliminary design...and then when the project is all but submitted for approval, we go back and perform final earthwork volume calculations and try to compare "apples to apples" and need to start all over again with the final proposed surface.

I am just curious to know what types of methods/processes others have used to calculate earthwork volumes for an entire site or a building phase within a site.

Also...if any of you have similar experiences with Civil 3D, what is the workflow like when trying to accomplish these tasks?

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Wouldn't you create a new surface with your proposed information, then compare the existing & proposed surfaces using terrian model explorer? Then run the reports? That's what we do.

I really shouldn't answer a question with a question, huh?

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:Cheers:

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Phil,
I have done my quantities a few different ways. I have run my prelims using the subgrade approach while taking into account the fact that when they cut for subgrade, they have a 4:1 max slope (in these parts anyway) from the subgrade cut to the front of the pad. It took a couple times back and forth with the grading contractors to see why our numbers were so much different from their's. Some of them would only run the slope to 20' behind the ROW, while others would go to the pad. Then we would subtract the overex for each of the pads, figure in subsidence and shrinkage and take .5' off the entire site for 'Grubbing' and scarification.
In other regoins, they just want the 'Raw' numbers, no transformations or adjustments. And then there are others that want you to include the Shrinkage adjustments directly into your output tables.

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