cost of excavation

[Rjeffery]

How much should it cost to increase the depth of excavation for a 24 inch RCP (reinforced concrete pipe) originaly planned for 8 feet now scheduled for 8.75 feet? The soil is SM or CL or SC ie 'easy diggin'.' The run is 300 feet and unobstructed. It is in a green area where testing compaction is not required.

 

[jheidt2543]

The cost depends on the labor and equipment rates in your area. However, I can tell you that the deepest 9" of excavation is a LOT more expensive than the first 9"! Due to OSHA regulations, the trench must be wider, depending on soil type. So, you are not just excavating the 9" in the bottom of the trench, but also the sides of the trench. More excavated material, means more backfilling.

The backhoe needs to reach deeper for both excavting and setting the pipe. So, the added cost involved is not just for the digging, but for the setting of the pipe too.

Here in the midwest, excavation at that depth would be something like $15.00 to $18.00 per cubic yard out and backfilling with on site materials would be $6.00 - $8.50 back in, uncompacted. Here Operating Engineers get $48.00/hr and a large backhoe is about $95.00/hr.

It sounds like you are in a dispute with the contractor. Doesn't your contract have unit prices to go by?

Good luck.

 

[KRSServices]

It all comes down to the extra dirt the contractor has to move. Do your quantity takeoffs. Calculate the material to be moved at 8' and then calculate adding the extra 9". To go deeper requires more time and extra effort (stockpile, recompact, etc.). With the new quantities go for a scope change (if you have a contractor) to get agreement on the adjusted work. If you are doing a prejob estimate, then calculate the change based on the new volume of earthwork. The pricing will be based locally anyway, so any figure I provide will not likely be valid in your area.

KRS Services

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[Rjeffery]

The Change is a change to the GMP. there are no unit prices. the earthworks contractor has estimated something equivalent to 33% of his entire contract (which to him is lump sum) I can't see moving 6% more soil is worth 33% increase in fee.

OBTW Thank you guys (a gender neutral term) for the input. It has set me in the correct course.

 

[KRSServices]

Ahh...the beauty of a lump sum contract. You just learned the hard way why lump sum contracts are not suited well to excavation work without backup provisions for unit rates, or extra work/change of scope clauses. Without suffiecient backup, you really are at the mercy of the contractor. I quite agree, on the face of it, the additional excavation should not cost over a 1/3 of the original value. However, if the contractor has already de-mobilized or must make extra effort in the handling of the material (waste disposal, hauling, drying, etc.) or de-watering of the trenc, than additional costs can be expected.

In my contracts, I usually specify a range of depths for bidding (as a linear meter) as a unit price and reference these depths as the final price, to include all costs incidental to the work. That way, the contractor is bound to the terms of the contract and cost over runs are minimized due to special provisions and clauses intended to deal with additional/unforseen contract changes. It also eliminates the contractor's temptation to really stick it to the owner with outrageous costs. De-watering becomes a confidence item based on the soil logs.

KRS Services

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[DRC1]

Okay - OSHA reuires a 1.5: 1 slope. If the clay has some cohesion, the contractor may be running with less. However if we assume a 1.5:1 slope and asume a 4.5 ft wide trnch at the bottom, (a 24" pipe is actually 30 "+ at the bells),This gives you an area of 132 sq ft/ft of trench. If we go to 8.75 ft., the area becomes 154 sq. ft. The delta is 22% or 17%. If the reason for the deeper excavation is a change in grade in the pipe, the change in price should be on this order. If the change in price is due to unsuitable material under the pipe, Then that material yould have to be replaced. This would be about an 1/8 of a yard per foot. It sounds like the difference is 20% worst case. However since I havent, seen the job it is difficult to say that with for certian. Did the contractor ever give you a breakdown on the work? If he didn't, he should.

 

[KRSServices]

I know this point is moot, but if there is not sufficient documentation in the contract or specific references to unit costs, in terms of a lump sum and requested scope change, the contract can indeed specify his terms. I once had a contractor stick it to me on a lump sum contract. This contractor was very experienced and our engineer recommended a minor scope change, with consultation with the contractor to determine estimated costs, which I approved in principal. However, when it came time for the contractor to affx his signature to the change order, his price escalated 300% with no reasonable explanation. We re-evaluated the option and utilized our option of executing the work outside of the contract. That was our option, but it sounds as though it is not possible for you.

KRS Services

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[Rjeffery]

The contractor has elected to use a trench mule so the 1:1.5 slope is not an issue. The contractor has admitted that they have always intended to use a trench box (as the project is within eye shot of the local OSHA office!) that is why the amount is only about 6% greater not 17-20%. the client has agreed to spread the spoils over the site effectivly raising the grade 1/4 inch.

 

[KRSServices]

rjeffery,

From what you have stated, it appears that the contractor may be utilizing the weaknesses of a lump sum unit price as a mechanism to perhaps increase his profit margin. If the work has already commenced, as I suspect, I would be taking actions (which I care not to discuss on the internet) which could make the contractor a bit uncomfortable, but that's me. Otherwise, you may have no other recourse than to pay the higher price or reconsider the merit of the deeper excavation. One suggestion that I can make is to scrutinize the contract to ascertain any recourse with scope change, change of work, owner's rights to perform work, contractor's obligation and any special provisions.

KRS Services

http://www.krs-services.com