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Dog Urine vs. Concrete Wall

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Fellow engineers,

        Nineteen years ago I designed an L shaped cantilever retaining
wall along the back alley of a residential property.  The high side of
the earth backfill is on top of the footing, about five feet higher than
the low side, and on the residence side of the wall.  Sulphate test at
the time indicated that Type 1 portland cement was satisfactory for this
use.  Granular backfill with proper drains was used behind the retaining
wall; but the native soil in the area is silty clay.  General surface
drainage is from the residence toward the retaining wall (at a very
gentle slope).  Average annual precipitation in Calgary is about 17" per

        A portion of the wall about 20" long is now leaning out (5" of
movement observed).  The concrete generally appears to be in very good
condition.  My interpretation of this movement is that the dowels
connecting the footing to the wall may have rusted through.

        Subsequent investigation reveals that the same family has owned
the property for the entire nineteen years and that they have always
owned two large dogs.  Furthermore, the dogs use the area immediately
behind the retaining wall as their bathroom.  The ground surface for the
first 8 to 10 feet from the retaining wall is washed smooth gravel (for
the dogs) with the remainder of the 30 feet (more or less) to the house
being ordinary lawn grass.  Lawn watering is generally required in
Calgary with the general recommendations being not more than watering
plus rain to total 1" per week.  Any excess would probably be absorbed
into the ground in the area used by the dogs.

        My expected solution to the problem is to install three drilled
soil anchors through the retaining wall and into the undisturbed native
soil behind the backfill and connected to a hollow structural on the
face of the wall with epoxy coated or galvanized ties (possibly with an
extra thickness for corrosion allowance).

        Does anyone have any other ideas or information?  Am I way off
base with my dog urine speculation?  I have never encountered this
problem before.

        Thank you for any help you may be able to give.


H. Daryl Richardson

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