12" Diameter Concrete Piers

[Sean_14]

I am designing a staircase outside climbing a hill and due to clearance issues for installation the client wants to use 12" diameter piers roughly 5' in height (3' into the ground). The load is minimal about 3 kip vertical but I am concerned about spalling and the rebar fitting with enough cover. Any ideas if this will work??

 

[SlideRuleEra]

The load is minimal about 3 kip vertical...

Soil bearing area of the 12" diameter pier is about 0.79 ft[sup]2[/sup] which is 3.8 kips/ft[sup]2[/sup]. Is the soil satisfactory for this load?

If the concrete pier is placed directly against soil, 3" of concrete cover is appropriate. If it is formed (Sonotube) and backfilled, 1.5" cover (#5 rebar, or smaller) on the sides and 3" on the bottom should be fine. What is your concern?

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[dhengr]

Sean_14:
Is this an industrial strength (OSHA compliant) stairway at 100lbs./sq.ft. plus DL’s., etc, or is it a sidehill stairway a at the cabin or the beach? Is that 3k per pier or 3k on four or six piers over the full length. Use slightly larger dia. sono-tubes and small dia. tied cages of vert. rebars. Place 6-8” of conc. in the bottom of the form and place the rebar cage in the center and support it at the top, and fill the form. Alternatively, a couple treated 6x6 posts with a 4x4 or 4x6 cross member bolted into a notched post (for good beam bearing) works pretty well at the cabin.

Aside from the structural/foundation issues, my biggest concern would be that the contractor disturb the hillside, top soil and vegetation as little as possible and make final provisions and grading details so that this stairway does not turn into an eroded washout in a couple years.