Constructability of CMRL

underground Metro stations

of package UAA-04

By

Palla Narasimhudu

ACPM L1 B7

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.

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.

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).

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)

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).

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

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)

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.

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.

Station works under progress