Step by Step Process for calculating Earthwork? 1

[simonrr]

Hey fellas,

I would like to know if someone could shed some light on a step by step process for calculating earthwork. I have access to the Autocad Civil Design package and know how to calculate the fill/cut using the program but I am unsure how to take into consideration the stripping of topsoil, clearing, cut/fill to subgrade, clay/rock/unclassified excavation, etc. Thoughts?

Thanks.

 

[jheidt2543]

Do a "Keyword Search" for "earthwork calculations" and you should find some past threads with information that should help you. Here's one to start with: thread158-36736

 

[SteveWarfle]

On a typical site, the topsoil is removed first and stockpiled for placement later. Figuring the depth and volme of stripping is the first step. Forgetting to factor this leads to erroneous calculations. Here's why: if you are in a cut area, the stripping removed doesn't add to the amount of material, it just costs more because the operation will be in two stages.

But in Fill areas, if you first remove material, and in essense lower the existing grade, the amount of fill required to bring the site up to grade will require additional material to replace what was stripped.

The next thing to factor in is the thickness of the materials used for paving, building pads, etc. These thicknesses need to be subtracted from the proposed elevations.

And if topsoil replacement is required, adjust the proposed grades so the C & F is figured to the bottom of the minumum required topsoil. The reason you need to do this is the reverse of stripping. If there is a fill required from the bottom of stripping, you will place fill to the minimum topsoil replacement requirement, and then place the topsoil. Depending on the amount and value of topsoil, the fill, since it is non-load bearing in a topsoil area, may be the same thing. But keep in mind that in a cut area, you have to over-excavate to leave room for the material. This increases the amount of work significantly, and is often overlooked in the budgeting stages.

Now, when you are figuring the Cut & Fill, keep the amounts of fill seperate for each area...that way you can keep the structural requirements (under paving, builings, etc.) seperate from the non structural requirements.

That sums up the basics. Here are just a few of the factors that affect the overall numbers:

Soil borings. these will determine what material is yielded during excavation. If you could break down the amount of fill by strata, and compare it to the fill requirements, you can determine the site balance. Too many site are designed with the assumption that stripping and cut compared to fill determines the site balance, with no regard to fill requirements.

Shrinkage: Material in its natural state is rarely at the compaction levels acieved during the process of cut & fill. If material on a "balanced" 100,000 yard job shrinks 10 percent when re-placed on a site, and the site was balanced with no consideration of shrinkage, the site will be 10,000 yards short. Here is a more picturesque explanation:

http://www.insitesoftware.com/091999.htm

Over-Excavation: Sometimes a structure (ex. Building) will require over-excvation of material below it, either to an amount (ex. 3 feet of fill required below pad) or to a specific strata (material to be removed to bedrock). In these cases, be usre to calculate the excavation and backfill requirements fro these special circumstances.

Anyway, that is a lot of things to think about, but it can be done with a lot of time. The company I work for publishes software to accomplish this task easily. The problem with most design oriented software is that it is difficult to account for multiple surfaces. But it can be done. Just stay organized.

Good Luck
Steve Warfle
Product Manager
InSite Software Inc.

http://WWW.INSITESOFTWARE.COM