REPORT ON DMRC INDUSTRIAL TRAINING

1. DELHI METRO RAIL CORPORATION
The Delhi Metro is a mass-rapid transit system serving Delhi, Gurgaon, Noida and Ghaziabad in the
National Capital Region of India. Delhi Metro is a metro system serving Delhi, Gurgaon, Noida,
and Ghaziabad in the National Capital Region of India. Delhi Metro is the world's thirteenth largest
metro system in terms of length. Delhi Metro is India's second urban mass rapid transportation
system, after Kolkata Metro. As of June 2014, the network consists of five colour-coded lines (Red,
Blue, Green, Yellow, Violet), plus a sixth .Airport Express line, with a total length of 193.2
kilometres serving 139 stations, (including the 6 Airport Express stations), of which 38 are
underground, five are at-grade, and the rest are elevated.
It is also India’s first modern public transportation system, which has revolutionized travel by
providing a fast, reliable, safe and comfortable means of transport. The present network consists of
six lines with a total length of 189.63km with 142 stations. Delhi Metro was planned to be built in
phases spread over around 20 years as with each phase having a target of five years and end of one
phase marking the beginning of another. Phase I (65 km) and Phase II (125 km) were completed in
2006 and 2011, respectively, and Phase III and Phase IV are scheduled for completion in 2016 and
2021, respectively. Work on Phase III started in 2011 while planning for Phase IV has begun. Ex-
chief of DMRC hinted that by the time Phase IV is completed, the city will need Phase V to cope
with rising population and transport needs.
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2. LARSEN & TOUBRO
Larsen & Toubro Limited (L&T) is amongst one of India’s largest technology, engineering
construction and manufacturing conglomerate. L&T is considered to be the "bellwether of India's
engineering sector”, and was recognized as the company of the year in 2010. Its business structure
has a dominant presence in India's infrastructure, power, hydrocarbon, machinery, shipbuilding and
railway sectors. L&T has an international presence. The company's businesses are supported by a
wide marketing and distribution network, and have established a reputation for strong customer
support. With more than a seven decades of dedicated customer focused service and continuous
quest for world class quality have established them as the leader of the Engineering and Construction
sector in India.
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3. SHANGHAI URBAN CONSTRUCTION GROUP
SUCG Infrastructure India Pvt. Ltd. is an international company which integrates overseas
construction, design and management, investment, and sales of construction equipment. Shanghai
Urban Construction (Group) Corporation, established in October 1996 with the approval of Shanghai
Municipal Party Committee and the Government, is a comprehensive enterprise particularly
supported by the Ministry of Construction and Shanghai Municipal Government. It is authorized by
Shanghai State-owned Asset Management Committee to manage the state-owned assets within the
Group. Shanghai Urban Construction (Group) Corporation has the special class qualification for
municipal public works, the first-class general contracting qualifications for highway construction,
housing, etc.
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4. L&T SUCG JV CC-27, New Delhi PROJECT FEATURES
INTRODUCTION
L&T in a joint venture with SUCG won an order worth 12.526 billion from DMRC.
CONTRACT FEATURES
Under the terms of the contract, the Heavy Infrastructure IC of L&T Construction and SUCG will
design and construct a tunnel between Shankar Vihar and Hauz Khas, as well as underground
stations at Vasant Vihar, Munirka, R.K. Puram, I.I.T. and Hauz Khas.
CONTRACT
Design and construction of tunnel from end of underground ramp (Near Shankar Vihar Metro
Station) to Hauz Khas Metro Station and an underground ramp near Shankar Vihar Metro Station
and underground Metro Stations at Vasant Vihar, Munirka, R.K. Puram, I.I.T. and Hauz Khas on
Janakpuri West-Botanical Garden corridor of Delhi Metro Project of Phase-III .
PROJECT FEATURES
CLIENT : DELHI METRO RAIL CORPORATION LTD.
CONTRACTOR : L&T-SUCG JOINT VENTURE
BUDGET OF CONTRACT : INR 1252.6 Cr
CONTRACT PERIOD : 42 Months
START DATE : November 1st 2012
COMPLETION DATE : May 9th 2016
LENGTH OF PROJECT : 6.82 KM
CASTING YARD : Mundka
BATCHING PLANT : Pushp Vihar
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5. GEOTECHNICALREPORT
Before starting construction, Geotechnical data was collected from various locations along the
proposed route to know about the soil characteristics. Bore Holes were made along the proposed
route up to a depth of 30M below existing ground level or REFUSAL whichever is first.
Refusal here is defined as when SPT field value reaches 100 or more for a penetration of 30cm
or less. And where ever refusal is encountered before reaching the required depth. The bore hole
is extended further by using HYDRAULIC FEED ROTARY DRILLING.
SPT (Standard Penetration Test was carried out every 1.5m interval and disturbed soil samples were
collected. Undisturbed soil samples were collected at every 3m or change of strata which ever was
earlier. So in total 45 bore holes were dug out. Split spoon sampler was used for collecting the
samples.
Boring was done using Shell and auger method and IS 1892-1979 was followed.
Following tests were then performed on the collected samples-
 Sieve analysis. 

