Strippings Depth (Waste Soils)
Strippings Depth (Waste Soils)
(OP)
Hi,
I was hoping for some advice concerning a project that I am working on that is currently under construction. I realize that earthwork calculations are somewhat of a best guess, and that strippings depths vary greatly from site to site / region to region.
The problem that I am having on this project (heavily wooded site) is that we do not have enough dirt to do the fill proposed by the plans. My calculations were based on the assumption that there would be 9" of strippings required; The grading contractor has stripped the site to a depth of 1.5' (300 acre subdivision), which of course creates a big problem. We have more strippings to waste than anticipated; and we have more fill, and less cut to do it with. The client did not allow us to get soil borings due to time constraints.
My questions are:
Does 1.5' of strippings sound reasonable? We have a similar site in the same area where the soil borings reported that the top soil depth was 4".
What effect does the fact that the site is heavily wooded have on the strippings depths?
Are there seasonal factors involved that I should be aware of? The majority of the earthwork was done in the Winter which tends to be wet around here; however the the site slopes at 10% or more, so it is well drained.
How can I prevent this problem from happening in the future?
Thanks alot for any input.
I was hoping for some advice concerning a project that I am working on that is currently under construction. I realize that earthwork calculations are somewhat of a best guess, and that strippings depths vary greatly from site to site / region to region.
The problem that I am having on this project (heavily wooded site) is that we do not have enough dirt to do the fill proposed by the plans. My calculations were based on the assumption that there would be 9" of strippings required; The grading contractor has stripped the site to a depth of 1.5' (300 acre subdivision), which of course creates a big problem. We have more strippings to waste than anticipated; and we have more fill, and less cut to do it with. The client did not allow us to get soil borings due to time constraints.
My questions are:
Does 1.5' of strippings sound reasonable? We have a similar site in the same area where the soil borings reported that the top soil depth was 4".
What effect does the fact that the site is heavily wooded have on the strippings depths?
Are there seasonal factors involved that I should be aware of? The majority of the earthwork was done in the Winter which tends to be wet around here; however the the site slopes at 10% or more, so it is well drained.
How can I prevent this problem from happening in the future?
Thanks alot for any input.





RE: Strippings Depth (Waste Soils)
But, there is some serious questions to ask. You have indicated that the client did not permit soil borings due to time constraints and yet he was risking a 300 acre development?
1. Most good local geotechs could have given you preliminary information within a day or two of the finish of the borings or test pits. This would have been reasonable AND better than no information at all.
2. Where were your firm (or the client) when the contractor was stripping? Anyone on site? . . . or did the contractor just go on 'is merry way. See my last comment above on the type of contractor's equipment. If he caused extra stripping to occur, then this should be on his account - both for the stripping and for the filling required. If you weren't there (or no compentent person looking after the owner's interests were there), then, well, how can you tell if the "large" stripping was a result of the ground conditions or contractor's methodology/equipment.
Some advice from an old man (besides being Big) - as to how to prevent this in the future: Stripping is ALWAYS a contentious issue. In development work, you need to be quite careful (one reason I have never liked it). So, borings or no borings, you should go dig a few hand dug test pits to determine the thickness of topsoil and or unsuitable material so you don't get burned. If you have borings, it was our company policy not to use the "spoon" representation of the thickness of the topsoil but to actually dig three shallow holes near by and measure in situ - directly. I think this is some good advice. On 300 acres, assuming a per inch basis for cost and, say $5/yd3 for unit rate (for example), even one inch would be a volume of 40k yd3 or, say, a cost of $200k. Wow!! . . . and spending a couple of grand on a quick and dirty geo investigation . . . So, your 9 additional inches of excavation over and above your 9 original inches means nearly $1.8 million! and this doesn't include the imported fill to raise the grade back up 9 inches.
RE: Strippings Depth (Waste Soils)
1. I wouldn't call earthwork calcs a "best guess", but they are more art than science and rely a good deal on local knowledge. Also, once you get those big machines on site, they seem to keep moving! Look at the difference 1" of thickness makes on a large site in BigH's comments. Topsoil isn't consistant over an entire site and neither is the first cut of a scrapper exactly 4".
2. Most of the good dirt contractors I've worked with have their own drill rigs to check a site or at least dig a few pits to check not only topsoil, but the thickness of various layers. This is important, particularly on a big site, even if there are soil borings by a geotech. They need to figure out where stock piles of different materials are going to be placed. (Really! The good contractors actually have a plan!)
3. It seems some owner's set up a job for problems. How can anyone go into a 300 acre job without soil borings? Yes, we all want the job, but sometimes you have to tell the owner he is full of XXXX, that's what he is paying an engineer for.
