Auger Cast Piles in Louisiana

[laneng]

I am designing a 5 story, post tensioned concrete building located a few blocks from the Quarter in New Orleans. Due to the amount of older historical buildings in the area, we are using 95’ deep auger cast piles rather than driven piles to keep the vibration at a minimum. We are showing a full length #11 centralizer bar with a basket at the bottom to be installed in all piles. I am also showing 10’ of reinforcement in the typical pile, and full length reinforcement in the piles supporting the shear walls, all of which is common practice here in Chicago.

We are currently in the bid process and have been informed by about 10 contractors that no one uses full length reinforcement in New Orleans, not even the centralizer bar. All of these contractors are passing on the project. From reading a few of the other posts, especially Auger Cast Piles thread256-91394, most engineers seem to be pretty big fans of centralizers.

I spoke to our local soils engineer in New Orleans who told me that more often than not, centralizer bars are used in auger cast pile construction. He also agreed that reinforcement is typically placed in piles supporting the shear walls, (I didn’t think this issue would be negotiable, but I asked him anyway). I can verify my calcs again to check on whether it needs to be full length, but in glancing at the boring logs, there point of fixity seems to be little deeper than most locations around the country, to say the least.

I would tend to believe a licensed geotech engineer in this case, but can any local New Orleans structural or geotechnical engineers give me your two cents on the matter?

 

[motorbiketocrank]

I don’t have local experience but I’ll thow out a couple thoughts in the hopes it will help. I would agree that you’d need the full length reinforcing for the scenario you present. But the bigger picture questions that spring to my mind would be on the overall pile selection and constructability issues. Did the local soils engineer you mention comment on whether the auger cast piles in that area are commonly installed to the near 100’ depths you’re planning on and for similarly loaded structures?

While I don’t know the soil conditions at your exact site, discussion of New Orleans instantly brings up mental images of signficant zones of very soft, organic soils. Was negative skin friction (NSF) accounted for In your design? Auger cast piles are often undesireable in soft soils as bulges, etc in the pile from the construction technique can lead to very high NSF loads. (on a side note, NSF loading can be one factor in the need for full length reinforcing in auger cast.)

Another question is whether you can install the desired reinforcing to the full pile depth. My experience is typically with piles less that 50’ deep. But I can attest that on some of those jobs it’s been difficult to get the reinforcing in place. Obviously the deeper you have to push the reinforcing into the grout the more resistance you have. Maintaining vertical alignment as you are trying to push the reinforcing in also can become difficult.

Sorry to answer your questions with more questions but figured some of these issues may play into your problem. Perhaps the contractor’s are used to installing shorter piles for more lightly loaded applications such as residential where they don’t really have to worry with the same risks, lateral loads, etc? I agree some input on common local practice from practicing engineers in the area would be valuable. I’m not sure what contractor’s you’re dealing with but some of the larger firms that are highly specialized with good reputations and engineering staff can also frequently give great advice.

 

[jgailla]

I have seen centralizer bars installed with no problems in auger cast piles over 80' deep in southeast Georgia in a marsh environment.
The problems seem to come with the reinforcing cage.
The longest reinforcing cage I have seen was 35', and they had a real problem installing many of them without using a trackhoe to jam the cage down.
You could consider contacting Berkel. They have lots of experience with auger cast piles.

 

[jdonville]

laneng,

It is extremely difficult to put any sort of cage of any significant length into an augercast pile. Having worked in Chi-town, I am familiar with long cages in drilled shafts.

The difference in the case of ACIP piles is that you have all that grout to push the cage through, which is just not constructable.

Suggest you explore altering the geometry of the deep foundation elements or maybe even using barettes or tangent/secant ACIP pile coffers to get a workable solution for your shear wall foundation (just talking off the top of my head here).

Cajun Constructors and Berkel (to name 2 DFI member firms, there are likely others in the 10 you have talked with, as well) have a good deal of experience in NOLA and you should try to take advantage of their experience. Ask them what they think might work - they have in-house expertise that could help you arrive at a constructable solution that meets your structural/geotechnical criteria. Consider using a design-build approach with a performance-based specification.

DFI (

http://www.dfi.org),

ASFE and maybe even ADSC have specification and contract guidance available.

Jeff