 Hydrometer testing 

 Moisture content 

 Specific gravity 

 Dry Density 

 Atterbergs limit 

 Triaxial shear test(uu, cu, cd) 

 Consolidation test 

 Direct Shear Test 

 Chemical analysis of both soil and water samples 
The collected rock core samples were taken and the following tests were conducted on them-
 Density test 
 Water absorption& porosity 
 Hardness 
 Ucs 
 Point load index 
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6.  STUDY OF BORE HOLE DATA
 Standard penetration tests were conducted in the above bore holes at regular interval in depth &
at change of strata as per specifications / instructions of Engineer-in-Charge. The bores were
cleaned up to the desired depths. Standard split spoon sampler attached to lower end of a drill
rods was driven in the bore holes by means of standard hammer of 65.0 kg falling freely from a
height of 75 cm. The sampler was driven 45 cm as per specifications & the number of blows
required for each 15 cm penetration were recorded. The number of blows for the first 15 cm
were not taken into account. This was considered as seating drive. Wherever total penetration
was less than 45 cm, the number of blows & the depth penetrated is incorporated in the
respective bore logs. The number of blows for next 30 cm penetration were designated as SPT
'N' value. Disturbed soil samples obtained from standard split spoon sampler for all the above
standard penetration tests were collected in polythene bags of suitable size. These samples were
properly sealed labeled, recorded and carefully transported to the laboratory for testing. 

 Undisturbed soil samples were collected from the bore holes at regular interval in depth & at
change of strata as per sampling specifications, in thin walled sampling tubes of 100 mm dia
and 450 mm length fitted to an adopter with ball and socket arrangement were collected. 

These sampling tubes after retrieval from the bore holes were properly sealed at both ends.
These were carefully labeled and transported to the laboratory for testing. 

 The depth of ground water table was checked/measured in all the bore holes, after completion of
bore holes & on full stabilization of ground water table.Bore holes through all type of soils were
bored using shell and auger method. Further bore holes through rocky strata were drilled using
hydraulic feed rotary drilling machine with double tube core barrel. To retain the bore holes the
casing pipe was used up to the entire. 

 Ground water samples were collected from bore holes BH-35 & BH-36 and stored in suitable
plastic containers of 5 litre capacity having air tight lids. The samples were properly labeled,
scaled and carefully transported to the laboratory for chemical analysis. 

Geotechnical report Data suggested using


1. Bottom-up Construction technique for construction at VASANT VIHAR SITE
2. Top To Bottom Construction for HAUZ KHAS SITE.
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7. TOP TO BOTTOM & BOTTOM UP CONSTRUCTION
As suggested by Geotechnical data, suitable methods are selected for construction at sites according
to the location and soil properties. Here we are going to discuss about 2 such methods
 Bottom Up construction 

 Top to Bottom construction 
The choice of selection of method depends on a so many factors like-
 Soil Profile- As suggested by the geotechnical investigation. 

