METHOD STATEMENT
FOR
CONSTRUCTION OF DIAPHRAGM WALLS
(with BAUER BC Trench Cutter System)
Submitted by
BAUER Maschinen GmbH
2007
BAUER Maschinen GmbH • 86529 Schrobenhausen • Tel. (08252) 97-0
METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
Table of Contents
1
General .................................................................................................................3
2
Description of Equipment ...................................................................................4
2.1
Trench Cutter BC............................................................................................................. 4
2.2
Circulation and desanding equipment.............................................................................. 5
3
Construction Sequence ......................................................................................6
3.1
Guide walls...................................................................................................................... 7
3.2
Pre-excavation ................................................................................................................ 8
3.3
Panel excavation ............................................................................................................. 8
3.3.1
Excavation of primary panel trenches .............................................................................. 9
3.3.2
Excavation of secondary panel trenches and the formation of joints: ............................. 10
3.4
Verticality Control (Recording of Verticality)................................................................... 11
3.5
Installation of Reinforcement ......................................................................................... 12
3.6
Desanding ..................................................................................................................... 13
3.7
Concreting ..................................................................................................................... 14
4
Material Specifications......................................................................................16
4.1
Stabilising fluid .............................................................................................................. 16
4.2
Concrete........................................................................................................................ 18
5
ANNEXES ...........................................................................................................19
5.1
Equipment List............................................................................................................... 19
5.2
Layout of a bentonite treatment plants........................................................................... 20
5.3
Pipeline layout ............................................................................................................... 24
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
1
General
This Method Statement describes the construction method and the sequence of activities required
for the construction of a diaphragm wall. It describes also the main equipment which will be needed
to execute the works.
We emphasize that this Method Statement is a description of events given at the planning stage.
Varying soil conditions or differing site conditions may result in a modification of the construction
methodology. Major modifications will be submitted to the Engineer for approval.
Diaphragm walls are underground structural elements commonly used for retention systems and
permanent foundation walls. They can also be used as deep groundwater barriers.
Diaphragm walls are constructed using the slurry trench technique. The technique involves
excavating a narrow trench that is kept full of an engineered fluid or slurry. The slurry exerts
hydraulic pressure against the trench walls and acts as shoring to prevent collapse. Slurry trench
excavations can be constructed in all types of soil, even below the ground water table.
Specific applications and ground conditions demand the use of hydraulically operated reverse
circulation trench cutters where the excavation technique is by 'cutting' as opposed to 'digging'.
This technique is appropriate for deeper diaphragm walls and walls located in granular materials
and soft rock.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
2
2.1
Description of Equipment
Trench Cutter BC
The trench cutter is an excavating machine that operates on the principles of reverse circulation. It
is made up of a heavy steel frame (1) to the bottom of which are mounted two gear boxes (2).
Cutting wheel drums fitted with a series of teeth are fixed to the gearboxes; they rotate in opposite
directions, break up the soil and mix it with the bentonite suspension (3). As the cutter penetrates,
soil, rock and bentonite are conveyed towards the openings of the
suction box (4). From where they are pumped by a centrifugal pump
(5), located right above the cutter wheels, through the slurry pipe
incorporated in the cutter’s frame, via the mast head into the slurry
conveying system to the desanding plant. Here solid soil and rock
7
particles and liquid bentonite are separated and the latter is pumped
back into the trench.
1
6
The torque output of the cutter wheels in combination with the
weight of the cutter is sufficient to cut into any type of soil and to
crush cobbles, small boulders or weak rock or to overcut concrete
of adjacent panels.
Depending on the soil conditions, different types of cutting teeth can
be deployed, ranging from aggressive teeth for cutting fine-grained
soil to percussive teeth for crushing boulders. In order to protect the
cutter’s gear boxes from excessive dynamic forces when crushing
stones, elastic shock absorbers are located between the cutting
wheel drums and the gear boxes.
