minimum size of drilled shaft

[DNBEA]

can anyone tell me the minimum size of a drilled shaft? Thanks.

 

[JAE]

I have a bit for my drill that is 1/8" diameter.

(sorry)

For drilled piers or auger cast piling, micro piling, etc. the minimum size probably depends upon what is available from your local drillers.

Well drillers can go to 4" I think.

 

[DNBEA]

haha! wiki says minimum is 18". I believe it.

 

[hokie66]

There are a lot of types of bored piles. I have seen Franki expanded base piles with a shaft diameter of 350 mm, or about 14".

 

[JAE]

Auger cast piling - have seen them at 12" diameter. But again - just check with the local drillers to see what they can offer.

 

[abusementpark]

Based on my experience it is 18", but I even heard that contractors don't like them this small. We recently changed all our 18" shafts on a job to 24" just based on a contractor's recommendation on constructibility.

 

[BigHarvey]

Auger Cast piling : 12"
Bored piles with bentonitic mud : 24" ( because of the size of the kelly bar )

 

[emmgjld]

When dealing with expansive soils, smaller is better, to reduce the uplift forces of the shaft side.
In Colorado I have seen thousand of residential projects with shafts of 8", 10" and 12". A lot of care is needed to construct these.

 

[csd72]

Call a local contractor and ask.

I have seen them down to 12"

 

[dik]

We often use 12 or 16" dia in these environs... and about 30" dia for sleeve access.

Dik

 

[Teguci]

In cases where the shaft is resting on rock, a downhole inspection is sometimes required. On these occasions it is good to be a large person.

30" min, 36" for the larger people. Reference FHWA - Drilled Shafts.

 

[Riggly]

According to FHWA it can be as small as 12" but length should be limited to 8 to 10 feet. However, the document did not specify that a drill shaft cannot be less than 12". However, as a matter a practicality, I don't think it will be smaller.