Thursday, February 16, 2012

How to Rapidly Build a Staged Earthwork Filling Curve with Civil 3D

Sometimes you have an existing ground surface and a final design surface, and you want to know what will be the earthwork quantities at different stages of completion. This is sometimes called a filling curve, and usually the stages are at level elevation increments (though this method doesn't require them to be).

Let's define our terms first:

1. Se is the existing (initial) surface
2. Sf is the finished (final) surface
3. Ss is the staged surface under which we want the stage/phase volume.
4. Volume of a surface over another surface is the fill only. We are not interested in the cut volume, and we don't want to subtract it.

Now let's set up our model:

1. Create surface Ss to have the exact same areal extent as the daylight line of where Sf meets Se. Surface Ss cannot be any smaller or larger or varying in extent from that daylight line.

2. Build surface Ss to a level elevation or to any slope and terrain desired.

Now let's calculate the curve:

1. For every desired point on your filling curve, adjust surface Ss to the desired elevation

2. At the desired elevation, calculate the volume of Sf between Se and Ss as the following difference:

Stage volume above Se and below both Sf and Ss (stage fill; blue area above)
= (equals)
Volume (fill only) of Ss over Se (Ss fill over existing; orange area above)
- (minus)
Volume (fill only) of Ss over Sf (Ss fill over final; green area above)

By defining a stage surface whose extents match exactly the daylight line of a proposed surface compared to an existing surface, we can calculate the volume at any stage elevation as the volume of the staged surface over the existing surface minus the volume of the staged surface over the finished surface.

No comments: