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DIAPHRAGM WALLS, CUT-OFF WALLS
AND SLURRY WALLS




Bilfinger Berger Spezialtiefbau GmbH
Goldsteinstrasse 114
D-60528 Frankfurt
Phone: +49 -69 6688-345
Fax: +49-69 6688-277
Email: spezialtiefbau@civil.bilfinger.com
www.foundation-engineering.bilfingerberger.com
Diaphragm Walls                                                             Diaphragm wall excavation

Diaphragm walls are concrete or reinforced concrete walls
constructed in slurry-supported, open trenches below existing
ground. Concrete is placed using the Tremie installation method or          Excavation pit retained by tied
by installing pre-cast concrete panels (known as a pre-cast                 back diaphragm wall and partially
diaphragm wall). Diaphragm walls can be constructed to depths of            braced by cast-in-place building
100 meters and to widths of 0.45 to 1.50 meters.                            floor slab.

Diaphragm wall construction methods are relatively quiet and cause
little or no vibration. Therefore, they are especially suitable for civil
engineering projects in densely-populated inner city areas.                 Excavation pit retained by
                                                                            diaphragm wall and bracing
Due to their ability to keep deformation low and provide low water
permeability, diaphragm walls are also used to retain excavation
pits in the direct vicinity of existing structures.
If there is a deep excavation pit at the edge of an existing structure
and groundwater is present, diaphragm walls are often used as the
most technically and economically favorable option. They can be
used for temporary support or as load-bearing elements of the final
building. Diaphragm walls can be combined with any anchor and
bracing system.
Diaphragm wall panels are also used in deep, load-bearing soil
layers as foundation elements to carry concentrated structural load
in the same way as large drilled piles do. These foundation
elements are known as "Barrettes".
If diaphragm are socketed into impermeable soil layers of sufficient      Diaphragm wall excavation using
thickness or if they are combined with seal slabs (grout injection or     hydraulic cutter disk and grab
tremie concrete slabs) almost waterproof excavation pits are              excavation
created. After reducing the initial groundwater level within the
excavation, only small amounts of residual water will penetrate.
Diaphragm Wall construction using grab excavation and                     Guide wall
removable Stop-End Pipes
• Preliminary excavation to 1.0 - 1.5 meters below ground
  elevation to install guide walls                                        Diaphragm wall chisel
• Prior to diaphragm wall excavation, cast-in-place or pre-cast
  concrete guide walls are placed. These braced guide walls
  stabilize the soil in the upper diaphragm level and provide a stable
  guide-way for the grab. In addition, they also support the
  diaphragm wall reinforcement and provide sufficient bearing for
  the hydraulic jacking system to remove the Stop-End Pipes. The
  space between both guide walls serves as a storage space for the
  stabilizing fluid.
• Lamella excavation Using hydraulic grabs with clam shell sizes
  of 2.8, 3.4 or 4.2 meters, single diaphragm panels can be
  excavated down to tip elevation. To avoid collapsing ground,
  trixotropic stabilizing fluids (Bentonite slurry = clay/water slurry)
  are pumped into the excavated panel. Depending on ground
  condition and geotechnical design, several single panels can be
  combined to one large lamella. Hard soil, rock or obstructions can
  be removed using chisels in addition.
• Stop End Pipe Installation. To separate the single concreting         Diaphragm wall reinforcing cage
  phases, stop-end pipes are installed at both panel fronts. These      with block-out
  have the same diameter as the panel’s wall thickness and are
  removed after initial concrete setting. The remaining semicircular
  joint provides a very good interlock between the individual
  concrete panels.                                                      Stop-end pipe with hydraulic pipe
                                                                        extractors
• Slurry Refreshing.
• Placing of Rebar Cage
• Concrete Placing by Tremie Method. Simultaneously with
  placing concrete, slurry is pumped from the panel to be refreshed     Flat steel joint element
  and re-used in the next panel excavation. Since the slurry is
  replaced by concrete, this method is called “Double-Phase
  Method”.
• Removal of Stop -End Pipes after concrete setting using
  hydraulic pipe extractors.
Diaphragm Wall Joint Design
• There are three (3) types of joint design used for diaphragm walls
  constructed by the grab excavation method
• Steel stop-end pipes, which are removed before the concrete has
  set completely (as mentioned before). Concrete seeped around
  the stop-end pipes can be safely removed by the use of chisels.
• Pre-cast reinforced concrete panels, which remain in the panels
  as permanent stop-ends (high weight, twice the number of joints).
  Seeping concrete can not be removed safely.
• Steel joint element. This flat steel panel element contains one or
  two elastic joint tapes, which remain in the setting concrete after
  the joint element has been removed. Removal of the element can
  only take place after the adjacent panel was completely
  excavated.
If diaphragm walls are constructed using the hydro-cutter               Concrete placement at a
technique, stop- end pipes do not need to be installed. After the       diaphragm wall panel
primary panel set sufficiently, the secondary panel excavation will
slightly cut into the fresh concrete to ensure a tight overlap during
the concrete placement.
                                                                        Two phase construction using the
                                                                        alternating method
Excavation
Double rope grabs as well as grabs guided by telescoping Kelly
bars are commonly used for excavation in soils. Hydro-cutters can
be employed for rock as well as soft soil excavations. They             Hydro-cutter head
continuously cut into one panel by sucking the soil-bentonite slurry
at the cutter head while replacing it with fresh bentonite at the
panel’s top.

