Tied Backed Intregral Abutment 2

[facca]

I am a bridge contactor hired by a highway agency to construct a semiintregal abutment structure designed by the highway agencies consultant.This abutment is supported on caissons founded on rock and tied back with a proprietary system.Caissons are already installed and the next phase of the project well involve installing the tie back wall and then constructing abutment and anchoring it to the tie back wall.The contract stated the our supplier was to provide a statement of satisfactory internal & external stability.Our suppliers goetech firm statement was as follows the design of the 2h:1v cut slopes were found to have insufficient stability based on parameters provided in the soil report and it is not possible to achieve adequate global stability with any structure associated with this slope.My problem is that I am being told that it is my responsiblity to provide adequate global stability. I am only a contractor not a designer.Any insights would be helpful.

 

[PEinc]

It sounds to me like you, your supplier(tieback contractor?), and your supplier's geotech need to meet in person with the agency's consultant to discuss the design parameters, design method, required safety factors, and the original analysis performed by the agency's consultant in developing the original bridge concept.

I don't understand why you were allowed to install the caissons if the total design was not yet approved. Could a redesign of the slope also affect the design of the caissons? Is there enough room to redesign slopes? Exactly what did the agency's consultant design? I'm surprised that you were not responsible only for the design of the tieback anchors. I've never seen a contractor also responsible for the stability of slopes shown on the contract documents.

 

[cap4000]

All I can say is WOW!! Why did the geotech firm wait so long to inform of this soil rotational stability dilemma. Somehow, Geosynthetic Fabrics must be installed (if he is right) before you proceed with the tie-backs. Get another PE Geotech with computer modelling expertise. After that get LAWYERED-UP. What earthquake zone are you in and where is the water table?? When was the Soils Report actually read the Supplier/Geotech? Can you describe your field conditions further? Good Luck!!

 

[DRC1]

I truly feel your pain. I just finished batteling a similar situation that occured in several years ago. Unfortunately,it appears highway agencies do not want their consultants to take responibility for design and are requiring the contractor to submit P.E. sealed drawings of the designs described in the bid.If the system was for the most part described in the bidding documents I think you are ok. It has been pretty well established that as the bidder you are responsible for pricing the work shown and not checking the design. If the bid documents were more conceptual, and it was clear you would be actually desiging the work (as oposed to checking the work) the road may be a little rougher. If this situation is worth a lot of money, and I suspect it is, go see a GOOD construction lawyer. Plan to spend some time and money bring him up to speed. Maitain and share on a daily basis contempory cost records of every thing you think is an extra to the contract. Make sure you share the records, even if the inspector does not want them. Because your records were shared, they will be given much more weight.
Document the existing conditions. Take pictures and video of everything. Document all directions and conversations in writting. Reguardless of weather or not the agency recognizes the change as extra work, you probably have an obligation to perform. Even if you don't, things wont get better just sitting. Find a safe econmical solution to the problem, do it and get the job moving. Agree with the agency to disagree and get moving. Don't fight until after the problem is solved. You should probably get a second opinion from a reputable geotech (although you don't want one that does a lot of business with the agency)I would do this now so you can get a clearer idea of your situation and to make sure your geotech is not missing something.
Good Luck and please keep us posted. By the way, which state is this in?

 

[BigH]

Global stability vs internal stability of RE or MSE Walls? Used to be that RE only guaranteed internal stability - the external stability was a requirement of the design consultant - such as he would be if RCC wall was used. I know, there is a lot of buck passing . . . Make sure you follow the contract - not just the "desire" of the agency/designer. Are you actually required contractually to guarantee global stability? If so - this must have been clearly stated at the time of the bid - did you ask this question in the pre-bid meetings? It is onerous to contractor's to guarantee overall stability - they had/have no time to do proper investigations, etc. at time of bid to cover this item should there be a fubar.

 

[PEinc]

BigH is correct. However, facca did not indicate that this project was using an RE or MSE abutment. This makes it even odder that the agency is asking the contractor to assure global stability. Something is confusing or someone is confused here. My guess is that the agency and their consultant are confused and have little experience with "alternate" bridge structures. We (including facca) need to know more.

