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Re[2]: Sloping Footings

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Former Lurker Now Treasurer Dan,

First, check out the CalTrans Highway Design Manual Section 7-213.4, (2)  (my
version of this section is dated February 1, 1980).  Interestingly, this section
starts out: "For economy and ease of construction..."  They further state that
"The maximum permissible slope for a reinforced concrete retaining wall is 3%." 
This is reduced to 2% for masonry walls.  I would also add that the foundation
has to be level for a crib wall.

I'm not sure what jurisdiction you are working in, but you may also want to take
a look at Section 1806.3 of the 1996 City of Los Angeles Building Code and
Figure 18-I-2 of the City Code.  I have seen this required for modest retaining
walls.

I would consult your Geotechnical Engineer of Record, but in my opinion, it is
not overly conservative to require step footings ( 2 feet step every 10 feet). 
Otherwise, you have a 3-dimensional sliding and overturning problem.  Be careful
of adverse geology.  Some contractors I've worked with in the past prefer the
level working surfaces, in any case.  Sloped footings may not be a cost savings.
 I also concur with prior responses: drainage, drainage, and drainage.

Tom Benson at Lowney Associates, (626) 396-1490

____________________Reply Separator____________________
Subject:    Re: Sloping Footings 
Author: <seaint(--nospam--at)seaint.org>
Date:       6/20/99 12:21 PM

Novak, Dan wrote:
> 
> We are working on an access road/driveway and will require a 5 foot high
> retaining wall. The road slopes in a vertical curve as much as 20%.
> Is there a precedent for the design of a spread footing for a retaining wall
> that is sloping up to 20% in the direction parallel to the wall?  Section
> 1806.4 of the 1997 UBC states that foundations for all buildings where the
> surface of the ground slopes more than 10% shall be level or stepped. Does
> this necessarily apply to retaining walls ?  Do DOT's or one of the
> county road departments have a standard that addresses this question ?
> What are the issues other than sliding parallel to the footing and
> construction difficulties that may effect the foundation?
> Thanks for your input.
> Dan Novak ASL Consulting Engineers  "Former lurker"
> 
1.        Step the footing.  I wouldn't trust construction conditions/methods
to validate a sloped bottom sliding analysis even for a 5ft wall.
2.        Take care to properly drain the system (behind and under the
structure).  If cold climate, weep holes can form ice on the driveway
which is just asking for a lawsuit.
3.        Also, question the 20% slope.  My experience is that over 15% causes
many problems the Owner has to deal with every day.  That kind of design
leads to complaints (or worse).  Make sure the Owner/Client fully
understands the implications of a 20% slope and signs off.

Good luck.

Laurence Oeth, P.E.