The verticality of the trench cutter and thus the trench alignment are
generally measured on two axis by means of two independent
inclinometers (6): the “X”-axis, normal to the trench alignment and
3
the perpendicular “Y”-axis. Data provided by these inclinometers is
processed by the computer on-board the base carrier and displayed
on-line. In this way the operator can monitor continuously and, if
2
necessary, correct the verticality of the cutter. Adjustment of
4
verticality in the two directions is carried out by a system of steering
Fig 1 BAUER Trench Cutter
plates (7). Throughout the excavation process the rig’s operator is
prompted by the machine’s software that calculates its status and
indicates the most appropriate action take. All information can be downloaded on a “Panel report”
that can be printed after completion of each panel and used for QA/QM purposes.
5
The Cutter’s progress can be controlled selectively, in relation to either the rate of penetration (in
soft soils) or the cutter weight (crowd force in hard soils), by using the push buttons on the control
panel. These activate the highly sensitive main winch mounted on the base carrier.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
Fine adjustment of the cutter’s progress, speed of the cutter wheels and pumping volume of the
mud pump is by a series of potentiometers. The control panel monitor shows current operating
modes of the cutter. By switching to different monitor levels, more detailed data can be called up
as required.
2.2
Circulation and desanding equipment
Bentonite slurry is required to stabilise the trench. In addition, when working with the trench cutter,
the slurry is used to convey excavated material out of the trench. Charged slurry is pumped to a
desanding plant, where the solid content of the charged slurry is separated from the liquid fraction
that is pumped back to the trench.
The treatment plant is made up of four essential components:
•
The mixing unit,
An efficient mixing unit mixes bentonite powder with water and pumps it to a holding and hydration
tank where the slurry is kept in motion and aerated for 12 hours before being put to use. This
process is necessary for the bentonite to fully develop its properties of viscosity and thixotropy.
Hydrated bentonite slurry is then transferred by a pump to the main reservoir.
•
The desanding unit
The desanding unit is made up of three items: a central Coarse Screen Separator (Scalping unit)
that removes all particles larger that 8 mm through a vibrating screen; two desanding units that
comprise hydrocyclones, driers, distribution boxes and pumps that separate from the slurry all
particles down to 20 microns. Desanded slurry is then pumped back to the storage reservoir for
reuse.
Fig 2 Bauer Desanding Unit BE 500
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
•
The storage unit
The storage unit can be made up of a series of ponds excavated in the ground, steel tanks stacked
parallel or on top of one other or, if space is at a premium, a series of silos. The layout can have
different configurations to best suit the geometry of the site but it is important, in order to guarantee
continuity in the work that the total capacity of the storage be unit be at least 3 x the volume of one
panel trench.
In the design of storage capacity, consideration should be given to the local geology. If there are
indications of the presence of formations that could lead to a sudden loss of bentonite during
excavation and that could thereby compromise the stability of the trench. The size of the storage
basins should take into account a surplus supply that needs to be used in these emergency
situations.
•
The conveying unit
The conveying unit is made up of a series of pumps, pipes, valves and controls designed to
facilitate conveying bentonite to and from the trench. In the design of the conveying unit account
must be taken of the high volumes of flow of Bentonite to and from the trench:
They can be as high as 500 m3/hr
On return lines, charged slurry can have a solids content higher than 8%
Particles flowing through the lines can be as large as 80 mm.
Account must also be taken of the distance from the furthest panel position to the treatment plant.
The diameter of all pipelines is normally 150 mm (6”). The bentonite return line however, used
during concreting, can be of 100 mm (4”) diameter.
In the design of the conveying unit it is always good practice to include a fresh water supply line to
the trench. This is used principally for cleaning.