Construction sequence
Two different construction techniques, the alternating method (or
Pilgrim) and the continuous method can be distinguished for
excavation. During the alternating method, only primary panels will
be placed leaving out the following secondary panels. Following the
first primary panels, gaps will be closed by the adjacent secondary
panels. Primary and secondary panels will have different sizes due
to the use of stop end pipes.
During the continuous excavation method (Endless Panel), all the
panels are excavated in one continuous process. Therefore they all
have the same size.
Cut-off Walls                                                          Cut-off wall applications

Cut-off walls are vertical slurry walls with very low water
permeability to minimize the ground water flow.
In contrast to the known load-bearing, impermeable retaining walls     Cut-off wall Rostock,
such as:                                                               Warnowquerung

• Concrete secant pile walls
• Reinforced two-phase diaphragm walls
• Sheet pile walls                                                     Cut-off wall site set up

are cut-off walls mostly without any load-bearing function.
The following cut-off wall types can be distinguished:
• Cut-off walls constructed using diaphragm wall techniques
• Secant pile walls from concrete of slurry
• Thin slurry walls
• Injection walls
• Jet-Grouting walls
• Freezing walls
They can be used as:
• Cut-off walls underneath water dams with core seals in areas of
  permeable soils to socket into lower impermeable layers to
  prevent undercurrent
• Cut-off walls for “watertight” excavation pits outside of the
  load-bearing retaining structure to minimize water inflow into the
  pit
• Cut-off walls to enclose brown fields and contaminated areas with
  penetration into lower impermeable soil layers
Cut-off walls constructed using diaphragm wall techniques                   Slurry wall excavation, DW
                                                                            Rostock, Warnowquerung
If slurry walls are intended to act as cut-off walls without any load
bearing function, a mixture of water, bentonite, cement and maybe
filler can be used.
This slurry remains in the excavated panel and hydrates. It also            Installation of plastic liner sheet,
remains as a plastic seal, so that the wall can follow small                combination cut-off Wall, Central
displacements in the soil without cracking. Since the slurry remains        Waste Dump, Huenxe
in the panel, this is called the Single-Phase technique.
After completion of the guide wall, the excavation proceeds with:
                                                                            Cut-off Wallh head cover
• One long-boom excavator (max. depth of 10m)
• Or by the use of slurry wall grabs or hydro-cutters
Using the single-phase technique, panel depth is limited due to the
relatively short time from placing and setting of the suspension.
In deeper panels, the Two-Phase technique is used to construct a
slurry wall. Construction is similar to the cast in-situ diaphragm wall
installation. After completion of the panel’s excavation, the actual
sealant slurry will replace the stabilizing bentonite fluid. This sealant
has to be placed using the slurry-displacement or tremie method
and needs to have a
0.75 to/m³ higher unit weight than the bentonite slurry to replace it.
To improve permeability and contaminant resistance, combination
cut-off walls can be installed using the Single-Phase system. Sheet
piles or plastic liner sheets can be installed within a
bentonite-cement-slurry wall.
Cut-off walls with embedded sheet piles or structural beams being        Cut-off wall with embedded sheet
constructed using the single phase method can also be used as            pile wall as retaining wall for an
"water- tight" excavation pits.                                          excavation pit, Salzufer, Berlin

