Loads for Pile Design

I have never encountered this in any design I reviewed, or which I did personally. I don't think that this is typically designed for specifically. I guess that most of us simply assume that the various factors of safety built in at multiple steps will accommodate this eccentric load. That is one reason it is typically limited to the 3" (75mm) value.
Dave

Thaidavid

A little off topic, but I had a timber pile project where the piles were off as much as 13 inches. The GC had 0 pile experience and did no oversight of the installation process. Add in the face that the geotechnical engineer reduced the capacities of the piles to suit the loading conditions. All this added up to my problem and the project being a complete disaster.

In the US there is a note in the code about a 10% over stress in the as built position of the pile being ok.

JC456 said:

i.e. for a 2 pile cap assuming that the piles can both be out of place by the standard 75mm...

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When possible, avoid the issue. Use 3-pile (or more) caps. Then pile placement, within tolerance, becomes part of the normal safety factor for pile design.

With a 2-pile cap, the problem is not just potential overload of one pile, but also eccentric loading on the cap. In my sketch below, both piles have been installed within the 75 mm tolerance. However both just happen to be off in the same (sideways) direction. IMHO, the eccentric loading is more of a problem than the possible 10% overload you mentioned.

Don't assume that a drawing note requiring a tighter tolerance will solve the problem. Speaking as a former bridge contractor, keeping a pile within the 75 mm tolerance requires skilled / experienced workers.

Thanks for the replies.
I am only referring to worst cases for proportioned loads from pile tolerance.
Torsion in the 2 pile caps in the other plane (i.e. if both of out of place to the same side) I always deal with by providing tie beams or ensuring the slab is reinforced to resist this.
The 75mm out of position plus 1/75 inclined tolerance dependent on depth is fairly standard for CFA piles. Depending on depth from piling level to cut off level the pile could be quite a bit more out of position.
We wouldn't need to tighten tolerances as all easily dealt with. I was mainly interested in what other engineers allow for in these instances. From SteelPE's response it sounds like the US codes deal with this for the majority of situations but I am not aware of anything similar in UK or European standards.

I have designed building foundations with an assumed as-built eccentricity of 3" in any direction. I documented that tolerance in the contract documents and when I reviewed the as-built locations, any pile cap with an eccentricity of 3" or less was OK'd with ease. With the added eccentricity, some of the design pile caps needed to have an extra pile added. On one project, the geotech offered the owner a competing design which did not account for the additional as-built eccentricity and noticeably required fewer piles. My design was still the one that was installed.