I have been asked to
design a replacement for a retaining wall that has failed due to rotting of
the wood posts after some 31 years. This sounds simple enough; just
install new posts between the existing and replace the planking as
required; however, as they say, the devil is in the
The original wall is
from 3 to 7 feet high (from grade) and located on the property line between
two houses each of which are set back about 4 to 5 feet from the
property line. It was apparently build by a developer who had several
such walls to build. The building procedure appears to have been to
excavate a trench about 4 feet wide, build the retaining wall like a fence ,
then fill the trench in with concrete forming a footing 4 feet wide by 1.5
feet thick mainly under the fill on the low side of the wall.
Alternatively, the posts could have been cast into the wet concrete during
the pour; at this time I can not tell the difference.
The original posts
are 6" by 6" actual dimension (not nominal 6x6 timber). The
design works (marginally) for select structural D. fir for strength of
posts (based on 1970 allowables) and overturning based on 1.5 safety
factor and the dimensions stated based on dimensions observed; but it does
not work for current code values.
The contractor is
prepared to build a cantilevered concrete wall utilizing the existing
footing (for extra cost, of course). He does not want to remove the
existing footing; he believes this to be the most expensive and time
consuming solution of all.
Given that both
owners are retired (hence cost is important), and only the middle half of
the entire retaining wall needs replacing, is there a practical way to
connect new 8x8 posts to the existing footing in order to recreate the wood