earthwork puzzle 1

[efejr28]

Hello everyone! I am working with an earthwork for a rough grading set of plans. The site is divided into two parcels. I first calculated and earthwork for the whole site; existing ground against rough grade (1), existing ground against finish grade (2), and rough grade against finish grade (3). After that, I divided the earthwork 3d polylines into the two parcels, one file per parcel. After running earthworks for each parcel separately, I found that the sum of the earthworks for each parcel (rough grade against finish grade) does not match the earthwork for the whole site. Even the earthwork for the whole site, (1) plus (3) does not match (2). Any suggestions or same experiences?

Thanks
pD

 

[bltseattle]

One thought, how does the modeling tool represent the parcel edges? If a cut/fill slope is extended by the tool beyond the edge of the parcel, there could be overlapping "volumes" between the two parcels, depending on the computation method(s).

To get a handle on the discrepancy you've observed, I would use the earthwork modeling tool to produce a plan drawing that shows the depth of cut or fill at each point on a grid (cut/fill tiks), then look for busts/inaccuracies in the numbers. You should see discrete zones of cut and fill for each scenario, and should be able to add together numbers from the two interim grading steps to check the number on the exist-to-final version of the plan. I would also try to plot sections showing the 3 surfaces so you can verify that the rough grade surface is the same in both scenarios.

A final check would be that the compaction/expansion factors are incorporated to reflect realistic earth volumes.

 

[SteveWarfle]

pD.....I would guess that the discrepency has something to do with your boundary, and how your sections are "daylighting". You don't mention what software you are using, but it really doesn't matter. Each earthwork software package, wether CAD based or specialized varies in the way the perimeter is supposed to be entered.

In our product, which uses triangulation, the connection of surfaces gets pretty aggressive. For example, imagine a "C" shaped site. A surface would be created filling the interior of the "C". If this happens on both existing and proposed, the results can be more cut & fill than reality. This same phenom exists to some degree in cross section or grid based products as well. To prevent this, some means of limiting the calculation of disturbance is neccesary.

In most software products, there is some facility to limit the calculations to a specific area. In our software, InSite SiteWork, the perimeter is entered, and proposed is automatically daylighted to the drawn line, and calculations are prevented outside this area. This works in most cases, but in the situation where a match line exists, such as where your individual plans go together, this would not be desirable. Having the proposed surface seek existing at a match line wouldn't work.

Most software programs require you to do something different at this type of boundary. We allow the boundary type to be switched from an automatically daylighting type to what we call a "cut-off" boundary, to allow for the correct calculations. You need to investigate what you are using and find out what you are supposed to do in "daylighting" or "match-line" situations.

Over the years we've had situations where two customers using the same or different products have gotten two different answers. In evaluating the differences, it usually comes down to a different interpretation of site condition (ie. Stripping depth, paving materials thickness, topsoil rplacement requirements, etc.) or the limits of work (boundary). Since you seem to be doing a straight two surface calculation, it should be the second case.

If you have anyway of looking at small areas of the site individually, you can usually analize where the problem is pretty quickly.

I hope this helps.

Steve Warfle
Product Manager
InSite Software Inc.
1(877)746-7483