Excavation and Replacement of Non-Engineered Fill - Contract Question 8

[Blairsy]

I practice in an area where there a few native sites being developed. Most sites are covered with a decent thickness of non-engineered fill ranging from practically trash to soils that require an experienced eye to discern whether it is made ground or not. Since such materials are "undocumented" unless available records indicate otherwise, we require complete removal (over-excavation and replacement) within the influence zone under footings and slabs. This is of course when shallow foundations are specified and the cost to remove the fill is more economic than deep foundations or in-situ ground improvement. Regardless of the number of borings or tests pits that have been done during the site investigation phase (and logs included in the bid documents), the company I work for elects to bid such projects as lump sum unless the client requires otherwise. This requires the contractor to inherit more risk and interpret the subsurface data to estimate a volume of artificial fill to base his bid. I'm just curious to know what people's thoughts on this are and if there are better ways of doing it. I've had a few instances now where contractors don't seem to realize that the undocumented fill had to be removed, even though it states it in the bid drawings and specifications. Most of these projects are for public clients who are required by law to accept the lowest bid.

 

[GeoEnvGuy]

Lump sum bids to include unknown quantities, I guess the winner is the one who estimates the least amount of fill to replace. If I were bidding I could say I assume zero as my total and anything above that is subject to a change order. My price is the lowest but my change order is the highest. If you are not interested in change orders the contractor can go bankrupt, walk away or put a lean on the project.

You are better off to get the engineer to give you the best estimate and a high estimate for quantity and assume the difference as a contingency. Get bids on the best estimate and require a unit rate for estimated quantities and inform any amount over the estimated quantities is at the same unit rate.

As a general comment larger earthworks should never be bid lump sum. There should be a drawing to show existing, foundation prep, and final, subtract these surfaces and get volumes for bidding. The contractor should go out survey for as-built and do the same subtraction for actual quantities for pay. The contractor surveys should be passed onto the engineer to determine if they are within tolerances and if the design intent is being met.

Edit: Also foundation should be approved by an engineer before placing engineered fill on top.

 

[MTNClimber]

You are better off to get the engineer to give you the best estimate and a high estimate for quantity and assume the difference as a contingency. Get bids on the best estimate and require a unit rate for estimated quantities and inform any amount over the estimated quantities is at the same unit rate.

This. Talk to the owner and let them know of this issue. This can make or break a contractors bid or even the owner's purse. It is in the owner's best interest to have everyone bidding on the same work.

 

[Blairsy]

Is it not understood that since the terms are lump sum, and no unit price is provided for over-excavation, that the contractor should be making his own estimate based on the boring and test pit logs (which show undocumented fill depths and elevations at those locations) and including that in his bid? If 10 out 10 borings show fill to depths between 3 to 5 feet below foundation bearing elevations in a building footprint, I don’t see how he could assume 0 to win the project (lowest bidder wins here)and then justify a change order to make it up. The presence of the fill below the bearing elevations would not be “unforeseen” so to speak. He has all the subsurface data the engineer has, and the difference in his estimate vs. the engineer’s estimate would fall back on interpretation of the subsurface data. Forgive me if I am being naive; I don’t have much experience in the non-technical areas of engineering.

 

[GeoEnvGuy]

It's not a contractors job to interpret test hole results, that's an engineers job. It is his job to follow specifications and drawings. If he finds unexpected conditions he should stop and inform the engineer and ask for more specifications and drawings or if this is to be expected.

In terms of claiming "unforeseen", if 10 of 10 holes show 3 to 5 feet of fill to remove. Unless those are the only 10 spots I have to dig a 6 inch hole, I assume less in every other area and change order as there was no hole in every other area to inform me.

If one contractor assumes 4 as average and another assumes worst case 5 ft who wins. So they all bid the minimum 3 and change order for unforeseen circumstances everywhere there was no drill hole to show more than 3 ft.

In tendering you are better off to state the contractor is to assume 4 feet for the purposes of bidding but investigation shows it can range from 3 to 5. No additional compensation will be provided unless contractor can show more than 5 ft over the entire site.

By doing this the owner wants the price of 4 but the contractor can win at 3, lose at 5 and change order for more than 5. This splits some risk and says we don't want you to lose your shirt if it's more than the investigation findings.

 

[Ron]

Why do you automatically assume fill is bad? That's what a site characterization is for. It is wasteful to overexcavate and backfill when a little more investigation would better define the near surface soils. Observation pits are not great for determining the relative compaction of a site. Manual auger borings will give you a good idea of the relative compaction of the near surface soils. Couple that with observation pits and you can do a good characterization of the near surface soils and save your client a lot of lost time and money.

 

[Blairsy]

GeoEnvGuy, I agree with you. If the engineer drills 10 borings in the footprint of a proposed building and unsuitable bearing soils requiring overexcavation are encountered in each boring to variable dpeths, in my opinion it should not be the contractors responsibility to interpret the subsurface data provided in the contract documents and interpolate between exploration locations. So lump sum terms for this work is not appropriate and a court could potentially rule in favor of contractor due to the ambiguity. That is my opinion anyways. Are you aware of any references (case histories, federal guidelines, etc.) that would support this opinion? The company I work for is just so damn hell bent on reducing geotechnical liability and risk that it seems like is could end up biting them in the a**.

