Drilled Pier Cold Joint

[IceVol]

A Contractor of mine poured the first 25 feet of a 3' dia 30' drilled pier foundation designed to support a steel lattice transmission structure before he realized the foundation was off by the correct drilling location by about a foot. Construction halted and the top 5' haven't been poured and the anchor bolts have not been set. The anchor bolts can be placed in the correct location within the rebar cage, but obviously the required clear cover to the anchor bolt is inadequate for loading.

My inclination is to demand that the foundation be dug up and reconstructed, but the contractor insist that forming up an additional foot around the correct anchor bolt location will be adequate. What sources can I quote considering the obvious cold joint will be exactly where the tension and compression failure cone will be? I don't doubt that a solution could be made without digging up the mistake I'm just having difficulty finding sources on construction joint in drilled piers.

I know that a drilled pier is just a continuously supported column and construction joints can occur at the intersection of beams and columns yet I imagine this is a different case where the cold joint is in the most undesirable and unplanned place. What source details the connection of emergency cold joints?

 

[IceVol]

This does not specifically address drilled piers but its a start.

ACI Committee 309, “Guide for Consolidation of Concrete (ACI 309R-05),”
American Concrete Institute, Farmington Hills, MI, 2005, p. 19.

 

[grabens]

I had a similar occurance happen once with a drilled shaft foudation when a tremie pipe got stuck and the shaft was unable to be finished in a timely manner. The contractor ultimately applied an appoxy at the cold joint and finished pouring the shaft. However, as the geotech of record, my company and I insisted that they construct two sister shafts on each side of the defective shaft.

I would be nervous in your case with what is being proposed. I would insisted they install a new shaft or sister shafts. Contractors are always trying to put the liability on the engineer to cover up for their mistake. There is a reason why cold joints in drilled foundations are not a standard of practice whether you know the reason or not!

 

[emmgjld]

Placing a cold joint must be carefully thought out. As mentioned above, cold joints are not common and I believe should be planned. I think a sister pier(s) is usually desirable. Pulling or excavating around the pier location tends to 'butcher' the soil structure.

 

[hokie66]

I don't share the reluctance to save the portion of the pier which has been placed. A cold joint itself has little to do with the compressive capacity of the pier, and as this is a transmission tower, I imagine the controlling force will be tension. Surely the 25' at the bottom of a 30' long tension pile contribute most of the capacity, and it is the reinforcement which carries the tension.

 

[TXStructural]

You need to redesign the pier with the offset. Do not just make the top of the pier larger unless the pier can take the offset. And if the soils are the least bit expansive, you will need to make sure the potential uplift due to soil swelling is countered by some reasonable strategy. With non-expansive soils and sufficient capacity for bending, a larger pier cap may well be acceptable.

If the soil permits, you might need to either install a parallel pier or connect the adjacent pier on the same tower to counter any off-center loads.

As for the cold joint, make sure the surface of the existing is clean and the reinforcement is clean and in good condition. Make certain that the reinforcement extends a full development length into the concrete above the joint (or as required for uplift), and the anchor bolts lap an appropriate length with the reinforcement. If there is doubt about this, hooks or field installed heads can be put on the bars to anchor the concrete above the joint to the pier below.

 

[Drumchaser]

I would insist on the "sister shafts" w/tiebeam across the bogey shaft.