Who specifies the top of caissons?

[twheng]

With a structure entirely on drilled piers on a sloping site. Who is responsible for determining the top of the pier? The structural or the contractor?
Thanks

 

[a2mfk]

The architect determines the finished floor height, then you work your way down your structure to come up with the TO pier. So the engineer does via the architect...

 

[twheng]

Thanks,
For the help and if the project was a simple slab on grade or flat it is a very simple addition or subtraction calculations based on the architects elevations. If the site is on a steep slope and we need to rely on the outside finish grade (Which has never been exact as long as i have been doing this). Then we are at risk for a caisson that is too high or too low.
Would you still specify the heights?

 

[a2mfk]

I am not sure I understand your question, but what I would do is specify my floor height for a RELATIVE elevation, for example 100'-0", and then specify the top of caisson in terms of that. This is what is usually done in the US at least for elevations of structures. Then the civil engineer gives the exact elevation based on the survey info, and the contractor coordinates all of this.

You may also need some CYA notes like "field coordinate" and/or "report actual elevations to structural engineer prior to construction" so that you can make sure you are OK with all of your design based on the actual site conditions. But I guess this would only affect your column height not much else.

 

[twheng]

Thanks a2mfk

You got the idea but the contractor wants the elevations and we are reluctant. We can easily provide the top of caissons with respect to the outside grade. This is basically a few additions or subtractions from our details. Most of the contractors we work with have no problem. We have done over 100 caisson projects, and this one wants us to provide this. If this is the industry standard then we will be more then happy to provide this but I could not find anything in writing who is suppose to do this.

 

[msquared48]

If you have to, and really you should, show a general detail with the caisson (augercast pile?) on a slope and detail how far the top is to be above the upslope (6" to 1 foot?).

Mike McCann
MMC Engineering

 

[hokie66]

The contractor needs to do his work. Give him the parameters, but he needs to be responsible for setout of the job.

 

[twheng]

hokie66
This is exactly our position, but we were looking for some backup (paper) to explain to him that he needs to do this. We have provided all the details necessary for the contractor to do the math. I think he as never installed caissons before.
Thom

 

[a2mfk]

I would not want to be part of his learning process, and I would tell your client about your concerns. Typically SEs do not provide many dimensions or elevations, this is left up to the architect, civil engineer/survey, and the contractor to coordinate.

Is the top of the caisson going to extend above grade and serve as the column also? If not, and there will be a column and cap placed over top, then I wouldn't see a need be tied down to a specific elevation of the caisson...

Stick to your guns, he needs to field coordinate this, not you.

 

[csd72]

You may have a survey but you do not know the exact levels of the entire site. Give a bench mark level and let the contractor figure out the rest.

 

[SteelPE]

If your company has done over 100 projects with this type of foundation system then I would think you would be writing the standard.

The contractor is probably trying put some of his responsibility onto your company. Then if something goes wrong, it's just a change order back to the owner.

 

[csd72]

SteelPE,

Contractors wouldnt do that would they?