 Site Location-The site is located in an isolated environment or urban dwellings. 

 Cost Incurred -Depends 

 Surrounding Environment-Weather the Surrounding environment consists of existing
structures and road networks. 

 Time Constrain-The total time available for completion of project. 

 Availability of Material-The availability of material for filling and construction Activities to
be carried out. 
Both the methods have their own merits and demerits and we will study about the methods one at
a time.

BOTTOM-UP CONSTRUCTION




 Vasant Vihar is the only metro station of the project CC-27 which is constructed
using Bottom-Up construction methodology. The ground profile of this station is
Medium hard rocks. As a result of this, bottom-up method is preferred for this
particular station. 

TOP VIEW-VASANT VIHAR 
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8. Bottom-Up Method
Length: 265 m
TBM Tunnel: 1443m
C&C Tunnel: 103 m
 In bottom-up construction, a trench is excavated more than the required size of the
station. Then the trench is backfilled and the surface is restored afterwards. 

 Important components in bottom
up approach are 
- Earthwork
-Excavation
-Temporary Retaining structures
-Rock anchoring
-Strut waler arrangement.
EXCAVATION BEING CARRIED OUT
-RCC Works-Columns, Slabs
EXCAVATION
 Excavation should be carried out by mechanized method up to the formation level at stages.
The activities for carrying out excavation are mainly rock excavation, shot crete, rock
bolting, disposal of excavated materials and grout monitoring. 

 Excavation should be carried out in proper sequence. 

 Also, the site should be checked for utility lines and proper diversions should be done
beforehand. Traffic divers on plans should be made and it should be diverted before
starting the excavation. 

 According to IS 3764:1992(Code of safety for excavation work). 

 All trenches in soil more than 1.5 m deep shall be securely shored and timbered. 

 All trenches in unstable rock exceeding 2 m in depth shall be securely shored and timbered. 