RE: Strippings Depth (Waste Soils)
I will keep all of these things in mind in the future; thanks again.
RE: Strippings Depth (Waste Soils)
RE: Strippings Depth (Waste Soils)
Thickness of organic laden "topsoil" varies from zero in the deserts of Nevada and Arizona to 7-8 feet in valley bottoms of Missouri and Iowa.
RE: Strippings Depth (Waste Soils)
RE: Strippings Depth (Waste Soils)
RE: Strippings Depth (Waste Soils)
p.s. You know what assume means, I presume? ass u me .
RE: Strippings Depth (Waste Soils)
RE: Strippings Depth (Waste Soils)
"Well, Rookie2, we undercut the site, then overfilled it, but don't wory, we got it right the third try. We just need $45 million for all the extra work we did."
RE: Strippings Depth (Waste Soils)
RE: Strippings Depth (Waste Soils)
I should also mention that the developer is a semi-retired civil engineer whom I have alot of respect for. I'm sure there's some wisdom in there somewhere.
RE: Strippings Depth (Waste Soils)
You're right, "assume" was a poor choice of words. But 6" of strippings is the local standard benchmark. It's rarely more than 9" or less than 3", and since it's usually fairly easy to incorporate it into fills it really doesn't matter unless we're on a flat site with minimal cuts and fills - no place to put it and bridge over.
RE: Strippings Depth (Waste Soils)
The most important point is that the depth of stripping wasn't accurately known and the stripping guy used inappropriate equipment/methodology causing an overrun as a result of his action - how can you then 'ding' him and for how much? There is little to no basis for the extra costs deduction.
RE: Strippings Depth (Waste Soils)
Dozerman you mentioned that you worked in Central NC; I work in the Charlotte area. We DO assume strippings (usually 6"-8"depths), even when we have soils reports (usually 4"-6"). The reason is, we have no idea what the guy driving the equipment is going to decide is a reasonable strippings depth. I have no doubt that he has never seen the soils report; Usually I wonder If he has even seen the plans.
Even if he has, very likely he is going to err on the conservative side so he doesn't have trouble with proof rolls, density tests etc.
I work for a small site development firm (9 people). We don't have the resources to be on site daily to inspect construction. When we have offered this, the developers are not willing to pay for our time. Sometimes they pay us to be involved with the contract preparation, sometimes not.
When I asked how do I prevent this problem (strippings) from happening in the future; I should have asked how do I prevent It from being my fault in the future.
I realize I will probably get some negative responses; but I'm just trying to learn.
RE: Strippings Depth (Waste Soils)
RE: Strippings Depth (Waste Soils)
I used to work in the Geotech dept of a multi-disp. firm in Richmond VA. I also did a lot of construction admin for them. As you said, the reports will typically tell you 4-6", we usually said 6-9". We had the same situation develop in heavily wooded areas, where the final depth is 18", so when I read your initial post; I knew exactly what was going on.
From my experience in the area: Your spec likely says to remove / strip the organic material form the site. With the trees you have there in the heavily wooded areas, the roots tend to be wide spread, and much of them are in the 12-16” range. When they cleared, they likely just went through and pushed them over, leaving holes some of which can be 2 feet deep (even if they cut them for the lumber, they still normally pull the stumps). They will lightly grade the site as they go to avoid having all those holes, and thus mix the topsoil a bit. This will increase the total to be stripped, but needs to be done to some degree. Even if the roots were left in the ground, as they come through with scrapers, they will expose so much wood that no inspector would tell them to leave it.
So, what can you do?
1. Make it clear, in writing, to your client that you cannot accurately tell the depth of topsoil without geotech information of some sort.
2. Make it clear, in writing, to your client that you cannot be responsible to verify quantities for unit rate bids if you are not there, and that cannot be responsible for contractor overages unless you have the ability to see the differing site conditions and be able to act in a timely fashion.
3. Make sure your spec is clear as to what you want the contractor to clear/strip. Method is up to them, but have a definable goal that could be followed by a field inspector. Indicate you should be contacted if conditions differ, the contractor does not get paid for over excavation, and they are responsible for achieving the design grades.
4. Be sure all know geotech data is disclosed to bidders, but that they know it is informational only, and not contractual. They should have the right to inspect / dig on the site as well.
5. Revise your bids to be lump sum (if your spec is clear what they are to do). This way, the general will watch the clearing / stripping guys to avoid having to do more work. The inspector needs to be sure the spec is followed, and the work is done properly.
My original post was in reference to things you had said about how your current situation came about; however, your contractor will burn you every time (when they need / want to) if your specifications leave them room to that.
So, after all the details, the summary: Define your scope. Define your limitations. Define contractor’s scope. Define how they get paid.
RE: Strippings Depth (Waste Soils)