I agree totally with you, Gerard. The
wall movement indicates failure. The calculations indicate failure. To ignore
failure is folly. I totally agree on getting a soils evaluation, also.
EFP of 45 pcf? I can't say on this one.
We have a geotech on a job now who recommends 56 pcf. I think that's a little
high, but I must defer to his judgment.
Bob Garner, S.E.
From: Gerard Madden,
Sent: Tuesday, February 13, 2007
Subject: Existing Property Line
I was retained to look at an approximately 100 year old unreinforced
concrete gravity retaining wall that is along a shared property line of two
residences. The wall retains about 9 feet of soil and is about 175 feet long.
40 feet of the wall has rotated 9 degrees into the property on the toe side and
the remaining 135 feet has rotated 6-7 degrees. At the worst condition, the top
of the wall overhangs the bottom by 15 inches.
There is no soils report available and I'm recommending complete replacement or
retrofit via. dead man system for the entire wall. I am requiring that a soils
report be generated to establish a design criteria.
Wondering if this seems out of line to any of you? These seem like excessive
movements and rotations and only a matter of time before the wall collapses.
It's service life is up and the wall doesn't appear to have any drainage behind
it, weep holes etc...
I know the wall was initially underdesigned (well, it was probably never
designed, just built) for the height of the soil being retained. It's front
side was built straight while the stem varies from 15" thick at the top to
about 32" 6 feet below (there is one point where I can see the
cross-section fully, but only to 6 feet from T.O. Soil). I suspect the wall was
originally built entirely on the retained side's property but slid into the toe
side property, settled, and rotated. There are large vertical cracks in a
couple of spots, but in general, the wall is intact, but simply rotated and
A quick calc using EFP of 45 psf (low end for bay area soils reports I've seen)
and a base wall thickness of 36" wide without hydrostatic build up yields
safety factors for sliding and overturning around 0.69 and 0.85 respectively,
not close to 1.5 and 2.0 per current codes. With hydrostatic pressure this is
obviously going to be worse.
Needless to say, the owners of the two properties are battling over who should
pay to fix the wall. I'm not getting into that, but simply stating my
professional opinion based on my observations.
I'm confident that my recommendations are valid, but just wondering if any of
you have encountered rotations to this degree (say 6-7 degrees) and felt no
action was required. The owner on the retained soil side had a structural
engineer prepare a drawing addressing only the 40 foot stretch of wall with the
9 degree rotation which is surprising to me.