 Excavation of the soil can be done in many ways depending on the soil profile. 
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9. Braced excavation method-
Installing horizontal struts (use lateral pressure
against lateral soil pressure) in front of retaining
walls to resist the earth pressure on the backs of
walls is called the braced excavation method. The
bracing system consists of horizontal and diagonal
struts, Waler beams, king posts and runner beams.
In Project CC- 27, the structural steel used for
fabrication of all these components of the bracing system using UB 610(Universal Beam). The
function of Waler beams is to transfer the
earth pressure on the back of the walls to the
strut assembly. Installation of the bracing struts
is done by excavating soil locally around the
strut and only continuing the excavation once
preloading is complete. Cross-lot bracing makes
sense in narrow excavations (60ft to
120ft) when tieback installation is not feasible. The struts can bend excessively under their own
weight if the excavation spacing is too large. In addition, special provisions have to taken to account
for thermal expansion and contraction of the struts.
SOLDIER PILES-Soldier piles or soldier beams are H-
piling set in predrilled holes around the periphery of an
excavation. Pre drilling as opposed to driving is used to
provide close control of alignment and location. These
piles are then grouted in place with weak concrete.
Lagging is the timber placed horizontally between the
soldier piles to retain the soil behind the excavated area. Pairs of soldier beams are driven to a depth
slightly below the final excavation. Their spacing is in the order of 2-4 meter so that available timber
can be used for lagging. The lagging timber, which is slightly shorter than the spacing but on the
order of 2 to 4 inches thick, are installed behind the front flange to retain the soil as excavation
proceeds. Some hand excavation is usually required to get the lagging into the place.
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10. Soldier piles are installed with conventional pile-driving equipment or in augured holes. The
horizontal sheeting or lagging is installed behind the flange closest to the excavation (inside flange).
The sheeting can be installed on the inside face of the front flange and held in place by various
methods such as clips, welded studs, or bars, etc. The soldier pile and lagging method is
inappropriate for perfectly cohesion less soil. For cohesion less soils sheeting must be used.
2-4 Meters
ADVANTAGES DISADVANTAGES
I Easier and faster construction with lower I Sealing is difficult. In sandy soils with high
cost. groundwater level some dewatering measures
2 Piles can be easily pulled out. may be necessary.
3 It is necessary that less ground disturbance 2 Installing soldier piles by striking will cause
is caused when pulling out the piles, much noise and vibration. The latter will render
compared to pulling out sheet piles. sandy soils below the foundation denser in such
4 The pile tip can be strengthened with special a way that uneven settlement of the adjacent
steel materials for use in gravel soils. buildings may occur.
5 Soldier piles are reusable. 3 Backfilling is necessary if soldier piles are
driven using pre-boring.
5 Removing piles will disturb the surrounding
soil.
Anchored Excavation Methods-
Anchored excavation methods substitute anchors force to counteract the lateral earth pressure. The
configuration of an anchor can be divided into
(a) The fixed section- which offers anchoring force
(b) The free section- which transfers the anchoring force to the anchor head.
(c) The anchor head- which locks the tendons and transfers the anchoring force to the structure.
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11. The anchored excavation counts solely on soil strength to offer the anchoring strength. The
higher the soil strength, the stronger the anchoring force and vice-versa. Granular soils as sandy
soils
or gravel soils have high strengths and thus offer strong
anchoring force while clay has weak strength and creep will further decrease the anchoring force.
Therefore, the anchoring section should avoid being installed in clay.
The anchorage process involves the following steps
o Drilling Processes
o Anchor installation and grouting
o Waler beam installation
o Pre Stressing
o De-Stressing
o Quality Assurance and quality control(Qa-Qc Procedures)
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12. SHORTCRETE
Shortcrete is concrete conveyed through a hose and pneumatically projected at high velocity onto
the excavated surface, as a technique for stabilizing the excavated face. Shortcrete is usually an
all-inclusive term that can be used for both wet-mix and dry-mix versions. Shortcrete undergoes
placement and compaction at the same time due to the force with which it is projected from the
nozzle. Cement, sand, aggregates and water are the main constituents of shotcrete. Prior to the
application of shotcrete, all surfaces to receive shotcrete shall be cleaned with compressed air.
o Admixtures: Admixtures for the improvement of performance, workability, etc.
o Water: Water free from solid suspended matter and organic particles confirming to IS: 456-
2000
o Flyash: Flash shall comply with Specification IS:3812.
o Accelerator: Accelerator will be Alkali free, and dose will be max. 6% by wt. of Cement.
-After the preparation of surfaces 4mm wire
mesh is fixed to the concrete surface with pin of
8m dia and to the earth surface with 25-32mm
dia reinforcement bar 1500-3000mm c/c.
-The operation temperature for Shortcrete is 5
– 32deg Celsius.
-MIX DESIGN PROPORTION IS USUALLY
BETWEEN 1:3 to 1:5 depending upon
the surface.
-Shortcrete is transported by transit mixer from
the batching plant to site and will be delivered
into hopper of concrete spraying machine.
-The designed thickness of the Shortcrete will be built up in layers of about 75mm thick. The
nozzle for spraying will be kept at a distance of 1 to 1.4m away from surface and always
perpendicular to the surface.
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13. -Before a subsequent layer of shortcrete is applied the percentage layer will be checked for
defects like voids, dry or sandy patches will be cut and then re-Shortcrete.
-The area of spray should not be less than 300mm*300mm.
-Initially fix the wire mesh then spray the Shortcrete up to 75mm, after the drill hole for
installation of rock bolt. So Shortcrete around rock bolt is not required.
-To check the thickness of the Shortcrete coring will be done.
ON FIELD
1) Clean the surface off the loose material and then clean with air compressor.
2) Apply a layer of shortcrete to the surface and wait for it to cure.
3) Apply the wire mesh on the surface and bind it to the surface using reinforcements.
4) Now apply the second layer of the shortcrete on the surface.
After excavation we will further study about the bottom-up construction in the sequence
of slabs.
1. SLABS
BASE SLAB-
