Need help with cut/fill calculations 4

[holliwr]

Hello:
Can anyone point me to information on the web about how to do cut and fill calculations for grading?

Say I have a 500' by 700' area. I take shots every 25' to form the grid. I would like to know the total cut/fill for the site (not worried about compaction -- yet)

I've checked mainly university engineering sites for info and found a little, but not enough information to calculate what I need.

Thanks,
Richard

 

[MJCE]

You'll need to compute the difference between existing and proposed grades at every grid crossing. Then for each square average the numbers at each corner and multiply the area of the square by the average of the four corners. Typically, positive number are for fill and negative for cut. Write the volume in the middle of the square and then just add up the positive numbers for fill and the negative numbers for cut volumes. Accuracy will depend on the size of the grid. The more grid lines you use the better the accuracy.

 

[BigH]

MJCE is pretty well on. Basically you have developed a contour plan (if you haven't drawn up the grid lines, do it). On the plan, draw in the levels you are interested in - and don't forget to do the slopes. Develop an "finished" project contour plan. Then, it is a matter of using the contours and doing an "original less finish" to determine the volumes (+ for cut, - for fill; or vice versa). Else, use your contour plan to make sections. Draw on your development and calculate by end area methods. We used to use { A1 + A2 + sqrt A1*A2 } in our calcs rather than A1 + A2 all divided by 2.

It is probably amazing how many of the younger members have never worked with plans and sections that they have drawn up given computerization these days.

 

[holliwr]

Thanks to both of you for the reply. I do have one more question though. It concerns the averaging of the corner values for each grid. I have seen one guy who SPLITS the corner values by CUT/FILL. Example: if the grid spacing is 25x25 (625) and one corner is cut and the other 3 are fill, he multiplies the cut corner by 1/4(625) and the average of the other 3 by 3/4(625), then adds these to get CUT/FILL for that grid. Do you do this?? Is it necessary for greater "accuracy"

Also, I currently AVERAGE the elevations to get the proposed new elevation (for road beds, chicken house pads, homes, etc). Is there a better way?

Thanks again,
Richard

 

[jheidt2543]

Here are a few thougths to consider:

1. If you are going to do this kind of work you should really get a copy of "The Building Estimator's Reference Book" by Frank R. Walker Co. It covers all aspects of estimating, but in particular has a detailed outline of earthwork calculations via the Cross Section Method and the End Area Method. There are a lot of other good books out there, but this one covers all aspects of estimating at a resonable price.


2. When doing earthwork cut & fills, you should keep the various operations separate; Clear & Grub (SY), Strip Topsoil (CY), Cut to Subgrade (CY), Fill to Subgrade (CY), Marsh Excavation (CY), Clay Excavation (CY), Unclassified Excavation (CY), Rock Excavation (CY). Then the fill going back in should be separate too in (CY); Granular, Clay, Unclassified, Topsoil, Stone Base etc. All these items are priced separately and it is easier to take them off at the begining. You also have to consider haul-in and haul-out quantities.

3. One of the biggest arguments in earthwork is how many times each yard of dirt gets moved, it is not just the net cut/fill quanitity. If you keep each operation separate, then it is a lot easier to keep track of the movements and costing.

There is nothing wrong with doing these calculations by hand. It is a lot easier by computer, but you learn to understand it a LOT better if you do a few small projects this way, then go to the computer.

Best of luck.

 

[wolfhnd]

Does anyone know the formula for doing it by it's coordinates? Seems like I saw that once years ago. Something like xave2 + yave2 + zave2 / the sum of the values or something like that

 

[MEM1]

You might check out

http://www.ezysurf.com.

It's a contouring program that also does cut and fill. If that doesn't work for you, I have a quattro pro spreadsheet that uses the existing elevations at any grid interval and the proposed elevations based on percent slope to calculate cut and fill. It uses the same method mentioned in this post, but also allows you to put in a compaction factor %. Shoot me an email if you are interested.

smurrison@cox.net

Scott Murrison

 

[DRC1]

To answer holliwr question; you want to know the total amount of cut and the total amount of fill because you have to excavate the total amount of cut, not the net so you want your cost based on the total cut vs. the total fill. Also you will get some shrinkage of the cut material when it is placed so the net will not be the best way to do it. As far as accuracy goes, not matter how presice yor take off and calculations are, your model in general will probably be within 10 % +/-. I would use the actual elevations at the grid points instead of an average, unless you feel the pads and roads will be built to a singlke elevation (If you do, make a note in your calculations so you can rember later what you did). Jheidt2543 has some good comments. Trying to break out the types of cuts and fills later is a pain. Most sites require all the topsoil be stripped, if so reduce your elevations by 3 to 6 inches. It will probably make difference. It really isn't complicated, but it is worth spending a little time thinking about what you want to accomplish before you start so you get the numbers you want at the end.

