Top Down Method of Construction

8/2/2019 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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Documents

Top Down Method of Construction