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RE: Footing Overturning in Rock

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Dywidag supplies both grouted rock anchors and resin anchored rock bolts.  Resin anchored rock bolts are not uncommon in tunnel roofs to stabilize the rock and can be used as tiedowns.
I've used mechanical rock anchors (with an expansion head) to tie down a slab against uplift due to water pressure a number of years ago.  The anchors were preloaded/ prestressed and some of the anchors were slipping at a load lower than the required preload.  Apparently the rock was too hard (and smooth), and the expansion head had a hard time gripping into the rock.
Bill Sherman

From: Rich Lewis [mailto:seaint03(--nospam--at)]
Sent: Tuesday, July 18, 2006 11:04 AM
To: seaint(--nospam--at)
Subject: RE: Footing Overturning in Rock



I’m not sure if you are kidding or serious.  How common are epoxy rock anchors?  I haven’t seen them used before.  I have been to the Williams site and looked at their literature.  It seems to me that there are 2 possible ways of doing it.  One option is to predrill and use pigtails in the footing.  The other is to post install by drilling through the footing into the rock.


I would think wedge anchors would be more reliable because you may not get a clean hole for the epoxy.  Plus, pumping equipment is needed.


Any other thoughts on this would be appreciated.






From: Joe Grill [mailto:jgrill(--nospam--at)]
Sent: Tuesday, July 18, 2006 11:09 AM
To: seaint(--nospam--at)
Subject: RE: Footing Overturning in Rock


Using those pesky little anchors that we have been talking about the last couple of days.


Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying


-----Original Message-----
From: Rich Lewis [mailto:seaint03(--nospam--at)]
Sent: Tuesday, July 18, 2006 9:02 AM
To: seaint(--nospam--at)
Subject: Footing Overturning in Rock


I’m working on the design of a simple spread footing bearing on rock.   The overturning moment due to wind is large requiring a large footing to meet the 0.6*D + 1.0*W load combination.  I was wondering about possible techniques for engaging the rock to help resist overturning and uplift.  Is it feasible to anchor into the rock to do this?  Are there other methods to utilize the dead weight of the rock to help resist overturning?


Thanks for your help.