# RE: Footing sliding resistance - Friction

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Footing sliding resistance - Friction
• From: "Christopher Haffner" <chaffner(--nospam--at)gorge.net>
• Date: Mon, 20 Jun 2005 13:16:55 -0700
```Thanks all.  You have confirmed my thinking on the footing/soil interface
values.

Does anyone count on the fill (granular or compacted) below a slab (a 1' to
6' wedge in this case) as adding any sliding resistance if the original
grade is benched?  There has to be some added benefit.  I don't think I need
it in this case but it would be good to know for future reference.

Chris

Haffner Consulting Engineering
www.haffnerconsulting.com
Office & Fax:  541-478-3052

-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Monday, June 20, 2005 12:24 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Footing sliding resistance - Friction

Christopher,

The coefficient of friction of 0.45 simply means that 45% of the
related to the width of footing, HOWEVER, the weight of footing can also be
included in the vertical load as can the weight of backfill on top of the
footing.  As a result, increasing the footing width will also increase the

Regards,

H. Daryl Richardson

----- Original Message -----
From: "Christopher Haffner" <chaffner(--nospam--at)gorge.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Monday, June 20, 2005 12:50 PM
Subject: Footing sliding resistance - Friction

I'm having a Monday morning brain freeze and thought this was a no-brainer
but can't find a definitive answer.

I am being told by the Geologist on a sloping (2H:1V) residential lot that
the coefficient of friction is .45 (no units).  He is also indicating that a
wider footing will add some needed resistance to sliding.

I don't think this is correct in that the coefficient should only depend on
the amount of gravity (vertical) load and not on the area of the bearing
area.  Therefore, making my footings wider won't really help my sliding
problem other than to add a little more weight.  Am I thinking clearly here?

Another question.......I will have some granular fill (varies from 1' to 6'
thick) below a basement floor slab.  I think this helps my sliding
resistance by adding weight to the system as it interfaces with the soil
below.  Since I am having the slope benched I would like to use this
resistance (weight x coef of frict).  Opinions????????

Chris

Haffner Consulting Engineering
www.haffnerconsulting.com
Office & Fax:  541-478-3052

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