Saturday, 12 October 2013

Not your Average Volume Calcs.

In some customised training recently I had a question on calculating the volume of material that was dumped on the side of an existing road. It turned out to be less straight forward than initially expected. The existing road is higher than the ground around it and original had a 2:1 embankment - that is all the information provided on the original condition. The fill material was dumped on top of this embankment. No survey existed for the original embankment so we had to somehow recreate the original ground level before we could calculate the volume of dumped material.

Belo is a screen shot of the current situation with a section through the fill to be quantified:
Manually drawn on one section below is the volume we need to calculate:
What we need to do is recreate the original field levels and road embankment at 1:1 to do our volume calculations - for simplicity we are going to assume the slope of the field continues in at the same grade towards the road:
In plan below you can see the toe of current embankment - blue line. Red line is the road edge. 
To recreate the original field slope where the material was dumped we are going to use the overlaywidenmatchslope subassembly to build a corridor and get it to look at the existing field slope and continue this back in towards the road. Insertion point is toe of current slope and setting a target (green line) further out in the field will enable the assembly to calculate the slope of the field. 
The resulting corridor surface is shown below in purple. (actual slope may have been different but it is a good estimate). 
Next build another corridor with a linkslopetosurface subassembly. Alignment is existing road edge and existing profile. We will target the surface from the first corridor. 
The resulting corridor surface is shown below. We now have a good estimate of what the original ground levels were like before the material was dumped. 
Next to calculate the volumes we can define a material bounded by the three surfaces. 
 Volumes report below. 

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