The major work of the base slab is to support the tracks and resist the vertical pressure from the
ground. The construction process to construct this slab is also the same as the roof slab and the
concourse slab. The base slab is placed 6.86 meters below the base of concourse slab and it is
900mm thick. The base slab structure is not flat but in shape of a bucket with leaves at the ends.
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14. For the construction of the base slab this soil is then lined with 75mm (min) thick PCC layer
and 3mm thick ply. These ply act as a base support for the concrete layer, it also gives a fine
finish. As shown in the above figure
BUCKET-LEAF STRUCTURE OFBASE SLAB
MATERIALS USED
-Concrete conforming to M40 grade shall be used for
casting. -Reinforcement conforming to FE500D shall be
used on site. -Water shall conform to IS456.
-Water Stops –PVC water stop will be used to arrest the water leakage as specified in the
drawing. -Binding wire used for binding reinforcement has a core dia of 1.25mm
-Formwork panel would be made of film coated plywood.12mm thick and shall be placed along
the alignment and the verticality and level shall be checked.
-Cover blocks should be used depending on clearance that needs to be provided to
the reinforcement.
-Minimum lift period for the formwork are as
follows--Vibrator of 60mm dia 4nos
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15. CONCRETING
-Before concreting the area are shall be cleaned using a boom pressure with air or water.
-M40 grade of concrete shall be used along with waterproofing admixture of crystalline typewhich
would be mixed with the concrete at the batching
plant during mixing.
-Concreting temperature shall be between 32 deg
Celsius to 5deg Celsius and concrete shall be
placed using boom placer/bucket whoever serves
the purpose.
-In order to avoid cold joints the concrete shall be
placed in continuous layers not exceeding 300mm
and it should be kept in mind to compact each layer efficiently and completely by immersion
of vibrators before second layer is laid down
-Reason for cold joints-Cold joints are formed primarily between two batches of concrete where the
delivery and placement of the second batch has been delayed and the initial placed and compacted
concrete has started to set. The full knitting together of the two batches of concrete under vibration
to form a homogeneous mass is therefore not possible, unlike the compaction of two fresh workable
batches of concrete. This could be a potential plane of weakness.
Remedy for cold joints-Proper compaction of the layer beneath and subsequent poring of
second layer without any delay so that the layer below is still green (FRESH).
Needle VibratorsBeingusedatSite
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16. COMPACTION
The concrete shall be compacted before the initial setting of the concrete has started. Immersion
vibrators shall be used for the compaction of concrete and the immersion vibrators shall be used in
a near vertical position and shall penetrate the full depth of the layer of concrete and just in to the
layer below as shown in the above figure. Vibration shall be done continuously until the expulsion
of air has practically ceased and in manner which does not promote segregation of the ingredients.
The vibrator shall not be allow to come into contact with the reinforcement and formwork. Screed
vibrators may be used for vibration of the surface Screed vibrators are very useful for smooth finish
and compaction of green concrete preventing the formation of thermal crack on the top layer.
The pour sequence for concrete adopted is shown below in the figure and should be followed strictly.
CURING
After the final set has taken place wet hessian cloth shall be placed and covered by polythene sheet.
The hessian cloth shall be kept permanently damp
-After 24Hours hessian cloth and the polythene sheet shall be removed and the area would be
ponded with water .For vertical curing the
hessian cloth along with polythene
sheet shall secure the surface for at
least 7 days before next vertical
pouring begins. The hessian cloth
should be damp all the time.
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17. CONCOURSE SLAB/ INTERMEDIATE SLAB
CONCOURSE SLAB
Outlook of the station is said to be concourse slab. The activities at the station other than the train
Tracks are all available on this slab. The slab serves as the gallery of the metro station. It contains
the entry and exit gates to the station, the ticket counters, and security and fire escape provisions.
The construction of the concourse slab is carried out in the same manner as the roof slab. This slab
contains larger temporary cut-outs than the roof slab. These cut-out spaces help in the laying and
development of the base slab and lowering of TBM for tunneling. These cut-outs are closed during the
final phase of the construction. These cutouts are initially supported by beams to provide stability to
the D-walls. These beams are removed after the structure is stabilized by the construction of the base
slab. The concourse slab is placed 5.25m below the base of the roof slab. Its thickness is 550mm. The
concourse slab contains exhaust vents (Over Track Exhaust ducts) at the sides of the slab. The
concourse slab contains the cavity provided to place the service lines inside the station. The concourse
slab is connected to the base slab with the help of stair case, escalator and lift.
MATERIALS USED
-Concrete conforming to M40 grade shall be used for casting.
-Reinforcement conforming to FE500D shall be used on site.
-Water shall conform to IS456.
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18. -Water Stops –PVC water stop will be used to arrest the water leakage as specified in the drawing.
-Binding wire used for binding reinforcement has a core dia of 1.25mm
-Formwork panel would be made of film coated plywood.12mm thick and shall be placed along
the alignment and the verticality, fine and level shall be checked.
-Cover blocks should be used depending on clearance that needs to be provided to
the reinforcement.
ROOF SLAB
The base slab supports the whole weight of the station. The diaphragm walls of the station sustain
huge amounts of lateral pressure from the backfill. This makes the diaphragm wall act as a
cantilever and it tends to lean inwards, but to sustain the pressure the roof slab is constructed. The
roof slab provides the support at one point. The concourse slab built after the roof slab provides
extra support to the D-wall. When the roof slab is constructed, it completes the box structure and
provides additional support and gives stability to the structure, the roof slab is designed to take the
weight of filling and any subsequent structure that may be built on it. At the time of making of roof
slab, several cut-outs are left for further excavation required for construction of concourse and base
slab and for lowering of TBM for tunneling. The thickness of roof slab is 1.8- 2 meters.
ROOF SLAB SATELLITE VIEW WITH CUT OUTS IN THE ROOF SLAB
19