The site setup with storage and bentonite treatment areas are shown in ANNEX
3
Construction Sequence
The working sequence for the construction of a diaphragm wall comprises the following key steps:
•
Site preparation, guide wall construction and trench pre- excavation
•
Panel excavation
•
Panel cleaning (desanding)
•
Reinforcement installation
•
Concreting
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
3.1
Guide walls
Guide Walls need to be constructed prior to the diaphragm wall to provide:
•
Guidance to ensure the correct alignment of the pre-excavation.
•
Stability of the upper trench that could be affected by the vertical surcharge induced by
the Cutter and other heavy jobsite traffic adjacent to the trench.
•
Protection against instability of the uppermost layers of soil caused by washing and
fluctuating levels of bentonite slurry during excavation.
•
Prevent collapse of the top of the trench due to equipment loads close to the trench.
•
Support for the vertical loads imposed by the reinforcement cages that are suspended off
the top of the guide wall.
The guide walls are normally constructed as a cast-in-situ reinforced concrete unit.
Typical dimensions are shown below
250
X + 50
250
BRACING EACH 2M
1500
BACKFILLED & COMPACTED
OR LEAN CONCRETE
250
D16 EACH 250
240 KG/CM^2 CONCRETE
BLINDING CONCRETE
100
700
X + 50
700
Fig 3 Typical guide wall system
Firstly, a trench will be excavated with a firm levelled base.
Following the erection and surveying of the shuttering, reinforcement in the form of mesh and
longitudinal starter bars will be placed and the concrete will be poured.
The shutters will generally be removed the following day and may be reused for the next guide wall
section.
It is required to install solid horizontal bracing (e.g. made of wood dia 150 mm, fixed with wedges)
every 2 m to avoid displacement of the guide wall when working with heavy construction
equipment near to the open trench.
The guide wall construction trench shall be backfilled with layers of well compacted soil.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
3.2
Pre-excavation
For the cutter to operate properly the circulation of bentonite must be established before the
machine starts to excavate the trench.
The cutter’s mud pump is located above the cutting wheels and in order to prime this pump it
should be fully submersed in the bentonite fluid. Some pre-excavation of the trench must be
carried out therefore, using other tools, to facilitate priming of the mud pump.
Prior to starting any excavation work it is imperative that existing utilities that may be damaged by
the construction work be locate and if necessary removed or relocate.
Prior to starting the works it is imperative to locate existing utility lines and relocate them if
necessary.
3.3
Panel excavation
Following preparation of the site and construction of the guide walls, excavation of the diaphragm
wall can begin using BC trench cutter. In order to ensure trouble-free excavation and that the
required alignment of the trench is maintained, the cutter should always work within similar
boundaries.
The following sketches illustrate typical applications.
Soil
Soil
Fig 4 Excavation in soil - soil boundaries
Concrete
Concrete
Fig 5 Excavating in concrete- concrete boundaries
Diaphragm wall construction begins with the trench being excavated in discontinuous sections or
“panels” using a BAUER trench cutter BC.
Typically primary single or multiple bite panels are constructed first, followed by the construction of
intermediate secondary or closing panels
Panel excavation is carried out in a predefined sequence to enable the construction of clear joints.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
This is achieved by constructing alternate “primary” panels first, followed by the excavation of the
intermediate “secondary” or “closing” panels.
3.3.1
Excavation of primary panel trenches
The minimum length of one panel is 2.8 m or 3.2 m (determined by the geometry of the machine).
Whenever the soil conditions and/or the geometry of the wall permit, longer, multiple 'bite' primary
panels, consisting of 3 or more consecutive 'bites' can be constructed. (e.g. triple bite with a left
bite 2.8 m - right bite 2.8 m - centre bite 0.5 to 1.5 m = total primary panel length 6.1 to 8 m).
During excavation of the primary panel trenches the level of bentonite slurry within the excavated
trench must be monitored continuously and checked to ensure stability of the open trench.
