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RE: Enlarging a footing
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Enlarging a footing
- From: "Bill Allen" <T.W.Allen(--nospam--at)cox.net>
- Date: Mon, 8 Sep 2003 09:59:09 -0700
I totally agree with Jim’s concern.
I understand the desire not to disturb the existing soil, but
the new section of the footing will be disturbed and the amount of load it picks up will be suspect IMO.
Underpinning might not be so bad. You
could do it in four foot sections, alternating sections and doing it in two phases.
In the first phase, leave a section of bar protruding from each end to lap with
bars in the 2nd phase.
From: Jim Persing
September 08, 2003 9:45 AM
Subject: RE: Enlarging a footing
I always specify sandblasting or bush
hammering to 1/4" amplitude. But it can be spendy if you have a lot
of footing to do. Developing transverse bending moment stresses is not
especially nice, either. And you never know what the difference in true
bearing values are with freshly compacted soil adjacent to a footing that has
been there and settled for a length of time.
From: Gerard Madden, SE
Sent: Monday, September
08, 2003 9:09 AM
Subject: Enlarging a footing
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.