Grouted Tieback Anchors 1

[brokenpile]

We bid a projet for installing 25' long PZC 13 steel sheet piling with grouted hollow bar anchors 2".Bulkhead application with 12' exposed to the bay.Design Engineer plans show detail drawings as such and he noted the anchors to be 12' on center maxium with a waler.Wall design for 7000 psi per foot which we had to suppy a design for the anchors by another P.E.When we do our design the anchors have to be on 9.5' on center at a 30 degree angle 60' long with a 20' bond lenght to work.Since the bid plans noted anchors to be 12' on center maxium and we now know that they have to be on 9.5' maxium on center should the Owner be responsible for the additional anchors since we used the bid plan that was signed and sealed which noted the 12' OC notation for the anchors,stated sheet pile size and lenght, and grouted anchor to be used.The only two items not stated was the angle of the anchor and the lenght of the anchor.

 

[whyun]

Work out the final solution with the original engineer (or whomever is the engineer of record). Owner should pay for the number of anchors that ultimately gets installed.

 

[DRC1]

The first question is why can you not get the 12 feet? Generally, unless soil conditins are poor, you can install longer anchors for greater capacity. Also by using a 15 deg down angle, you get more horizontal force out of the same anchor. I don't understand how the inclination of the angle is not given, as that effcts the structural design of the waler system. You should be able to push the anchors out to 12 feet unless a specific capacity was given. This should be cheeaper than shorter smaller anchors. If I were the owner, based on what you have said, I would not pay for the additional anchors as the plans say anchors at 12 foot maximum. thus the design allows closer spacing. I would try to have your engineer and the designer work out the differences, but you should have had the anchors designed before you bid the wall.

 

[PEinc]

brokenpile,

What do you mean by 7000 psi per foot?

Also, did the contract documents require the anchor design to use any specific soil properties? If so, you probably will have to use them or more conservative values if more appropriate. If your PE chose the soil properties and tieback angle for his design, you need to check if he was too conservative. The tieback capacity will also be a function of the drill hole (drill bit) diameter. The bigger the diameter, the more bond area and capacity.

I am not a big fan of these hollow bar anchors. They are expensive to buy, limited in capacity compared to a solid bar or strand anchors, are not easy to corrosion protect, and it is hard to install an unbonded length over the couplings. It is also hard to use re-grout tubes with these anchors due to the couplings.

Normally, it is up to the tieback contractor to install an anchor that can do the job. The 12' maximum is most likely a function of the already designed tieback wale. Also, the anchor spacing is normally a multiple of the sheet pile double width. Therefore, the anchors are usually installed through the back flange of the sheet pile doubles when the wales are attached to the front flanges of the sheets.

 

[dik]

Whyun's got the answer...

Dik

 

[GeoPaveTraffic]

PEinc, good answer.

The owner is not going to pay more just because the contractor (or his/her) engineer comes up with another design. If you can prove that the anchors could not, under any conditions, be installed at 12 ft c-c then maybe you could get more money.

If you, as the contractor, were responsible for designing the anchors, then you should have designed them prior to putting your bid together for the project.

 

[PEinc]

The owner MIGHT pay (but I doubt it) for extra tieback anchors if they were bid as a unit price item. However, if the tiedback wall were bid on a lump sum or SF basis, too bad and good luck trying to get paid for extra, closer spaced anchors. It sounds to me like the owner does not care how many anchors are installed as long as they are not spaced more than 12' on center and the wale does not need to be redesigned at the owner's cost. This job is basically a performance spec as far as the tiebacks are concerned.

 

[brokenpile]

Thanks for all your replies,and yes we have poor soil conditions down to 25 feet before you get into the good sand so the 30 angle works the best to get to the good sand.Engineer of record no longer works for the design firm that supplied the bid drawings.All quotes for the anchors were based on the plans and the note about 12' OC maxium,so the design engineer must of felt that the anchors would work at 12' OC.Without that note on the drawings then anchor subcontractor would of work up their own calulations and number of anchors required.They also contest that the drawings are signed and sealed so we should be able to use them for construction.Everyone took for granted that since the soil borings were included in the specification and the Engineer specified the sheet pile size,tieback anchor type and the 12' OC note that he did a actual design to determine the 12' spacing.The only other explaination is that he just pick a number out of his "hat" and slaped it down on the drawings for no aparent reason.

 

[PEinc]

brokenpile,

I can't say that I agree with the second half of your last posting. It seems very clear to me that the contractor or anchor subcontractor is to design the anchors and use 12' as the MAXIMUM spacing. The designer doesn't seem to have designed the anchors. If he did, he would have had to give you the total anchor length, the drill hole diameter, the corrosion details, the design load, the anchor tendon type, tendon size, bearing plate size, etc. Did he give you that information? All that you said was specified is that the anchors are to be at 12' maximum and that should be based on the already designed tieback wales.

 

[whyun]

Scope of work is usually specified in the contract. Find out from the owner (or whomever paid for the design services) who was paid for the design of the tiebacks. Also, though not a part of the contract documents, a set of calculations is prepared to justify the design shown in the plans.

Are the plans showing 12 feet maximum approved by a local building official?

 

[ctcray]

you note "The only two items not stated was the angle of the anchor and the lenght of the anchor" but the REQUIRED spacing was not specified, only the MAXIMUM spacing. Sounds like whoever put the bid together missed that important distinction.

 

[brokenpile]

Question, Williams Form 2" hollow bar grouted anchor galvanize and installed as a tie back on steel sheeting marine application.... What would be the expected life span on the anchor?

 

[PEinc]

Life span would depend on the agressiveness of the soils, the thickness of the galvanizing, the size of the stell tendon, and the remaining sacrificial thickness of the tendon until the actual tendon load causes the tendon to break. Lots of variables and assumptions involved.

 

[brokenpile]

Thanks,alot of variables which we were sort of told by the manufacture also.Trying to sort through the temporary/permanent classification of these products.