After reaching the final depth, the verticality of the trench will be re-checked and the bentonite is
usually recycled to ensure it fulfils the specified criteria for concreting
Bite1
Bite3 Bite2
6,1 - 8m
Fig 6 Triple-bite excavation
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
3.3.2
Excavation of secondary panel trenches and the formation of joints:
To ensure continuity of the diaphragm wall, joints between successive panels are formed when
excavating the secondary panel trenches by overcutting into the concreted primaries. The amount
of overcut is variable and can be been determined according to the following guide:
Depth of panel
Amount of overcut "S"
0 - 20 m
150 mm
20 - 40 m
150 - 200 mm
> 40 m
200 mm
The distance between the edges of the adjacent primary panels is designed therefore to leave a
clearance of 2.8 m (or 3.2 m) – 2S m for the excavation of the secondary panel trenches.
Secondary panels are usually “single bite” panels. The BC cutter, that cut a trench 2,80 m (or 3,20
m) long, will cut “S” cm into the concrete of the two adjacent primary panels, resulting in a grooved,
roughened surface of the primary panel concrete.
The construction of secondary panels should not start before 3 to 4 days of completion of the
adjacent primary panels.
In order for a good joint to be formed it is important that the secondary panel concrete comes into
direct contact with clean concrete surfaces of the adjacent primary panels. Care must be taken to
be ensured that no significant pockets of bentonite or lumps of soil adhere to the concrete surface.
It is good practice therefore to perform a brushing
cycle before concreting.
A steel brush attached to the side wall of a chisel is
lowered and raised along the concrete surfaces of
the primary panels, until they are clean.
Fig 7 Brushing tool
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
PRIMARY PANEL
PRIMARY PANEL
1
280cm
3
140cm
2
280cm
700cm
SECONDARY PANEL
OVERCUT LENGTH 20cm
20cm
OVERCUT LENGTH 20cm
1
240cm
20cm
280cm
Fig 8 Sequence primary panels - secondary panels
3.4
Verticality Control (Recording of Verticality)
The verticality of the trench will be measured in the panel axis and perpendicular to the panel axis
by means of two independent inclinometer systems that are mounted on the trench cutter.
The B-Tronic system records the inclination of the
tool in the excavation and correlates it with depth.
Fig 9 Screen display with cutter unit
The onboard computer then processes this
information. A graphical representation of the tool
and its position within the trench can then be
displayed on a monitor inside the operator’s
cabin. A view of the screens as seen by the
operator is shown below. The information as
displayed in real time on the screen assists the
operator in maintaining the verticality of the trench
excavation. In addition to the ongoing
measurement, visual display, and data collection
of verticality while excavating, a "measurement
drive" is conducted after the panel has reached its
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
projected depth. The recorded data of the measurement drive will be stored and printed out as
"Verticality Report", which forms part of the Control records for operation.
3.5
Installation of Reinforcement
Once the excavation of a panel is complete, a prefabricated reinforcement cage is lowered into the
trench to the depth required by the specifications.
Setting benchmarks on the top of the concrete guidewall can avail to place the cage carefully into
the correct place.
The system of overcutting adjacent panels with the trench cutter to form good joints, requires
special caution for the dimensioning and placing of the cages.
A sufficient cover must provided to prevent the machine from accidental cutting into the
reinforcement of an adjacent primary panel.
If the reinforcement cage extends very deeply, it may be necessary to install two vertical steel
beams as temporary “spacers” into the primary trench prior to placing the reinforcement cage.
The beams will be extracted during concreting.
In the design of the reinforcement cage, free slots must be provided for passage of the tremie
pipes (app. 50 x 50 cm) and the cages must be well cross-braced on all faces for rigidity.
2.8
Tremie pipe
(Allow for free area
50 X 50 cm)
SECONDARY PANEL
0.2
0.4
1.5
1.5
Temporary
steel beam
Approx. 7.0m
PRIMARY PANEL
Fig 10 Typical Rebar Cage Layout
It is always preferable, when possible, to lift the reinforcement cage and to place it in the trench in
one piece even if two service cranes and spreader beams need to be used.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
Alternatively the cage may be installed in one or more sections of manageable length. In this case
each successive section of cage is lowered onto the previous one; the two are then connected
together by splicing the longitudinal bars or by other connecting techniques such as welding or the
use of rebar couplers.
