in-situ vs. ex-situ Earthwork Calculations 8

[meakai]

Hi,

I am trying to determine the best way to accept a bid for the export of dirt to a landfill site. The contractor used the two borings (6 samples) from the soils report to determine the average weight of the soil. He came up with 1.65 tons per cy. Although I agree with his approach and calculation, I do not feel it offers an accurate representation of the 20,000 cy that need to be exported, and therefore, resulting in an inflated export cost.

I called some trucking/landfill companies and they all figure 1.2 -1.3 tons/cy. The contractor claims that he can only figure in-situ since he would not know what the ex-situ volume would be.

Am I being ripped off? Is there an "industry standard" for calculating dirt "swell"? What is the best (and most fair to both of us) method to calculate a bid for exported soil?

 

[BigH]

There have been several threads in the past on this topic. RKS Services has some good advice (amongst many others) - you might do a search for these. I'd say they were in the last 8 months or so.

 

[Maury]

Actual soil borings and testing of samples are going to be a lot more accurate than somebody else's guess and the in- place density of 122 pounds per cubic foot isn't unreasonable. How is the contractor bidding (lump sum, unit price per cubic yard, unit price per ton)?

 

[cvg]

best way is in-place volumes (cubic yards), calculated by using cross sections of the borrow pit before and after the excavation.

 

[dicksewerrat]

If you have access to a truck scale, go with a unit price per ton. weigh out five to ten trucks with average lods to start with and then if you think the trucks are being overloaded, send ten more through the scale. reserve the right to weigh any truck. You could always call the DOT to weigh and inspect the trucks too.

 

[KRSServices]

Hello All.....I happened by this thread, I hope I'm not too late for a little advice.

Firstly, what is the relationship between the contractor and the the Owner or yourself, in terms of contractual obligation? It wasn't atated, but your thread sort of points in the direction of either a type of open bid or quotation whereby the contract will contemplate a lump sum, or the excavation and disposal is a negotiated item. I noted your phrase of "a fair calculated method to calculate a bid for exported soil". That statement sort of raises a few flags.

The reason I ask is due to the fact that cross sectioning is perfectly acceptable, provided the contractor provides a price with that in mind. If you are pricing by weight, then you will have to either have a calibrated scale affixed to the loader(s) or a site to weigh. Most landfills these days measure their waste stream by weight, so that should not be a problem. Using the DOT scale can cause some problems for the trucker if they are, shall we say, not up on their records and maintenance.

One reason that I am confused is due to the fact that you are concerned about the weight of the material. Is that how it is priced in the contract? From your thread, it appears as though you wil be defining the unit of excavation by truck box count, which I would caution against, because you would be setting yourself up for grief and headaches, particularly if the material profile changes somewhat during the excavation.

A unit rate or lump sum for excavation and disposal would be suggested. In the case of a unit rate, you would then clearly define your measurement and payment clauses for actual units based on either a cross sectioned survey or other method of your choosing. With a lump sum, you will have to be careful to clarify the estimated volume versus actual and have some rationale for payment on overage as well as a defined method of mesuring the "overage".

Hope this helps somewhat.

KRS Services

http://www.krs-services.com

 

[meakai]

Thank you all for your replies. They have all been helpful in one way or another, but after reviewing my problem from every angle, here is the basic problem I am trying to work out:

We have a very small site (22,000 sf) that has an unknown quantity of contaminated soil that needs to be buried on site because hauling to a Class I landfill will be way too expensive. No one really knows how much contaminated soil we will encounter and, therefore, how deep we need to over excavate to be able to bury it below our footing line (we need to maintain a one foot clean soil cap over the contaminated soil).

The site is not big enough to just stock plie the bad dirt and measure it before we start to bury it. So not only do we not know deep the hole should be, but if additional export becomes necessary, what would be the best way to measure the exported soil?

Here's what we came up with:
1) Dig as deep as hole as we can on the clean side of the site (water table and temporary slopes will be the limitations). 2) Start dumping the bad soil in the pit. 3) After we fill up the pit with bad soil, we will survey the footprint of the bad soil still remaining. 4) survey the footprint of the bad soil at 5 foot intravals as we go down to determine the amount (in-situ). Then apply the unit costs for exported material on the in-situ amount.

Hope this all makes sense.

 

[KRSServices]

Holy like to move dirt too much Batman!

While your explanation satisfies your situation, the methodology of the approach to your solution is somewhat confusing. I am assuming the contaminated soil remediation/burial is within the regulatory guidelines, so I'm not going to address that. As I understand, the goal is to have the contaminated soil capped with a foot of clean material below your footing elevation. You do not know how much good material you have onsite and you do not know how much contaminated material to remove. The site is approximately 0.5 acres, so I assume the building footprint is smaller. I also assume the soil contamination is of a hydrocarbon nature...right?

I believe your solution is too cumbersome and costly. How are you proposing to separate the good from the bad? Is someone going to examine each bucketfull of material and test for any contaminants? What happens to the bucket which has some good mixed with some bad as a result of that particular scoop?

You definitely know one quantity...and that is how much clean material is required.

