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RE: Drilled Pier Spacing

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Richard,

	It all depends on cost, loads, and allowable bearing capacity.  I typically
assume about $35.00/ft for the drilled piers and $250.00/CY for structural
concrete (grade beams).  I may be way off so everyone please do not award me
any projects.  In any event, if you play with the numbers, you can come up
with a good feel for what is going to be the cheapest.
	I do a fair amount of design for expansive soils areas.  I have found that
with a 28' partially grouted cmu wall and about 30' of contributing roof, I
will typically use a 12"x30" grade beam with piers at 18'oc bearing into a
good rock at about 20' deep.

bks

> -----Original Message-----
> From: richard lewis [mailto:rlewistx(--nospam--at)juno.com]
> Sent: Saturday, November 02, 2002 4:33 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Drilled Pier Spacing
>
>
> I am doing a drilled pier foundation with grade beams in expansive soil.
> I typically don't do this so I am trying to find out some common design
> practices.  Basically I want to know what might be the target spacing of
> the drilled piers.  It is commercial construction.  What would be a good
> first trial value?  I was thinking of trying to stay in the neighborhood
> of 12 - 14 ft. o.c. and use 18" dia piers.  They need to go down about 12
> feet into the soil.  Should I be looking at a larger spacing of 18 - 20
> feet?  The wall construction is concrete filled foam forms.
>
> The advantage of the shorter spacing is the system is stiffer with less
> deflection, lower shear values.  The disadvantage is more drilled piers,
> higher deflection and shear values.
>
> Any other suggestions would be appreciated!
>
> Thanks!
>
> Rich
>
>
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