Condo Media - July 2017 - 41

We recommend that retaining walls
be inspected four times a year; that is,
before or after each season, as heavy
rains or soil movement due to frost
heaving can have a significant effect
on a retaining wall in a short time.
water table. As irrigation piping is
notorious for leaking, pay attention to
any piping near the top of the retaining
wall. Weep holes are designed to reduce
this increase in hydrostatic forces, but
weep holes can be blocked by debris or
overwhelmed by the quantity of water.
One of the first steps in the inspection
process is to observe the conditions of the
ground surface's upslope of the retaining
wall. Some walls have trench or other
types of drains to intercept the water,
while some ground surfaces are designed
to quickly drain water over or around the
wall before it can enter the ground behind
the wall. If water ponding above the wall
is discovered, this problem must be corrected. Ponding will occur if the ground
settles or is removed due to erosion. If the
surface was paved, cracking in the asphalt
or concrete surface can allow unintended
water to enter the soil.
SURFACE INSPECTIONS
The surface of the retaining wall is the
next and perhaps easiest element to inspect. Wall movement should be noted.
Walls should lean back toward the slope
uphill. If they lean forward or have signs
of bulging in any locations, this could
indicate excess back pressure or failure
in the underlying soils. This could be
serious, so the first time this is noted it
should be brought to the attention of the
facility manager or your engineer.
Timber retaining walls can move or
crack due to both earth movement and
insect attack. Timber wall elements can
also rot with age. Prior to the change in

chemicals put in timber today, walls used
to last 30 years; today we are lucky to get
20. Any type of wall can crack and allow
vegetation matter to grow from either
side. All roots, weeds, or other growth
should be removed when discovered, as
they can apply considerable pressure to
the crack and create localized weakening
of the wall. Wall cracks in concrete surfaces can allow moisture to reach the reinforcing steel, causing excess corrosion,
creating not only internal pressures from
expanding rust but also provide a passage
for freezing to create further deterioration
from expanding freeze/thaw cycles.
Missing wall stones or bricks can also be
an indicator of severe problems developing. These missing elements not only
weaken the structural integrity of the retaining wall, they may also be an indication
of excessive soil pressures that forecast
future wall-bulging, including bowing or
bellying, either vertically or horizontally.
LOADING CONDITIONS
AND MOVEMENT
As the original retaining wall was designed
for specific loading conditions, any
changes in the general proximity to the
wall should be considered. This could
include the placement of a structure or
other heavy mass near the ground surface
at the top of the wall or changes in use of
the land by your upslope neighbor. This
could include a roadway, parking lot, or the
use of road salts or deicers near the wall. It
also includes any changes to the pattern of
surface water drainage such as switching
from a grassy surface to a mulched surface.

One of the more subtle wall failures
is the actual movement of the slope
itself. In some circumstances, it is possible for the hillside to shift or move,
carrying the entire retaining wall with
it without damaging the wall itself.
For this reason, it is important to
document not only the wall but the peripheral areas in the vicinity to ensure
any movement out of the ordinary is
noted and reported. Especially note
any ground movement at the foot of
the retaining wall.
Good observation and site management will go a long way to avoid the hidden cost of retaining wall failures.

n JACK CARR, P.E., RS, LEED-AP,
IS SENIOR VICE PRESIDENT WITH
CRITERIUM-ENGINEERS SERVING
ALL OF NEW ENGLAND.

978.879.3825
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CONDO MEDIA AD 2.25'' Wx 4.625'' T- Full color
July 2017 41

Condo Media - July 2017

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