In the process the sheet piles or beams act as load transferring
elements and will extend to required depth below the excavation pit.
The Cut-off wall as sealing element will only penetrate the artificial   Cut-off wall with embedded
seal slab or reach down to the natural impermeable soil layer.           H-beam wall as retaining wall for
                                                                         an excavation pit, TG Seestern,
Sheet pile or beam walls can be tied back.                               Duesseldorf




                                                                         “Watertight” excavation pit
Thin Slurry Walls                                                       Construction of a vibrated thin
                                                                        slurry wall, Doemitz
Thin slurry walls also can act as vertical cut-off walls to retain
horizontal groundwater flow.
In contrast to cut-off walls constructed using the diaphragm wall
technique (replacing the soil by slurry sealant), thin slurry walls     Vibro-beam
displace the soils using a vibrated steel profile. During the
extraction process, sealants are injected into the created cavities.
Drivable soils, such as sands and gravels, are required for this        Thin vibro slurry wall
installation method. The created slurry wall thickness depends on
the shape of the steel profile used and the soil conditions.
Thickness varies between 5 cm in sands and 20 cm in gravel. In
combination with high-pressure jet grouting, wall thickness of up to
30 cm can be achieved.
A continuous wall is created by overlapping single penetration
elements installed one after another by the vibrated steel profile. A
guide plate attached at the beam`s flange is running down the
already completed web of the previous panel. This ensures the
correct overlap to the previous panel.

