drilled piers

[nuche1973]

Greetings all,
I put a call into my local contractor, but figured since I'm waiting I'd ask. I am looking at a foundation wall, 12" thick and 13' deep. Next to this is a 3' dia. drilled pier (or pile) that is 8' deep. The distance from the edge of pier to wall face is 12" +/- 2". Taking into account the drilling rig bit and head. It seems to me that this would be difficult to implement. Am I correct?

The loads involved with the pier are small, around 7.5kip combined dead and live. The soil against the foundation is back-fill and not in-situ. As always any insight would be greatly appreciated.

 

[civilperson]

Why so big of diameter for 7.5 kip load, (try 8" diameter pipe pile)? Some drill rigs can get very close to obstructions.

 

[jike]

You will be within the backfill zone of the wall. I assume this is granular material. Can it be drilled in that wiothout a casing?

Is there a better solution like building a haunch on the wall? Or forming and pouring a pier down to the existing wall footing.

 

[nuche1973]

Civilperson,
The pier size was necessary to accomodate architectural cladding over the column. It's more for bearing surface than loading.

Jike,
How would that affect the existing foundation?

 

[nuche1973]

I forgot to ask: I assume that this will put a surcharge load on my wall (which I'd need to check) correct?

 

[jike]

I can't answer how it would affect the footing. You will have to evaluate that.

If the pier does not extend to the base of the wall, then you would need to evaluate surcharge on the wall.

 

[nuche1973]

Thanks for the information. I appreicate it.

 

[LPPE]

I did a job with drilled piers recently right up against an existing building on a property line. The drilled pier contractor I worked with needed one foot clear to work with. Looks like you've got your 12" clear. Of course, more room is better if you can get it.

 

[SkiisAndBikes]

If the drilled pier is founded at 8' depth it will bear on backfill and settlement can be expected. Also, it will add surcharge to the existing foundation wall if only drilled to 8' depth. If the pier is founded at the same depth as the existing strip footing the settlement and surcharge issues disappear.

If the pier is drilled within 2" of the foundation wall and extends down to the bottom of the strip footing (12'), will it overlap the footing projection?

What about the weeping tile at footing level?

Could helical piles be considered with a 3 ft. diameter pile cap?