Negative cut and fill volumes using sample lines

[Anonymous]

I am creating volume reports using sample lines and computing materials. For some reason I am getting negative values for some of the volumes. Does anyone have a fix or explanation for this?

Does anyone know how civil 2016 calculates the volumes for each sample line?

-Kyle

[Joe-Bouza]

Reverse your base and compare surfaces

[Anonymous]

I dont believe thats the problem. The cumulative volumes im getting for cut and fill are close to what I find when I look at a volume surface comparing the two surfaces. Ex: Surface Volume Cut/Fill = 100/1000 and Sample line Volume Report Cut/Fill = 150/980

I believe it has something to do with the calculation method (I was using Average End-Area Method to calculate the materials). When I redo it using the prismoidal method for calculating the materials it no longer gives a negative value for those few fill sections. I just dont know why End-Area method gives negative values for fill in those sections.

[Anonymous]

Also, If I break use the fill areas and lengths between sections to calculate the volume using the average end-area method I get completely different results from what cad is spitting out. But if I do the same using the primoidal method I get the same answer that Cad gives using the prismoidal method. So I think Cad is doing something weird when it tries to use the average end area method.

[neilyj666]

You appear to have samples lines every 100' - the end area method assumes that the ground between sections is linearly varying and if it is not then there will be erroneous values compared to a straightforward surface to surface comparison which accounts for all the irregularities.