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Diaphragm walls

  • 1. DIAPHRAGM WALLS, CUT-OFF WALLS AND SLURRY WALLS Bilfinger Berger Spezialtiefbau GmbH Goldsteinstrasse 114 D-60528 Frankfurt Phone: +49 -69 6688-345 Fax: +49-69 6688-277 Email: spezialtiefbau@civil.bilfinger.com www.foundation-engineering.bilfingerberger.com
  • 2. Diaphragm Walls Diaphragm wall excavation Diaphragm walls are concrete or reinforced concrete walls constructed in slurry-supported, open trenches below existing ground. Concrete is placed using the Tremie installation method or Excavation pit retained by tied by installing pre-cast concrete panels (known as a pre-cast back diaphragm wall and partially diaphragm wall). Diaphragm walls can be constructed to depths of braced by cast-in-place building 100 meters and to widths of 0.45 to 1.50 meters. floor slab. Diaphragm wall construction methods are relatively quiet and cause little or no vibration. Therefore, they are especially suitable for civil engineering projects in densely-populated inner city areas. Excavation pit retained by diaphragm wall and bracing Due to their ability to keep deformation low and provide low water permeability, diaphragm walls are also used to retain excavation pits in the direct vicinity of existing structures. If there is a deep excavation pit at the edge of an existing structure and groundwater is present, diaphragm walls are often used as the most technically and economically favorable option. They can be used for temporary support or as load-bearing elements of the final building. Diaphragm walls can be combined with any anchor and bracing system. Diaphragm wall panels are also used in deep, load-bearing soil layers as foundation elements to carry concentrated structural load in the same way as large drilled piles do. These foundation elements are known as "Barrettes".
  • 3. If diaphragm are socketed into impermeable soil layers of sufficient Diaphragm wall excavation using thickness or if they are combined with seal slabs (grout injection or hydraulic cutter disk and grab tremie concrete slabs) almost waterproof excavation pits are excavation created. After reducing the initial groundwater level within the excavation, only small amounts of residual water will penetrate. Diaphragm Wall construction using grab excavation and Guide wall removable Stop-End Pipes • Preliminary excavation to 1.0 - 1.5 meters below ground elevation to install guide walls Diaphragm wall chisel • Prior to diaphragm wall excavation, cast-in-place or pre-cast concrete guide walls are placed. These braced guide walls stabilize the soil in the upper diaphragm level and provide a stable guide-way for the grab. In addition, they also support the diaphragm wall reinforcement and provide sufficient bearing for the hydraulic jacking system to remove the Stop-End Pipes. The space between both guide walls serves as a storage space for the stabilizing fluid. • Lamella excavation Using hydraulic grabs with clam shell sizes of 2.8, 3.4 or 4.2 meters, single diaphragm panels can be excavated down to tip elevation. To avoid collapsing ground, trixotropic stabilizing fluids (Bentonite slurry = clay/water slurry) are pumped into the excavated panel. Depending on ground condition and geotechnical design, several single panels can be combined to one large lamella. Hard soil, rock or obstructions can be removed using chisels in addition.
  • 4. • Stop End Pipe Installation. To separate the single concreting Diaphragm wall reinforcing cage phases, stop-end pipes are installed at both panel fronts. These with block-out have the same diameter as the panel’s wall thickness and are removed after initial concrete setting. The remaining semicircular joint provides a very good interlock between the individual concrete panels. Stop-end pipe with hydraulic pipe extractors • Slurry Refreshing. • Placing of Rebar Cage • Concrete Placing by Tremie Method. Simultaneously with placing concrete, slurry is pumped from the panel to be refreshed Flat steel joint element and re-used in the next panel excavation. Since the slurry is replaced by concrete, this method is called “Double-Phase Method”. • Removal of Stop -End Pipes after concrete setting using hydraulic pipe extractors. Diaphragm Wall Joint Design • There are three (3) types of joint design used for diaphragm walls constructed by the grab excavation method • Steel stop-end pipes, which are removed before the concrete has set completely (as mentioned before). Concrete seeped around the stop-end pipes can be safely removed by the use of chisels. • Pre-cast reinforced concrete panels, which remain in the panels as permanent stop-ends (high weight, twice the number of joints). Seeping concrete can not be removed safely. • Steel joint element. This flat steel panel element contains one or two elastic joint tapes, which remain in the setting concrete after the joint element has been removed. Removal of the element can only take place after the adjacent panel was completely excavated.
