Several years ago I did quite a bit of foundation design for the structures I designed but haven’t done a lot lately. I recently designed a large structure that is being erected in Australia and I was asked to review the foundation design that was done by a local company. Since there were large uplift forces on some of the columns, they used drilled piers for the foundation. They gave two schedules that depended on the “shaft roughness class”. Apparently they were doing something to the sides of the soil to increase the friction value. The pier diameters were 30” and the depth was for example 12’ for one roughness and 30’ for the plain drilled shift. I’m used to surface uplift friction values of 200-600 psf. That value was about right for the deep shafts but worked out to be up to 1800 psf for the shallow shafts. Has anyone heard of this ‘roughening’ of the shaft sides to produce considerably more skin friction for uplift?
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