30 Jun 96
It is difficult to key steel sheet pile into hard rock,
and keys should preferably be made in clay.
(2) Applicability. The major advantage of using
sheet piling is that no excavation is required. The
disadvantages are the lack of an effective seal of the
pile connections and problems with pile corrosion.
Sheet piles are typically driven in soils that are
loosely packed and predominately sand and gravel in
nature. Piling longevity depends on groundwater
characteristics. For steel piles, pH is of particular
importance. If the pH of the groundwater is in the
range of 5.8 to 7.8, sheet piles can last up to
40 years; however, a pH as low as 2.3 can shorten
Figure 3. Vibratory beam wall-plan view
the lifetime to 7 years or less.
(2) Applicability. The VBI method is best suited
for areas with flat topography and where loose gran-
ular soils are present. Beam penetration is difficult in
(1) Description. In general, grouting is the injec-
stiff clays and rocky soils. The major advantage of
tion of one of a variety of special grouts into soil or
the VBI method over conventional slurry wall sys-
rock, thus greatly decreasing the soil's permeability.
tems is that no excavation of site soils is required,
The injection process involves drilling holes to the
thus creating a safer work environment for site work-
desired depth and injecting grout under pressure by
ers during installation. However, because a relatively
using special equipment. To produce a curtain wall,
thin wall is produced by the VBI method, it is not
a line of holes is drilled in single or double staggered
recommended as a primary barrier for contaminated
rows and grouting is then accomplished. The spacing
of the injection holes is site specific, depending on
continuity, as the tip location of the beam may vary,
site soil characteristics, and is determined by the
especially during deep penetrations. It may be diffi-
penetration radius of the grout out from the holes.
cult to determine when a key layer has been reached
To form a continuous wall, grout injected from adja-
as well. VBI walls should be considered for use in
cent holes should touch along the entire depth of the
conjunction with a groundwater removal system or
hole. When carried out properly, this process can
for diverting clean groundwater around a contamin-
produce a curtain or wall that can be an effective
Sheet pile walls.
(2) Applicability. In general, grout curtain walls
are expensive and may not produce acceptable results
(1) Description. Interlocking sections of steel
sheet pile are driven to a predetermined depth and
Because of this, pressure grouting is used primarily to
may key into a subsurface aquiclude consisting of
seal voids in porous or fractured rock, such as below
clay or another relatively impermeable horizon. Steel
a slurry wall installation.
sheet pile cutoff walls are considered to be a some-
what permeable groundwater barrier. Each section
Deep soil mixing.
interlocks with an adjacent section. The connection
between sections may initially be a pathway for
(1) Description. Deep soil mixing has been used
groundwater migration. This leakage may be reduced
to install vertical barriers. An auger is rotated into
naturally with time as fines are trapped in the connec-
the soil while injecting various slurries, thus creating
tion. If the piles are driven in material with little or
a "column" of low-permeability soil. A continuous
no fines, the connections may never completely seal.
wall is thus created by overlapping the columns of
Leakage in joints may also be sealed artificially by
being filled with impermeable material. Various
sheet configurations are available in varying weights.