  • 5. If diaphragm walls are constructed using the hydro-cutter Concrete placement at a technique, stop- end pipes do not need to be installed. After the diaphragm wall panel primary panel set sufficiently, the secondary panel excavation will slightly cut into the fresh concrete to ensure a tight overlap during the concrete placement. Two phase construction using the alternating method Excavation Double rope grabs as well as grabs guided by telescoping Kelly bars are commonly used for excavation in soils. Hydro-cutters can be employed for rock as well as soft soil excavations. They Hydro-cutter head continuously cut into one panel by sucking the soil-bentonite slurry at the cutter head while replacing it with fresh bentonite at the panel’s top. Construction sequence Two different construction techniques, the alternating method (or Pilgrim) and the continuous method can be distinguished for excavation. During the alternating method, only primary panels will be placed leaving out the following secondary panels. Following the first primary panels, gaps will be closed by the adjacent secondary panels. Primary and secondary panels will have different sizes due to the use of stop end pipes. During the continuous excavation method (Endless Panel), all the panels are excavated in one continuous process. Therefore they all have the same size.
  • 6. Cut-off Walls Cut-off wall applications Cut-off walls are vertical slurry walls with very low water permeability to minimize the ground water flow. In contrast to the known load-bearing, impermeable retaining walls Cut-off wall Rostock, such as: Warnowquerung • Concrete secant pile walls • Reinforced two-phase diaphragm walls • Sheet pile walls Cut-off wall site set up are cut-off walls mostly without any load-bearing function. The following cut-off wall types can be distinguished: • Cut-off walls constructed using diaphragm wall techniques • Secant pile walls from concrete of slurry • Thin slurry walls • Injection walls • Jet-Grouting walls • Freezing walls They can be used as: • Cut-off walls underneath water dams with core seals in areas of permeable soils to socket into lower impermeable layers to prevent undercurrent • Cut-off walls for “watertight” excavation pits outside of the load-bearing retaining structure to minimize water inflow into the pit • Cut-off walls to enclose brown fields and contaminated areas with penetration into lower impermeable soil layers
  • 7. Cut-off walls constructed using diaphragm wall techniques Slurry wall excavation, DW Rostock, Warnowquerung If slurry walls are intended to act as cut-off walls without any load bearing function, a mixture of water, bentonite, cement and maybe filler can be used. This slurry remains in the excavated panel and hydrates. It also Installation of plastic liner sheet, remains as a plastic seal, so that the wall can follow small combination cut-off Wall, Central displacements in the soil without cracking. Since the slurry remains Waste Dump, Huenxe in the panel, this is called the Single-Phase technique. After completion of the guide wall, the excavation proceeds with: Cut-off Wallh head cover • One long-boom excavator (max. depth of 10m) • Or by the use of slurry wall grabs or hydro-cutters Using the single-phase technique, panel depth is limited due to the relatively short time from placing and setting of the suspension. In deeper panels, the Two-Phase technique is used to construct a slurry wall. Construction is similar to the cast in-situ diaphragm wall installation. After completion of the panel’s excavation, the actual sealant slurry will replace the stabilizing bentonite fluid. This sealant has to be placed using the slurry-displacement or tremie method and needs to have a 0.75 to/m³ higher unit weight than the bentonite slurry to replace it. To improve permeability and contaminant resistance, combination cut-off walls can be installed using the Single-Phase system. Sheet piles or plastic liner sheets can be installed within a bentonite-cement-slurry wall.
  • 8. Cut-off walls with embedded sheet piles or structural beams being Cut-off wall with embedded sheet constructed using the single phase method can also be used as pile wall as retaining wall for an "water- tight" excavation pits. excavation pit, Salzufer, Berlin In the process the sheet piles or beams act as load transferring elements and will extend to required depth below the excavation pit. The Cut-off wall as sealing element will only penetrate the artificial Cut-off wall with embedded seal slab or reach down to the natural impermeable soil layer. H-beam wall as retaining wall for an excavation pit, TG Seestern, Sheet pile or beam walls can be tied back. Duesseldorf “Watertight” excavation pit
  • 9. Thin Slurry Walls Construction of a vibrated thin slurry wall, Doemitz Thin slurry walls also can act as vertical cut-off walls to retain horizontal groundwater flow. In contrast to cut-off walls constructed using the diaphragm wall technique (replacing the soil by slurry sealant), thin slurry walls Vibro-beam displace the soils using a vibrated steel profile. During the extraction process, sealants are injected into the created cavities. Drivable soils, such as sands and gravels, are required for this Thin vibro slurry wall installation method. The created slurry wall thickness depends on the shape of the steel profile used and the soil conditions. Thickness varies between 5 cm in sands and 20 cm in gravel. In combination with high-pressure jet grouting, wall thickness of up to 30 cm can be achieved. A continuous wall is created by overlapping single penetration elements installed one after another by the vibrated steel profile. A guide plate attached at the beam`s flange is running down the already completed web of the previous panel. This ensures the correct overlap to the previous panel.