Drill Concrete Pier - Bells
Drill Concrete Pier - Bells
(OP)
Designing a job on drilled concrete piers in Texas (expansive soils). What is the typical diameter (or most cost effective) and maximum bell diameter.
Looking a 12" diameter aprox. 10'-15' deep -- what can I use for a maximum bell diameter?
Jeff
Looking a 12" diameter aprox. 10'-15' deep -- what can I use for a maximum bell diameter?
Jeff






RE: Drill Concrete Pier - Bells
To answer your question - few inches on either side would be normal.
RE: Drill Concrete Pier - Bells
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Drill Concrete Pier - Bells
The geotech report should provide you with some guidance on this, but if I'm not mistaken, the bell is usually somewhere between two and three times the diameter of the shaft.
RE: Drill Concrete Pier - Bells
12" diameter is pretty small, at least for a commercial application. Would this be for a residential application?
RE: Drill Concrete Pier - Bells
When you get shallow, (such as your 10 feet) the bell may create an unsafe situation where the height of the bell might be susceptible to cave-in around the shaft at the surface. Also, at only 10 feet deep you aren't really getting the uplift anchorage from the bell anyway and the expansive clay uplift is also limited.
Bells are usually dug out with special drill cans that are exchanged on the Kelly bar for the typical drill "bit".
These have rotating cutter wedges that slowly extend out from the can as downward pressure is induced on the can. They cut into the surrounding ground and form the bell excavation at the bottom of the shaft.
RE: Drill Concrete Pier - Bells
The depth of pile is usually about 20 feet, but it can be much deeper if soil conditions dictate. Often the allowable bearing pressure for a belled pile is in the order of 8,000 to 12,000 psf in glacial till.
BA
RE: Drill Concrete Pier - Bells
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Drill Concrete Pier - Bells
3X is what I thought, but it has been awhile.
Jeff
RE: Drill Concrete Pier - Bells
A 12" shaft is pretty small in diameter for a drilled pier. That's more the auger-cast type (which cannot be belled). I have not asked for a bell in anything small than 30" diameter. In fact it's been my experience that most geotechs don't like to recommend shaft diamters for drilled piers which are less than 30". Smaller shafts are difficult to inspect.
RE: Drill Concrete Pier - Bells
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RE: Drill Concrete Pier - Bells