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pros/cons drilled pier vs spread footing

pros/cons drilled pier vs spread footing

RE: pros/cons drilled pier vs spread footing

Are you talking straight shaft bored pier or belled pier?

RE: pros/cons drilled pier vs spread footing

(OP)
straight not belled. skin friction is considered.

RE: pros/cons drilled pier vs spread footing

In that case, assuming the frost action is taken care of (i.e. footing below frost, and friction piles long enough to negate the frost action) and assuming this is on some sort of clay and not bedrock.

Footing:
Pro: easy to construct, generally less concrete, can be excavated and backfilled with equipment already on site.
Cons: Subject to vertical movement, require lots of excavation (depending on frost depth), low capacity (depending on bearing material)

Friction Piles:
Pro: Negligible vertical movement, generally high capacity (depending on skin friction)
Cons: More concrete than footings, require specialized equipment to drill

There are more pros and cons for each but that's my quick version.

In the end, the biggest factor in which foundation type to choose is the soil characteristics. If you're in a 60 foot deep chunk of sloppy clay, then piles are a must, if bedrock is near the surface, then pads are a no brainer.

There's no perfect solution that will encompass all situations.

RE: pros/cons drilled pier vs spread footing

Based on your sizes, I like the drill because it's a one step pour. No joint, no forms, no backfill. Biggest con I see is potential availability of drill rig. But you wouldn't need something very big for this at all.

Much of it will depend on the quantity. If you only need 1 or 2 I'd probably go with the spread.

You could always detail both and let the contractors bid them based on which they prefer.

RE: pros/cons drilled pier vs spread footing

I didn't even open the sketch.

7 feet isn't very deep for a friction pile. Is there a chance of frost? How deep?

RE: pros/cons drilled pier vs spread footing

(OP)
@azcats, i was told you can use a backhoe with a drill. i'm not sure though what's the maximum lenght it can go.

RE: pros/cons drilled pier vs spread footing

You can get a 7 foot drill attachment for a backhoe

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