Lifting hooks and additional stiffener bars should be
provided as part of the reinforcement cage in order
to facilitate lifting.
After the complete cage is lowered into the trench it
is located at the correct position by suspending it
from top of the guide wall using a series of hooks
welded onto the cage itself.
Spacers need to be mounted to the outside edges
of the cage to ensure the specified concrete cover
is guaranteed throughout the length.
The correct level of the reinforcement cage will be
achieved by suspending it on top of the guide wall
by means of hooks which will be welded to the
reinforcement cage.
Spacers will be attached to the outside of the
reinforcement cage to ensure the concrete cover
required in the specifications. The spacers will be
either sledge-shaped or circular-shaped and will be
manufactured on site of concrete.
Fig 11 Installation of reinforcement cage
3.6
All bar laps, lifting hooks and stiffener bars will be
welded to ensure a rigid reinforcement cage.
Desanding
Prior to concreting, bentonite in the trench is circulated through the desanding plant; alternatively it
may be partly or completely replaced by fresh bentonite so that its characteristics satisfy the
contract requirements. The decision on whether to circulate or to replace the slurry is a function of
the properties of the slurry in the trench - mainly the sand content, the contract specifications that
characterize this material and the availability of fresh bentonite and time.
It is common practice to use the trench cutter itself to replace or recycle the trench slurry. The
machine is kept just off the bottom of the trench and its centrifugal pump is used to pump the slurry
to the treatment plant.
Alternatively a heavy duty submersible pump may be lowered to the bottom of the trench in lieu of
the cutter.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
3.7
Concreting
Concreting a fluid filled trench is carried out using a “Tremie pipe” that introduces fresh concrete to
the bottom of the trench and allows it to rise upwards displacing the fluid in the trench. Concrete
will be supplied to the trench locations by concrete trucks at a rate sufficient to ensure a pouring
rate of about 45 m3/hour, using the tremie pipe method.
The number of tremie pipes will be determined primarily based on the length of the individual panel
to be concreted. For panels up to 4 m length one tremie, for 4 to 7 m two tremies should be used.
Fig 12 Pouring Concrete
One tremie pipe string consists of:
•
1 hopper with lifting rope
•
tremie pipes dia 250 mm in section lengths of 3 - 5 m with male and female connections
•
1 lifting cap and 1 tremie support fork to rest the string on the guide wall
When working with tremie pipes the following precautions should be observed:
•
Joint O-rings must be kept in good order at all times and in conjunction with grease will
ensure adequate water tightness of the joints between successive tubes
•
Before beginning each pour a sacrificial buffer between bentonite and concrete is placed
in the tremie pipe to prevent mixing and segregation of the concrete and bentonite. This
buffer may be made with vermiculite granules or by using a rubber ball or simply a plastic
bag filled with rags.
•
The tremie pipe string is usually positioned and manoeuvred by a service crane.
•
Concrete must be supplied to the trench locations by concrete trucks at a rate sufficient
to ensure a pouring rate of about 25 m3/hour/tremie pipe.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
•
Concrete is then poured directly from the truck mixer into the tremie pipe hopper. During
the concreting operation the bottom of the tremie pipes must be kept immersed in the
fresh mix by a minimum of 3 metres at all times. In order to avoid bentonite inclusions in
the finished wall, the level of the concrete/bentonite interface and the bottom of the tremie
pipe must be monitored to ensure that the difference is always between 3 m and 8 m.
•
When two tremie pipes are used, two concrete trucks are required to start the pour
simultaneously and thus to ensure that no bentonite is trapped and mixed into the
concrete at the bottom of the trench.
