Earthwork, CUT FILL revisions 2

[engcap123]

From my existing and proposed contours and spot grades I'm able to get cut and fill values through AutoCAD. Once I get those I need to make revisions to account for building and parking pads and topsoil, etc.

I realize how to revise the numbers for building and parking pads but am confused with topsoil.

Roughly 6" of topsoil over site will be stripped. Should I count this as cut over the whole site? What about areas of cut already taken into account through AutoCAD and building and parking pads?

Any help on how to revise AutoCAD cut and fill values to account for all other issues, mainly topsoil, would be greatly appreciated.

Is there a way to use AutoCAD to incorporate building and parking pads and topsoil into the cut fill calculations?

 

[queque]

Can you provide a simple example of how you use AutoCad to calculate cut and fill?

We have AutoCad but need to understand what extensions are required to calculate cut and fill.

 

[cvg]

top soil will likely be stripped during the clear/grub activities as first order of work. Therefore, you may want to adjust your existing contours by 6 inches to account for this.

 

[sewerdesigner]

If you are using Land Desktop, you can simply raise/lower your surface by a set amount. You'll get a fairly accurate number on large sites, but on small sites you have to be careful around the edges and determine if it impacts your calculations.

 

[sewerdesigner]

Also.. In addition to what I said earlier, it is very important to state your assumptions. If you remove 6" of topsoil, state that in your final results. You are on the right track, just remember it is important that contractors can read and understand your results.

 

[bltseattle]

I would not take any time to adjust the contours, I would enclose the area overexcavated for topsoil with a polygon and use the measured area to make a manual calculation. Fast & easy. This way you don't count buildings, parking lots, etc. A landscape plan may show the limits of topsoil installation and you could possibly use the polygons already in the file.

 

[digger95]

I have use AutoCad, and Land Development Desktop for cut/fill calcs. Initally I adjust my create an ex-topsoil layer by adjusting by the topsoil thickness and then create a subgrade layer by subtracting off the bldg pad thickness, parking lot thickness, and the topsoil respread thickness to calculate my cut/fill. I then account for my utility spoil and footing spoil by manual calcs. One thing to remember... dont forget to include the shrink/swell. In Chicago we have had good luck with 0%/15%.

 

[nohd]

I think you are using Land Desktop ACAD that can run cut/fill cals,..here CA we have these program too Carlson take-off (CADD as well) but speaking of calcs of cut/fill we used AGTEK. Anyway i think you need to strip the upper 6 inch topsoil before you run the calcs.. let me ask you, is it import/export job?

 

[RCEJD]

Our firm uses, as the other posts have mentioned, use LDD thru Autodesk, using Autocadd as the run engine.

As a guide lines in our calculations, we evaluate the areas to be disturbed by grading, and use that as our area of stripping. We then convert this value into a volume, whetehr the soils report recommends 4, 6, 8 or 12 inches for stripping.

We then run the earthwork volumes for the site. In these programs, considerable error can occur on the boundaries depending on the extent of the topo coverage. The programs convert the topo into TINS as part fo the 3d model. You also have to use break lines to accomodate walls, curbs, etc. The programs allow you to use the composite, pyramid or grid methods for the earhtwork calcs depending on the type of calculations.

Based on the soils report recommendations recommendation for bulking or shrinking, the programs will allow you to assign various values to different depths. This is one are of considerable error. For instance, you may have 20 percent shrinkage in alluvium in the upper 10 feet, but at a depth of 20 to 30 feet, this value may decrease to 5 percent. The programs allow you to assign different values for different depths.

Good luck.

 

[francesca]

When we calculate our subdivision earthworks, we start by measuring our disturbed area. We multiply the area by the depth of topsoil (12" in our area) to calculate a topsoil volume.

Next, we assume that the contractor will replace 6" of topsoil over the site area that is not covered by roads. To get this area, take your original disturbed area and remove the total road area (length x width from back of curb to back of curb).

You will now have a waste topsoil volume, and a replacement topsoil volume.

The next step is we generate a "DTM-STRIPPED" layer in Terramodel, by copying the DTM of only the disturbed area to the new layer and subtracting the depth of the topsoil from the entire layer. This is the "stripped" surface DTM.

To generate our "PROPOSED-DTM" layer, we start by tying our proposed contours into our existing contours and generating points off the contours. This is a quick-and-dirty method, but it's better than just taking proposed contours without tying them into the existing contours. For more accuracy, add your road points, as this will include high points and low points on your roads and will make a denser DTM.

When calculating the cut and fill volume, remember to include expansion/contraction factors. We assume that cut dirt reduces by 15% when compacted in fill, and use factors of 1.00 (cut) and 1.15 (fill) in our Terramodel volume calculation.

We get our cut-and-fill volumes from the "DTM-STRIPPED" and "PROPOSED-DTM" layers, inside the boundary of our disturbed area.

Remember that the proposed DTM includes the 6" of replaced topsoil and also the other materials in the road pavement. To account for this, we subtract the replaced topsoil volume from the fill volume and also subtract the volume of road materials by taking the depth of pavement and multiplying it by the road area.

If your road pavement is shallow, like in our subdivision roads (8"), then you can simplify your calculations by just assuming that 6" of topsoil will be replaced over the entire disturbed area. The error of 2" over the road area will be much smaller than the errors inherant in the cut and fill expansion/contraction factors and the topsoil depth assumptions.