Download - Top Down Method of Construction
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TOP DOWN METHOD OF
CONSTRUCTION
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TOP DOWN METHOD OFCONSTRUCTION
Top Down Method of excavation adopted for the project as deep
excavation was to be carried out very near to existing buildings.
The top-down construction method enables work to be
undertaken above ground while excavating underground.Not only does this method shorten the construction schedulebut it also minimises associated construction impacts on thecommunity.
Service Corridor, being made in Middle Circle of Connaught Place
is a tunnel of box section of size (6.3 x 7 mtrs) which is being builtby the help of this method.
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Introduction
Diaphragm Wall is generally reinforcedconcrete wall constructed in the groundusing Underslurry Technique which was
developed in Europe. The technique involves excavating a
narrow trench that is kept full of anengineered fluid of slurry.
Walls of thickness between 300 to 1200mmcan be formed up to a depth of 45 metres.
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STEPS OF TOP DOWNMETHOD
Identification of Existing Utilities
Shifting of Utilities & Making of Guide Wall
Boring for Diaphragm Wall up to the required depth
Lowering of R/F cage in the Bored Area
Concreting of the Diaphragm Wall Panel
Excavation & Chipping of Concrete up to the cut-off level
RCC Top Slab for the Service Tunnel
Excavation up to the Bottom Slab
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Identification of ExistingUtilities
Making of Pre-trench across the
road at regular intervals to identify
the utilities running along the
Proposed Service Tunnel
After the utilities were identified,
methodology for shifting of these
utilities were finalized
Pre Trench showing the existing utilities
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Shifting of Utilities & Making of GuideWall
The identified utilities were diverted
temporarily so as to keep the
utilities running & also to make a
guide wall for the boring
A Guide Wall was constructed for a
depth of 1.6 m along the alignment
of Service Corridor to assist in
boring for Diaphragm Wall & to shift
any unforeseen utilities which are
layed across the road & have not
been identified in the pre-trench
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Boring for Diaphragm Wall
Boring done up to a depth of 14 m
Boring done with the help ofbentonite slurry to help stabilize
the walls of the boring till
concreting is done
The grab is tied to the body of the
crane as a safety aspect to prevent
it from hitting any existing building
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Lowering of R/F Cage
R/F Cage for Diaphragm
Wall Panels of Size (5.0
M) made ready before
boring is commenced
Each R/F cage weighs
approximately 10.5 MT
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Concreting for DiaphragmWall
Tremie Concreting done for
Diaphragm Wall
Each Diaphragm Wall Panel is 56
cum
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Excavation up to Bottom of TopSlab
After the Diaphragm Wall is
casted, Excavation for bottom of
top slab is taken up, so that the
inconvenience to the public is
minimum.
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Top Slab
A top slab of 600 mm is casted,
leaving openings at regular
intervals, so that excavation inside
the tunnel can be carried out
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Excavation for Base Slab
After the top slab is casted,
excavation inside the tunnel is
started for base slab works
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Utilities Encountered and Shifting
The identified utilities were diverted temporarily so as to keep the utilities
running & also to make a guide wall for the boring ,these included electrical
cables, communication cables, drainage sewerage etc.
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FACILITIES INSIDE SERVICETUNNEL
HT cables
LT cables
Telecommunication cables
Water supply pipe
Fire water pipes -one for hydrant network system and another forwater sprinkler systems; tapping to be taken from the latter forproviding water spray protection inside the trench.
Irrigation pipeline Gas pipeline.
Air conditioning pipes (chilled water) one for supply & one for
return to the entire Connaught Place areas including P Block,Regal Block & Scindia House Block. Secondary pumping system(one working & one standby) and two heat exchangers required forindividual blocks are to be provided in the tunnel
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