Pile Groups

[rendevouspoo]

Is there a standard code for the design of Pile Groups? I haven't been able to find anything. I'm unsure as to how design them as opposed to one drilled concrete pile. Do you guys know of any design guides or sites that are any help? ACI states to not use their standards for the design of drilled piers. I can't find anything on the design of the reinforcement either. I was under the assumption that you would use ACI column design for the reinforcement until I found that ACI states not to use their code for it. Any ideas?

Thanks!

 

[TLHS]

So it sounds like you're doing a pile group of augered concrete piles.

First off, if you're not familiar with design of pile groups (and even if you are) it often makes sense to just get the geotech to do as much as possible. Work out force and deflection limits and any construction limitations and let them go to town on the pile group. Then you can get the internal forces from them and do the structural design.

If it's just simple axial loads with limited lateral contribution, you can probably get away with just having the geotech give you some design values to use as a basis.

As far as construction details, there seems to be a large variance for augered piles depending on location. Maximum size seems to vary a reasonable amount, as does reinforcement. In some places, it's typical to only reinforce augured piles when there is a tension or moment force in them. In these areas it's typical to drop a single centre piece of reinforcement to develop tension resistence, and obviously include a cage if there's moment in the pile (some people will only drop the cage to the depth where your pile is no longer significantly contributing to the lateral resistence).

In other places, most engineers will include a full cage of some minimum size regardless of the forces in the pile. This is certainly something you'd likely want to do in a seismic area.

I'm not sure about the ACI code, but the Canadian code certainly has some level of instruction on piles, and I believe it even has an example. A lot of the code isn't necessarily applicable though.