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Re: Enlarging a footing

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Would compressed air work? If the soil doesn't have much moisture in it, I'd think the compressed air could adequately clean the concrete surface of all foreign material.

I'm assuming your increased width is close to the full 30" depth? Flexure of the footer, perpendicular to the cold joint may be an issue if it's only 12 - 14 inches thick.

Steve P

On 9/8/2003 9:08 AM after considerable forethought, Gerard Madden, SE wrote:

I am trying to enlarge an existing strip footing by increasing its width. I have proposed to place new concrete on either side of the existing footing thus doubling its width. The existing footing is 2ft widex2ft-6in deep and I have called for shear friction dowels on each side (2 rows, ea. Side) to share the bearing with the new concrete on either side.

The plan checker is questioning the surface preparation of the existing concrete and how that is going to be achieved. He wants underpinning – since the existing footing has not failed or shown any signs of settlement, I think increased bearing is an appropriate solution rather than deepening the foundation. Underpinning would require shoring and an increase in cost and possible disruption of service for the tenant. Underpinning would also change the distribution of shear and moment in the existing footing, it’s capacity may not be up to snuff.

Can anyone recommend a dry method of surface preparation to enlarge the footing as I described? The concern is hydraulic methods of surface preparation would saturate the soil.



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