the washington post
.
thursday, august
22
,
2019
MD
2
Home
BY JEANNE HUBER
Q: My beautiful stone retaining
wall has sprung leaks during
these recent rainstorms. How
can I fix the problem?
RockvilleA: Your wall is probably just
fine. If it were a leakproof dam
without another route for the
water to escape, you would have
a bigger problem.
Retaining walls like yours
need to hold back soil as well as
the pressure that develops
within it as the ground becomes
saturated after heavy storms.
The water dribbling through is
relieving pressure that might
otherwise cause the wall to
buckle out and collapse and the
soil behind the wall to slump
down.
A couple of landscaping
professionals who build
retaining walls looked at the
picture you sent. They disagreed
on how they think the wall is
built, but both said it appears
you don’t need to worry as long
as sections of the wall beyond
the picture aren’t bulging out.
“The wall shown in the
picture is a dry stacked stone
wall,” Krisjan Berzins, president
and chief executive of
Kingstowne Lawn & Landscape
in Alexandria (703-921-9200;
kingstownelawn.com), wrote in
an email. This means that below
the top course, where the picture
clearly shows mortar, the stones
are just stacked on top of each
other in a way that uses their
weight and gravity to keep them
in place. “It is the natural
irregularities in the stone that
leave small gaps between the
stones, allowing water to trickle
through during periods of heavy
rainfall or soil saturation,”
Berzins said. “Seeing water
trickle through a dry stackedstone wall, such as the one
pictured, is a good thing. This
means that the wall system is
functioning properly.” If thewater couldn’t dribble out,
hydrostatic pressure would
build up behind the wall.
“Hydrostatic pressure buildup
behind a retaining wall is
precisely what causes wall
failure or collapse.”
A representative from
Lifetime Stones (571-436-0370;
lifetimestones.com), a company
in Silver Spring that offers a full
suite of landscaping services,
including construction and
repair of retaining walls, looked
at the picture you sent and
concluded the stones appear to
be mortared together all the way
down, not just in the top layer.
But mortar degrades over time,
he said, and it becomes more
like sand, allowing water to seep
through. As long as the wall
itself isn’t bulging out, this
shouldn’t be a problem.
A mortared stone retaining
wall, as well as those made ofconcrete or mortared blocks,
needs an extensive drainage
system behind the wall to keep
hydrostatic pressure from
causing the wall to collapse. If
your wall is mortared, it
probably does have a drainage
system or it wouldn’t have
survived earlier storms. The
system might have become
overwhelmed by recent storms,
or the mortar might now be
degraded enough so water flows
more easily though the wall than
through the initial drainage
system.
If the wall is leaning, however,that would be cause for concern.
In that case, you should call a
landscaping professional who
installs retaining walls and ask
for an evaluation. If your wall is
leaning, Lifetime Stones might
charge $3,000 to $5,000 to
repair it, depending on the
length of the wall.
The risk of collapse from the
pressure of waterlogged soil is
high enough that heavy-duty
retaining walls need to be
designed by professionals.
Montgomery County requires a
permit and professional design
for any retaining wall more than
four feet high. And if the soil
being retained has something on
it, such as a car or shed, the limit
without professional design and
a permit is two feet.
If you were building the wall
from scratch, you could build in
a way to direct the water down
behind the wall and into a pipe
that would carry it to a lower
spot in your yard. You would
need perforated pipe at the base
of the wall, with the holes in the
pipe angled down to keep it
from clogging with dirt. This
pipe would need to slope toward
one or both sides of the wall and
might need to connect to solid
pipe to get the water to a place
where it could empty out
without causing a problem.
Above the perforated pipe,
you would add gravel to fill the
gap between the wall and the
soil. Spaces between gravel
pieces would give the water a
place to flow. Four inches or so
near the top of the wall, where
you want to transition from
gravel to soil so you can grow
lawn or other plants, you would
cover the gravel with geotextile
fabric (also known as
landscaping fabric) and tuck it
behind the gravel fill. This would
help keep soil from running into
the gravel layer and clogging the
spaces.
When retaining walls are built
of solid materials, such as
concrete or mortared stones or
blocks, there is usually also a
waterproofing membrane
against the back of the wall and
short pieces of pipe slanted
downhill through the front of
the wall to act as weep holes
where any water that collects in
the soil can make its way out
without pushing the wall over.
Your wall already has weep
holes — the spaces between the
stones. Have a problem in your home?
Send questions to
[email protected]. Put “How
To” in the subject line, tell us where
you live and try to include a photo.HOW TO
Don’t worry about your leaking retaining wall — it’s a good thing
Columnists:
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LOCAL LIVING
READER PHOTORetaining walls like the one
above hold back soil and the
pressure that builds in it after
heavy storms. The water
leaking is relieving pressure
that could otherwise cause the
wall to collapse.