ACP Tolerance

[shepherd]

We have written the spec to allow a tolerance of 3" on the plan location of the top of the pile. The pile contractor in this case routinely is falling outside of this tolerance. This requires that we re-analyze caps. The largest variance has been 9". Is this large discrepancy common in the installation of ACP's? Has anyone ever seen a template used in drilling similar to that used in driving piles?

 

[BigHarvey]

I suppose ACP stands for Continuous Flight Auger piles. The European Norm allows for 100 mm ( 4 " ) tolerance for the position of the top of the pile.
With this tolerance you can still have piles outside the tolerance if the working platform or the soil contain underground obstacles. A bad quality platform will also lead to offsets because setting out pegs can move with rig and concrete trucks traffic.

 

[GeoPaveTraffic]

I've never seen a template used. I would say that 9 inches is excessive. Does the installers, or generals, contract require that the piles be installed to within 3 inches? If so simply back charge the contractor for the redesign. Once he sees a bill, you may see the tolerance improve.

 

[shepherd]

Thanks for the responses. The spec we wrote requires 3" max tolerance. In most cases the discrepancies are within 4"-6" and there have been no problems with cap capacity, but a few piles now have a service load above the design capacity. A load test program was completed and this doesn't appear to be much of a problem either. But when I saw the 9" discrepancies I was a little shocked that they could be this far off. If I had designed caps to the limit we may have needed to add piles to compensate for eccentricity. I wanted to know if that was a common occurence with ACP's, if so I'll compensate for more tolerance in design and specs the next time we utilize ACP's. That certainly wouldn't fly with anchor bolt or the column grid layout. Thanks.

 

[jgailla]

The tolerance depends on the size pile you are using. The grade beams won't move, so any error in plan location introduces eccentric loading to the pile. I have done ACP observations on a few piles, and there is no reason that a contractor can't get within 3" provided that conditions are applicable to using ACP piles in the first place. 9" is way off and should be backcharged. I recently was on a job where the 12" piles were apparently placed from 6" to 12" off plan. This led to grade beams not resting on some piles (bad contractor, he should've noticed) and the house is tilting so that it's almost unusable. It seems that 9" could cause problems in the future if the piles are less than 24" diameter.

 

[dmoler]

ACP=Augercast piles? 9" is way off, and you need to specify another pile for that pile cap to take the ecc. off it for the pile would be overstressed with that much off.

 

[shepherd]

Yes ACP = Auger cast piles. In this case they are 14" diameter. I have had to redesign and add piles do to eccentric loads. In most cases though the eccentricity hasn't been so critical (I had some cushion in the cap capacity). It's clear from the replies that this much out of tolerance is not commonly seen, and that's what I was trying to confirm.