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FAQs > Slurry walls for
seepage problems in levees.
How are slurry walls used to remedy seepage problems
of levees?
 Since
the 1940s slurry cutoff walls have been used as seepage barriers
to limit the horizontal flow of water and provide added stability
for dams and the foundations on which dams rest. The two most common
types of non-structural slurry walls are referred to as soil-bentonite
(SB) and cement-bentonite (CB). Both types require trenching and
placement of SB or CB backfill to form the cutoff wall. In the SB
method, bentonite-water slurry is poured into the trench during
excavation to provide temporary side wall support. After the trench
is excavated to its required depth, a mixture of soil, bentonite
and water is placed into the trench displacing the bentonite-water
slurry. In the CB method, cement is added to the bentonite-water
slurry just prior to pouring into the trench. In addition to serving
as stabilizing fluid to maintain open trench during excavation,
the CB slurry remains to set up and form the permanent cutoff wall.
For several decades, slurry cutoff walls have been used to control
seepage both through and under dams and levees. It has also been
used as an effective barrier to reduce leakage from ponds. In early
1980s, U.S. Environmental Protection Agency began approving slurry
cutoff walls in waste
management applications to control flow of groundwater at contaminated
sites. With the recent heightened awareness of many inadequate
and high-hazard levees, the technology is often considered for levee
rehabilitation. Several projects have been completed in Sacramento,
CA. One of the levee
stabilizing schemes is listed on the City of West Sacramento website.
Depending on project requirements, levee stabilization may require
the installation of a cutoff wall to control groundwater seepage
and prevent piping failures, adding materials on upstream and downstream
sides to improve stability, and/or raising the levee to increase
capacity.
Parameters usually considered when designing a slurry wall for
levees are permeability, strength and deformability. Strength usually
is not the primary factor and most projects require less than 100
psi compressive strength at 28 days for CB mixtures.
For more technical information on slurry cutoff walls, the following
publications are suggested:
• Cement-Bentonite
Slurry Trench Cutoff Walls (IS227)
• Slurry
Walls: Design, Construction and Quality Control, ASTM STP1129
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