Grading - Earthwork Calculations (CUT & FILL) 3

[Andres Ayala]

I have been doing some CUT FILL Analysis for some construction sites on my proposed grading plan. I had a question as far as running the approximate CUT FILL Data.

How does everyone account for the rootzone in their calculations? I usually reference the geotechnical report to see if they mention any rootzone on the borings. I have had a couple of projects recently on undeveloped almost dry farm land. The geotechnical reports do not mention any rootzone or I cannot see anything in the borings either.

Do you subtract the rootzone from your subgrade surface or after accounting the final cross section for your proposed grades? What would you assume for a dried up field with undeveloped land? Soils mentioned in the geo are usable for construction, am I to assume all of that will be usable/ need to be accounted for in the earthwork calcs?

Any feedback is appreciated! Hope that made sense.

 

[TigerGuy]

The geotechnical engineer should have included a stripping depth in the report. This is the amount of material that needs to be removed and only placed in landscaped areas.

The area that does not have improvements and the stripping depth will give you a volume of (typically) topsoil, which can only be used in landscape areas (or other areas listed in the geotechnical report).

Then you can calculate the remainder of the cut and fill quantities.

I've investigated sites with stripping depths from 1 inch to 24 inches.

 

[Jrit]

We have had several projects recently where the grading contractor comes back to the client with large charges/change orders for excessive topsoil they had to strip. Sometimes there's a geotech report and sometimes not. Sometimes it's legitimate and sometimes its not, but I'd recommend confirming with the geotech regarding what you should use for topsoil depth.

 

[EireChch]

I would always assume 0.3m to be stripped.

 

[dik]

also, the amount excavated and the amount backfilled, for the same volume, can be different. There may be a difference due to existing native soil volume and the backfill volume.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BigH]

Many times, the zone of topsoil is taken from a surface split spoon - which can be misleading. Always suggest that a number of hand dug shovel holes be made across the whole of the site to determine the thickness of topsoil - the average, and if enough, give the variation from the average. Better to have numbers than just winging it with an estimate especially if large areas are to be stripped.

 

[eea]

In my location, we typically use 4" of topsoil stripping and stockpiling as a pay item in SY in addition to earth excavation and embankment in CY. Essentially we strip off what we place back, so it is a wash and don't detail it in the cross sections. On larger projects with known areas of undercut and deeper topsoil I have shown and calculated the quantities separately as you ask.

 

[Ron]

Agree with BigH....simple, inexpensive process to get a lot of info. A simple post-hole digger plug for 12 inches will tell you pretty much everything you need to know for topsoil stripping. PS....4" is usually not enough...almost never