 

[oldestguy]

A word of advice here. Do a check of the posts made by member "Ron". A great deal of experience is possessed by that member and I'd go by his advice 100% of the time ahead of all others.

 

[Blairsy]

I appreciate everyone’s advice and 100% agree with Ron. I have seen a few cases where the fill has been there for so long and is denser than the actual native soils beneath it. But the position many engineers I know take is that you cannot explore every square foot of a site, and if you know there is artificial fill, there is always that small chance there could be a buried trash pocket within it that you obviously don’t want under a building. But then again, there is always a small chance that native deposits can contain pockets or seams of low strength material you wouldn’t want under a building either. Please keep in mind I am a young engineer, and many of these decisions are out of my hands. However I am beginning to form my own opinions now and express them rather than simply listen to older, more experienced engineers I work with. Two years ago I would not have created this post.

I am trying to look out for our clients. Projects bid lump sum that require overexcavtion of unsuitable material beneath structures, and that don’t have at least a base bid amount/volume that all the contractors have to at least include in their bids seems unfair to me. And if crap were to ever hit the fan and a contractor were to issue a claim making the argument that it is not his responsiblity to interpret subsurface data to make an estimate of an essentially unknown/variable quantity, I’m not so sure the owner would prevail. When engineers and contractors work together, projects are successful. When one of them throw another under the bus in an attempt reduce their risk to near zero, everyone involved suffers.

I want to be able to go to my boss and say “hey, this isn’t right. We could be putting our clients at risk by expecting the contractor to interpret subsurface conditions to such an extent.” I’ve been trying to find a case history or some legal precedent that could back me up. But no luck so far. All of your input has been great though, and I thank you.

 

[Ron]

OG...that's very kind and I'm certainly honored to have you, with all your experience and knowledge to say that. Thank you.

Blairsy....I typically handle quantities that may vary by putting a base allowance in the plans/specifications, then requiring unit rates for all work at the time of bidding. That way all contractors bid with a captive allowance and the only unknown is the ultimate quantity, which may be higher or lower than the allowance. If the whole allowance is not used, then it goes back to the client through a negative change order. If more is required, you have the unit rate to keep the contractor honest in his/her pricing. I've used this process for years and it works well. One of my clients just got a $26k negative change order on a $1.5 million job for a partially used allowance.

 

[Blairsy]

Ron - That certainly seems like a good and fair approach for all parties and I would prefer to see more projects I work on done that way. One question though; how do you go about verifying the quanities/volumes that are actually dealt with during construction? For overexcavation or rock excavation for example, would you require the contractor to survey the subgrade resulting from that work and provide you with the survey information so you can do your own review? Or do you require someone on-site full time during that work to document it?

 

[Ron]

For earthwork, having someone independent from the contractor there for determining haul volumes is better. Before and after topographic surveys are helpful, but again, should be done by a licensed surveyor, not the contractor's staff.

 

[theCorkster]

Someone purchased this site and either did or did not know about the fill and what impact that fill would have on development.

Regardless of whether they knew or not, it is their site. They own it. And they need to address the fill issue to the satisfaction of the design team (geotechnical and structural engineer) performance requirements.

The contractor should not be held responsible for truly unforeseen conditions (e.g. the fill deepens to 8 feet in pockets).

Establish a depth and request an add price per cubic yard for over-excavation/reconstruction below that depth.

This solves bid issues for comparison purposes.

Your client should appreciate this approach since it resolves the issue and keeps equipment moving and doesn't dump the owner's problems on the contractor. Does anyone lose?

With regards to allowing fill to remain in place in it's existing condition - explain the potential issues to the owner and let them decide if they want to assume risks associated with leaving it in place. If they decide to leave it in place they will receive the benefit of a lower construction cost that they should set aside to address post-construction issues associated with fill non-performance (like this will happen). Good career public work personnel are not likely to go down a road that will require them to explain later why they allowed a course of events to occur that will detrimentally impact their career or require more government funds to remedy a real problem.

 

[fattdad]

Some engineer could have already determined the thickness of an engineered subbase to be placed below all foundation elements to mitigate settlement. If the existing fill has variable modulus (it will), then all that's needed is to make an interval of predicable modulus below the footing. Maybe like 4 ft of stone (modulus of 400 tsf)? You'd have to do the elastic solution to know the seat of settlement and to what extent you needed subbase engineering.

Then it's a matter of getting the overall subgrade suited for slab-on-grade construction. Is it a heavily-loaded industrial floor slab (1ksf)? Is it for office space (0.125ksf)? For the former, you may need more than an engineered subbase below the footing. For the latter? Just proofroll, fix and compact.

Somebody with an engineering stamp needs to put their grown-up pants on; however.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Mad Mike]

Your query relates to the contractual use of Lump Sum for the earthworks contract.

I can't see the benefit to anyone of a Lump Sum earthworks contract- I would want to see a re-measurable contract based on the materials actually moved. On sites where the volumes of a certain material class (esp. hard rock) are not clearly defined and are likely to impact the contract price significantly, explain the risks to the Client and use this as a basis for recommending more detailed subsurface investigations...insufficient ground data is not a risk you should be absorbing.

All the best,
Mike

 

[Blairsy]

All great points above. Thanks!