Constructability of underground metro stations depends upon the way we will plan and implement with innovative engineering methods at every stage of construction.As a construction engineer it's really challenge and leanings at high end.

1. Constructability of CMRL
underground Metro stations
of package UAA-04
By
Palla Narasimhudu
ACPM L1 B7

2. Constructability of CMRL under metro stations of package no UAA-o4
 Scope of work: Design and construction of Underground Stations at Nehru Park, KMC
and Pachaiappas College and Associated Tunnels- UAA-04
 Client: Chennai Metro Rail Limited (CMRL)
 Contractor: L&T SUCG JV
 Consultant: EMBYE Consortium
 Type of contract: Engineering Procurement and Construction (EPC)
 Method of Construction: Top Down /Bottom up
Contents of Constructability
1. Geotechnical Investigation and Design of structures / Drawings
2. Utility diversion
3. Traffic Diversion
4. Diaphragm Wall Construction
5. Excavation
6. Roof, Concourse, Base Slab and other structures construction
1. Geotechnical Investigation and Design of Structures/Drawings
Below-ground investigation by boring, sampling, and testing the soil strata to establish its
compressibility, strength, and other characteristics likely to influence a construction project,
and prepare a subsurface profile and soil report. Also called foundation investigation, soil
investigation, soil test, or subsurface investigation. Based on this investigation test reports
Design of structures kick off.

3.  Design conclusions from soil Investigation
 Strut to be provide all Bottom up Excavations
 Nehru Park and Pachiappa’ s station need not required strut while excavation
 KMC station required strut while roof slab as well as base slab excavation.
 During Design process of Diaphragm wall, with or without strut considered additional
reinforcement introduced for without strut structures.
 Length of Diaphragm cage also split into two pieces by advising staggered lap with
welding
 Dewatering bore well location was finalised for ease of excavation
 For Top down construction, temporary openings were finalised
 Wherever sufficient width not available to accommodate traffic, decking proposals
and design
 Connection or Roof, concourse and Base slab with couplers levels and design criteria
 Other station structures like entry, exit, vent shafts, lifts, escalators and Ancillary
buildings all electrical and mechanical works design and drawings.

4. 2. Utility Diversion
Trail pits planned for find out utilities, separate diversion proposal for dry and wet utilities
Based on the area availability we can planned for single stage diversion or inter change, inter
displacement method if area was restricted
In UAA-04 we adopted both methods, all dry utilities diverted in single sage, for wet utilities
both.
The following Utility Diversions shows the constructability of Diaphragm walls (Typical).

6. 3. Traffic diversion
Major concern in underground station construction is traffic diversion, we need to
accommodate existing traffic along with construction activities
Stage vice diversion is only preferable, according to traffic diversion we aligned station
Diaphragm wall works for all three stations .Everywhere we introduced deking to with stand
the traffic
The following traffic diversion shows the achieve constructability of Diaphragm walls
(Typical)

7. 4. Diaphragm wall construction
Diaphragm wall comes under category of deep foundation, it is continuous wall
constructed in ground to facilitate certain construction activities, such as
1. Retaining wall
2. Cut-off provision to support deep excavation
3. Final wall for basement or other underground structure such as tunnel and
shaft
4. Separating structure between major underground facilities
5. Form of foundation such as Barret pile/ Rectangular pile.
Diaphragm wall is a reinforced concrete structure constructed in-situ panel by panel,
this usually is designed at greater depth, mechanical excavation is thus employed by
grabbing/ rig machine
Sequence of activities to achieve constructability of Diaphragm walls (Typical).

8. 5. Excavation
Ground water level is the major concern in excavation, to control /reduce the
ground water level, bore wells and its location, pump water from bore wells and
reduce and always keep the water level one meter below excavation.
Excavation of muck takes place by two methods
Bottom Up : In this method excavation will continue till the base level by providing
the strut with the help of crane and muck bucket . Concrete structure works takes

9. place from base to roof slab. Steel strut to be provide at different levels to with stand
soil pressure.
Bottom up Excavation is a part of constructability of station (Typical)

10. Top down: In this method Excavation will takes place up to Roof slab level ,then
with the help of temporary openings ,excavator will lowered and further excavation
works continued for concourse slab and same as base slab . Where ever required
strut to be provide.

11. 6. Roof, Concourse, Base Slab and other structures construction
Once the excavation completed up to the roof slab level, structural work will complete and
get concreted. Same as per concourse and base also, in base extra water proofing will takes
place before concrete structure erupt. Along with provision for escalator pits, lift pits will also
provide at base.
For Entry and Exits same will follow as described in stations.
All inside construction activities are takes place as a part of constructability of station.

12. Station works under progress