Based on my experience, I feel you are wasting your time and money in moving the material two or three times in jockying it around the site, not including all the effort to survey the material as you described. Propoer compaction is going to be a nightmare with your option. I would propose the wholesale excavation of the material...good or bad...to one foot below the footing. Haul to a landfill. Measure the total excavation and call it a day. Now in the backhaul, import the required good material and compact propoerly.

Hire enough trucks such that there will be no waiting other than minor loading and break issues. 25/30 yard belly dumps or end dumps will work best, but failing that a truck and pup is ok, but takes more time in their respective rotation.

The placement of the clean cap will be the basis for payment. This method will allow the contractor to very quickly move the material once and not waste time in nit-picking, or waiting for the examination of virtually every bucketfull.

Trust me, it's not worth it, your unit rates will reflect the contractor's risk and wait. If you wish further information, feel free to contact me directly.

KRS Services

http://www.krs-services.com

 

[meakai]

You're right on in your understanding of the situation (except that our underground parking garage goes to the property line on all four sides, and yes, we are shoring the whole site as well), and my first inclination was to haul it off and be done with it exactly as you said...that is, until I started getting prices for hauling to a Class I landfill ($90-$130cy). Believe me, I'm with you, I would rather simplify the whole situation.

We have to follow very strict guidelines on the monitoring and testing of soil. That alone will cost about $150k for seven weeks. Even if we decided to bite the bullet and export everything, the dirt will still have to be separated, stockpiled and tested before going out (we have to make sure clean is clean).

No matter what, we also have to over excavate three feet below the deepest footing to put everything on fill to avoid uneven settlement. The one foot cap is the safety cap that allows workmen in the hole to dig and pour footings etc. without HAZWOPER training. So, as you can see, this site is inherently complicated not to mention that we are also required to have archaeologist and paleontologist on site during excavation as well. Can a .05 acre site get any more complicated?

Thanks for your input, I really appreciate it.

 

[DRC1]

I would offer the following suggestions:
1.)For materila to remain onsite, dig a pit, survey the pit, fill the pit with material, resuvey the pit. the difference in volumes is the volume placed less adjustments for shrink and swell. Have a inplace cubic yard price.
2.) If the landfills buy exported material by the ton, have a per ton unit price for material exported to the landfill. Pay off the weigh slips for the landfill. Always buy the comodity in the same units the contractor is buying the comodity.

 

[meakai]

DRC1,
Excellent advice. Thanks.

 

[cvengr]

Keep it simple.

You are paying for soil export to an outside landfill.

Work is force times distance.

The minimum work required is to displace a mass a given distance.

The volume of the dirt in situ is different than the volume of loose soil.

The material being moved may be measured by density (in situ) on site, packed, 1.65 tn/CY might very well equate to 1.2 tn/cy loose in the dump.

Don't fool yourself into believing your volume of in situ soil is the same as loose soil.

Just as his density is going to change, likewise the number of trips he's going to have to haul is going to increase. The mass is remianing the same. He is determining the mass from the specific gravity of the earth. You're fortunate he doesn't calculate it by number of trips. That would favor his estimating and operational costs.

Operationally, earthmoving favors larger pieces of equipment with least number of trips to get the cost per yard as minimal as possible. He will have fixed csts of mobilization, lube truck, dust suppression, and loading.

Least expensive loading is probably a stationary dragline on a crane that lifts by gravity closing its clamshell, a simple pivot at the crane base, elevating to height of the dump truck, then emptying in one traverse. This might be typically referred to as pit run in a quarry,..10 yrs ago about a $1/TN without equipment capitalization or salary.

Compare that to a tractor front-end loader that has to drive up, turn the bucket, lift, back up, 3-point wye turn, drive up to the dump, raise his bucket, pivot and dump, say 3/4 yd, then returns in same fashion. To move the same 8 tn of earth, would cost closer to $4-$16/tn without equipment or salary depending upon the geometry of the quarry/earth source.

Figure you have to move the heavy equipment and the operator along with the product every time it's moved. The higher the ratio of product weight to fully laden equipment weight, the less cost per ton in product transportation costs.

That's why when you run by a quarry and see some old poor guy operating a 50 year old unpainted greasy crane and dragline, slowly pivoting back and forth with a queue of dumps and drivers waiting to be serviced. It's the cheapest way to operatioally deliver the product with low cost capital and least cost operations and very competitive soil availablity.

In Southern Ca desert, Class II Agg base runs about $13/TN on the open market where it is plentiful. Thats for highly angular and fractured gravel and sand with little to no water and little to no clay. Clays will swell and become difficult to compact. River rounded rock, gravel and sand will be easier to break up, by not compact quite as well, but will drain water more quickly.

I usually figure 2.5 tn/cy for initial estimating purposes to procure construction funding. Hauling desnities of about 1.1-1.3 TN/CY. Five yard dumps for general public street access, but 20 yd dump where local authorities allow those loads with low fees. Some states/counties prohibit 20 yd dump traffic during daytime summer month travel or charge exhorbanant impact fees.

 

[meakai]

Thank you very much for such a comprehensive and informative reply.