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Slurry Walls
Slurry walls are typically installed to provide temporary and permanent
perimeter earth support for deep underground structures, such as buildings
parking garages, tunnels and access shafts. They also provide permanent
water cutoff underneath dams. Slurry wall foundations are most appropriate
where space is limited (urban areas), where adjacent shallow foundations
need rigid support and where a high groundwater table is present. They
are most cost effective when they are used as both the temporary earth
support system and the permanent walls for the underground structure.
Slurry Walls are constructed in individual panels using specially designed
clamshell grabs to excavate a trench for each panel. The panels are typically
2’ to 4’ wide, 10’ to 25’ long and can reach depths
in excess of 150 feet. The trench excavation is stabilized by a bentonite
slurry, hence the term “slurry wall”, which is continuously
fed into the trench as the excavation progresses. When the required panel
depth is attained, pre-assembled reinforcing steel cages are placed in
the slurry filled excavation and concrete is poured through one or more
tremie pipes, thereby displacing the slurry. When all adjoining panels
are completed, they form the perimeter structural wall of the specific
underground structure.
Soldier Pile Tremie Concrete (SPTC) Slurry Walls
SPTC slurry walls are similar to conventionally reinforced concrete slurry
walls except that wall reinforcement is provided by structural steel columns
instead of reinforcing steel bars.
Load Bearing Elements (LBEs)
These are deep foundation elements, extended into subsurface bearing layers,
constructed with the same slurry trench method. They are independent structural
elements that support the loads imposed by the columns of the superstructure
and are used most often as part of the “top-down” building
construction method. “Top-down” construction, whereby the
building superstructure and below ground levels are constructed simultaneously,
is used to accelerate a project construction schedule and to minimize
the lateral movements of the underground perimeter wall during the construction
phase.
Slurry Trenches
Slurry trench cutoff walls are used to provide an impermeable barrier
in a variety of environmental applications, to prevent the contamination
of the surrounding water table by the migration of leachates. Because
of their plastic nature, slurry trench cutoff walls are also used underneath
earthen dams and levees embankments. The slurry trench is constructed
by excavating a 30” to 48” wide trench under bentonite slurry.
The trench is typically keyed into an impermeable underground soil layer
and is backfilled with a mixture of soil and bentonite, cement and bentonite
or soil, cement and bentonite.
Drilled Shafts
Drilled shafts, or caissons, are deep reinforced concrete foundation elements
constructed with a rotary drill rig. They are used to provide support
for column loads of buildings, piers of bridges, or other structures.