•
Before use, tremie pipes shall be clean and well serviced, internally they must be free of
any old and hardened concrete so as to allow for the smooth passage of concrete.
•
Bentonite displaced during concreting is pumped to the treatment plant for desanding and
regeneration. The last 2 m of bentonite in the trench however, i.e. bentonite that is in
contact with fresh concrete and possibly contaminated, is disposed of elsewhere.
•
The trench is normally concreted to the top of guide wall level or at least 30 cm above
final cut-off level. This measure will compensate for segregation or contaminated
concrete near the concrete/bentonite interface and will ensure sound concrete is found at
the cut-off level.
Hopper
Lifting Cap
Support Fork
Tremie Pipe
O-Ring
Seil Rope
Starter Pipe
Pipe Coupling
with Steel Cable
(Standard)
Pipe Connection
with Threads
(Option)
Fig 13 Typical tremie pipe assembly
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
Working sequences in the cutting technique
Pre-excavation
Concreting of the primary
panel
4
4.1
Cutting of primary panel
Cutting of the secondary
panel
Cutting the middle bite
Installation of reinforcement
Installation of reinforcement
Concreting of he secondary
panel
Material Specifications
Stabilising fluid
The trench stabilising fluid is a mixture of bentonite, polymer or a combination of both with water.
Admixtures such as soda may also be included in the mix design to prevent, for example, cement
contamination or flocculation due to salinity of water.
The slurry mix design will be finalized on site following the results obtained from trial mixes.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
A typical bentonite concentration will be 30 - 40 kg of dry bentonite per 1 m3 of slurry.
Dry bentonite or Polymer powder is stored on site. After mixing it thoroughly with water using the
mixer described above, it is pumped to a hydration tank where the slurry is kept in motion and
aerated for 12 hours. This process is necessary for the bentonite to fully develop its properties of
viscosity and thixotropy. It is then pumped to the main storage tanks for use.
During the excavation process the fluid may become diluted or contaminated, it is important
therefore that its properties be checked at regular intervals to ensure consistency in its quality.
The source and properties of the bentonite or polymer to be used shall be provided in the form of
supplier certificates. The certificates will be submitted prior to the commencement of the works for
approval.
The properties of the bentonite should be checked at regular intervals at the trench to ensure
consistent quality of the slurry. For checking the quality of the slurry the following equipment shall
be used:
•
Marsh funnel
•
Mud balance
•
Sand content measuring kit
•
Filter Press
•
Fann Viscometer (or similar)
The following table lists a range of properties of typical bentonite slurry. The values are empirical
and can be used unless different values are given in the project specifications.
Property
to be measured
Test method and
apparatus
API RPI3
Section
Recommended values
slurry pumped to the
trench
slurry in the trench
prior to concreting
Density
Mud balance
1
< 1.30 g/ml
< 1.15 g/ml
Viscosity
Marsh cone
2
30 - 70 seconds
< 90 seconds
Sand content
Sand screen set
4
unlimited (high content
is advantageous in
permeable layers)
<5%
pH
Electrical pH meter
range pH 7 to 14
-
9.5 to 12
9.5 to 12
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
4.2
Concrete
When concreting through Tremie pipes, high slump concrete mixes must be used.
Typical values of slump must be between 150 mm - 200 mm. The mix design is usually finalized
after the performance of trial mixes. Nevertheless a typical mix design for concrete, used in
diaphragm walling, is as follows:
• 28 day cube strength
30 N/mm2
• max. free water/cement ratio
0.50
• workability by slump test
150 mm - 200 mm
• min. cement content
380 kg/m3
• max. aggregate size
20 mm
Additives such as plasticizers or retarders may be included in the mix as required.
On-site sampling and testing of concrete usually consists of taking:
•
Sets of cubes - The amount and frequency of sampling and testing are specified in the
contract specifications.
•
Slump tests - carried out regularly on site to check consistency in the workability of the
concrete.
