Volume calculations

[Old Jim]

Hi.

I don't do any civil desing work ever. But I find myself in a position where I have to figure out cut and fill quantities for some roads. All I have is an original ground surface built, road centrelines and proposed final grade spot elevations.

Could someone give me a brief explanation of the steps involved in doing this. In my experience the manuals don't seem to be very helpful unless you have an overview of what you must do.

Thanks Jim

[MHultgren]

You will need to create your FG surface from the points and any additional breaklines (for your curb cuts and subgrade), Then you will need to define your site and process your volumes using the two surfaces. I usually run all three to help find bad spots in the surface. When your Sections are over 25% off from the Grid and Composite volumes, it usually means there is a bust in one of the two surfaces somewhere. I have also seen where the composite is way off from the grid as well. When this happens, I create the TIN or 3D PolyGrid and do a View from an angle to find where the bad spot(s) are. It is usually easy to find them as you will see a "Spike" in the tin. Find that point or object and edit the elevation, then rebuild your surface and try it again to see if you got it cleaned up.
Added... Don't forget to edit the Datum for your points if they are FG and you want to remove the Pavement and Subgrade thicknesses.

[coronadog]

Attached is a word document I created to in an instructional session on how to create surfaces, and do cut and fill analysis. Hope it helps.

[melanie.santer]

Hi.

I don't do any civil desing work ever. But I find myself in a position where I have to figure out cut and fill quantities for some roads. All I have is an original ground surface built, road centrelines and proposed final grade spot elevations.

Could someone give me a brief explanation of the steps involved in doing this. In my experience the manuals don't seem to be very helpful unless you have an overview of what you must do.

Thanks Jim

Hi:

In order to create a volume surface with your earthwork quantities in it you must go through three steps in this order

1. Terrain--> Select Current Stratum. While doing this you select your surface 1 as your base and your surface two is always your comparison surface.

2. Terrain--> Site Definition--> Define site. You are drawing a rectangle around the area that you want volume calculations for. Your grid M and grid N size is dependant on how accurate you want our volume surface to be, the smaller the value, the more accurate the volume surface but be sure not to have a very large site and put a very small number for your grid, you could potentially lock up your system this way.

3. Terrain-->Grid Volumes-->Calculate total site volume (this is the less accurate method, but it is the only method that allows you to create grid ticks) or
Terrain-->Composite Volumes-->Calculate total site volume

Remember when naming your volume surface NOT to use a name of an existing surface in your drawing, it will overwrite that surface without prompting you if you do this.

Hope this helps!