 

[bobbert]

What is your general site topography? 1' of elevation change or 5'.

Average end area calculations between sections is the best method for hand calculations. The number of sections depends on the topography. Compaction must be considered for the final design.

In short, average end area(s) is the best method for use by hand calcs.

I am in Houston Texas, we have flat topography, and at times move 100,000 to 1,000,000 yards of the Earth.

 

[holliwr]

Hello again. There seems to be some confusion wit my first post so let me clarify some points.

When I level a pad, for example, I first clear the trees with the Cat. Then, I take shots at 25' intervals for the whole pad area. I then put these on the corners of a grid and average all the shots to get the "proposed" elevation. Then I figure the cut/fill for each grid section by adding all the cut and all the fill for that section and multiplying those by the corresponding grid area (25x25=625). If 3 of the corner points are cut, then I average those and multiply that by (3/4 x 625 = 468.75) to get the overall fut for that grid. Then, do the same for fill. Then I add all the cut and all the fill to get the totals. Then I divide total cut by total fill to get a percentage. Hopefully, that percentage is about 1.2%.

I know this is NOT the full technical method. It does not consider slope, compaction, etc. But, will it suffice for my simple operation?

Thanks again,
Richard Hollingsworth

 

[jheidt2543]

Holliwr,

That is the cross-section method in a nut shell, but I don't know why you really need the % cut to fill. If you are allowed to use the cut material for fill, all you really care about is how many yards of fill you need (using a suitable compaction factor) and how many yards of borrow or haul-in.

Using a 25' grid should provide pretty accurate quantities. Most of the small construction sites I did cut/fill calcs for I used 50' or 100' grids depending on overall elevation changes across the site. And, of course, you can use different grid sizes for different areas of the site too.

 

[vicman2]

Average end areas is the method you want to use for hand calcs.
1.) It is easily explained to contractors and clients.
2.) It is commonly used throughout the construction industry and can be defended in a dispute. Try explaining some engineering software to a judge or jury.

You might want to plot your end areas to scale on graph paper-this will allow a better visualization of cut/fill.
Counting squares of the grid would give you check in your calcs. To bring this idea into the 21st century you could create a grid in Autocad and use Autocad to calc areas. I believe that you would need extra stations at the transition point between cut/fill. You will need to know the expansion factor of the material you are excavating etc.
We used this method for 40 miles of railway grade in the early '70s and only had real problems with placed material.

 

[jheidt2543]

vicman,

I agree that the Average End Area Method (AEAM) is also a good method for earthwork calculations, particularly if you plot out the sections. An earthwork company I know of wrote their own program 25 years ago and used the AEAM method and the program plotted each section as a viusal check. However, my sense of it is that, most earthwork for building construction is done by the Cross Section Method (CSM)and most highway/railway dirt is calculated by AEAM.

I learnd both methods at the beginning of my career and have used both, but CSM seemed to fit the projects I worked on the best. But, the best method is the method you understand and feel most confident in. As I said earlier, doing the take-off by hand teaches you a lot and when you "graduate" to the computer you have an understanding of what the computer is doing. When we finally computerized, there wasn't a happier guy. I use to hate sitting up until 2:00 AM doing take-off extensions!

 

[DRC1]

Your proposed method should work. As a few of us mentioned before, if yo are going to strip all the topsoil before bringing on fill, it is a good idea to keep that seperate. You probably also should calculate the total cut and total fill then calculate the net after making adjustments for shrink & swell. It isn't that much more work and if you later want to to know the total cut or fill, you won't have to recompute.
Good Luck

 

[monique69]

following holliwr question, what formula or calculations would you suggest best to use and likewise almost accurate when estimating cut and fill with a volume of about 15,000 cum and 5000 cum respectively or say for hectares of land to be developed. thank you for any help you may suggest. i will appreciate it, really...