 

[Focht3]

DITTO. Give us more information. Something sounds screwy - it sounds like you are getting hosed. BUT we need more information...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[facca]

Thanks everyone for your help.We installed the caissons last fall and then open the road to full traffic.We are scheduled to start back in mid April.The design consultant
RE supplier and soil consultant all developed this design and the designers sealed the design.Slopes cannot be redesigned due to the waterway and the plate girders are already fabricated.Metric N values are in the range of 7 to 11,silty loose to compact.Job is located in Ontario.The RE supplier was single sourced by the designers with no option to use anyone else.We are required to provide a statement of satisfactory external stability,not a requirement to guarantee.On integral abutments it is my understanding that the embankment is a critical aspect of the structure.The design consultant and RE supplier are very knowledgable on this type of structure.The depth of the silt and slope is around 15'.

 

[PEinc]

I'm a bit confused. Why do you have all of these: MSE wall, caissons, tiedback wall, and slopes????? Why does the bridge need each of these?

Is a slope in front of the MSE wall not stable? If so, maybe the MSE wall needs to be founded deeper and the height of slope needs to be decreased until the slope is stable.

Where are the caissons and tieback wall?

But I do agree with Focht3. It sounds like you are getting hosed unless the specs were very clear on the design responsibilities. If the "designers sealed the design" already, why are you responsible for a portion of the design that so greatly influences the balance of the structure design?

 

[facca]

The caissons support the abutment,the RE tie backs supports
the backfill behind the false abutment,the slope protects the stability of the structure since these structures have no tradional footings and in this case rely on the embankment for stability.I don't want to touch the design but my hand is being forced no one likes delays I would love to work on a solution instead of arguing on language.The owner
doesn't have the expertise on board yet to realize the seriousness of this issue.

 

[Focht3]

Have you hired your own geotechnical consultant? Do so NOW - you need a really good one.

And hire a very competent construction lawyer ('solicitor'). It sounds like you will need a good one of those, too. And re-read [blue]DRC1[/blue]'s March 27, 2004 post. Follow his recommendations on documentation 200 percent.

Good luck - let us know what happens!



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[facca]

I do have a goetech firm on board and they concur that the owner is being heavy handed.I will take care of the legal by staying away from the lawyers. This issue is way over there head.

 

[Focht3]

You need a good construction lawyer. S/he can help you 'nip this one in the bud' (it's spring, right?) before it gets out of hand...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[layfieldman]

This sounds quite similar to a project that is occuring in my neighbourhood. Same thing in that the original design did not consider global stability. The owner says it's the prime contractors responsibility, the prime contractor says it's the RE sub-contractors responsibility and the RE sub says it's everyone elses responsibility.
If you are in Ontario working on an abutment then I'm pretty sure which company you are dealing with as there is only one approved RE structure for your type of project in the Province.
As in your case this project is being stalled for the same reasons but the prime has decided to find an alternate solution in using a fully reinforced slope as opposed to a combination of slope and wall. This will hopefully allow the job to go ahead with only slightly above budget instead of the quite expensive cost of adding additional reinforcement in addition to the designed wall/slope system. This is possible here in my area but might not be in yours.
As DRC1 as stated though, whether the new system is approved or not they will proceed with the job even if they have to use the original design with the additional cost. State/Provincial DOT's are usually the largest owner in any area and it's not a good idea to but heads with them unless unavoidable.

 

[DRC1]

I would encourage you to see your attorney. This does not sound like it is headed anywhere good. You don't have to rush into court right now, or even ever, but your attorney can give you proper advise to a.) maintain your rights to pursue collection and b) not assume unnessary liability for someone else's work. Granted, noone wants to be in this postion, but you are anyway. A good construction attorney will help you be sure the written record reflects the facts important to your postion.

 

[VAD]

Hello facca:

What is insufficient stability of the 2:1 slope. Is this a condition of less than FOS of 1.5. For a 15ft high cut slope a 2:1 slope seems reasonable based on my experience despite not knowing the ground conditions that well. Very often although a FOS of 1.5 may be desirable, one can live with lower FOS such as 1.2. Many slope stability analyses really have to be looked at carefully especially parameters that are being used. The GIGO term is especially applicable here.

What is the disposition of the likely failure. Use this information to assess the problem. You may be able to see that very little has to be done to offset the predicted failure.

Will the slope failure or likely creep of the slope be taken by the abutment backwall and piles. Does the design cater for this aspect. This should be addresed with the design consultant.

Interesting problem. Your geotechnical consultant does not seem to say much apart from the owner is heavy handed. What are his views on the problem of stability and structure performance. Meat and potatoes are needed. You probably need a structural consultant to evaluate as well since distress to the integral abutment is where you might swing as you are responsible for producing a product that is free from defects. The idea of founding the pile in rock may not allow the slight movements which may be needed to offset the forces due to expansion, forces due to slope creep etc.

Interesting topic. Better reviews and info would be possible if the drawings are seen.