During the concreting process the actual consumption of concrete is plotted against the theoretical
volume and is included as part of the panel records. This information will enable the identification
of zones of necking or overbreak.
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METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
5
ANNEXES
5.1
Equipment List
The following main items of plant and equipment are needed on site for the construction of a
diaphragm wall:
Nos
1
set
Description
kW
Supplier
Trench Cutter BC on suitable base carrier
450
Bauer
Capacity
Cutting wheels (standard, round shank chisels
or roller bits - depends on conditions)
1
Desanding unit BE 500
122
Bauer
500 m3/h
1
Desanding unit BE 250
60
Bauer
250 m3/h
1
Bentonite Mixer
20
Bauer / local
20 m3/h
1
KBKT pump
110
Bauer
450 m3/h
2-6
Auxiliary pumps
Bauer / local
1
Service crane 60/80 to
300
local
1
Excavator
100
local
Others
150
local
Pipe work for bentonite handling and circulation
Total approx.
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Bauer / local
1300
19
METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
5.2
Layout of a bentonite treatment plants
Typical bentonite handling plants are shown below.
The storage volume is quite substantial and shall be provided in form of earth ponds, tanks or silos.
The storage volume is normally separates in several areas:
•
Swelling basin for hydrating freshly mixed bentonite slurry
•
Concrete bentonite basin - buffer for exchanging slurry prior to concreting
•
Working bentonite basin - for slurry circulation during excavation
•
Waste bentonite basin
BAUER Maschinen GmbH • 86529 Schrobenhausen • Tel. (08252) 97-0
20
Concreting
P3
Concrete truck
Crane
Dry
bentonite
Mixer
Compressor
Generator
Option
Desander
Concrete
bentonite
Concrete Working Working Working Working Fresh
bentonite bentonite bentonite bentonite bentonite bentonite
RB
P4
4"
P1
6"
6"
KBKT
BE250
GS500
BE250
P2
Recyclingcontainer
METHOD STATEMENT
Cutter
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
storage in form of
tanks
Fig.14 storage in form of tanks
BAUER Maschinen GmbH • 86529 Schrobenhausen • Tel. (08252) 97-0
Excavation
21
Concrete truck
Concreting
Excavation
P3
Crane
Cutter
BAUER Maschinen GmbH • 86529 Schrobenhausen • Tel. (08252) 97-0
6"
4"
P4
Mixer
Dry
bentonite
RB
KBKT
SILO
SILO
Concrete
bentonite
BE250
SILO
Compressor
GS500
SILO
BE250
Working
bentonite
SILO
storage in form of silos
Recyclingcontainer
P2
Generator
Waste
bentonite
METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
Fig 15 storage in form of silos
22
P3
Dry
bentonite
Concrete truck
Crane
Mixer
Option
Compressor
RB
Concrete Concrete
bentonite bentonite
container container
Desander
P4
Generator
P5
P5
Working
bentonite
earth tank
Working
bentonite
earth tank
6"
4"
~10"
~10"
6"
6"
KBKT
BE250
GS500
BE250
Recyclingcontainer
METHOD STATEMENT
Cutter
Concreting
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
storage in form
of earth ponds
Fig.16. storage in form of earth ponds
BAUER Maschinen GmbH • 86529 Schrobenhausen • Tel. (08252) 97-0
Excavation
23
METHOD STATEMENT
DIAPHRAGM WALLS (with BAUER BC Trench Cutter)
5.3
Pipeline layout
The basins will be connected with a fixed pipe / pump system to allow a continuous operation.
For circulating the bentonite, a 6” steel pipeline system will be setup between the plant area and
the actual working location.
They will consist of a:
•
6” feeder pipeline to the trench
•
6” return pipeline from the trench
•
4” return pipeline from trench during concreting
BAUER Maschinen GmbH • 86529 Schrobenhausen • Tel. (08252) 97-0
24