19. Material required- Same as above
And all other considerations are same as those of base slab and concourse slab. Except that
water proofing has to provide over roof slab, which has been discussed later in the project.
3) WALL
Concrete Pouring of Wall:
(1) All concrete shall be produced
at batching plant using approved
mix design. The Process of
batching, mixing and delivery of
concrete to site shall be carried
out as per the specification.
(2) Concrete shall be transported to
site by transit mixer from batching
plant.
(3) Concrete shall be placed by using concrete pump/Boom placer/Hopper of required capacity.
Elephanta pipes will be added bottom of Hopper /13oom placer if required.
(4) After ensuring the completion of reinforcement and fixing & shuttering support as per
formwork drawing of wall, concreting work is commenced.
(5) Pouring will be done 1 meter depth per hour only. Concrete will be compacted properly.
Immersion type vibrators will be used for compaction of concrete. Vibrators will be operated in
near vertical position. Vibration will be applied continuously until the expansion of air has
practically ceased and in a manner which does not promote segregation of the ingredients and is
withdrawn slowly to avoid there formation of voids.
(6) Tampering will be done with wooden hammer to take out entrap air out from concrete
where required.
(7) Curing will commence as the concrete attains sufficient strength.
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20. 4) FILLING OPERATION
PREQUISTITES
1 All repair work for concrete surfaces (if any) should have been done and inspected before
start backfilling it should be ensured that the wall surface is in good condition
2. Bed level of the backfilled area will be checked and remove all foreign materials not needed
(i.e. debris. stones. planks. oil if any).
3 Necessary equipment tools (Vibro-tamper, survey tools, lab tools) will be arranged to be ready
for the work.
4 A sample from the proposed backfill
material to be tested in the site lab to
identify its conformance with the project
specifications
5 Backfilling around structures will not
commence until the structural elements
have attained adequate strength.
Backfilling will be carried out in the
following steps:
Backfilling with Sand / Pond of Cavity
behind Retaining Wall
1. Backfill sand conforming to the
Contractual requirements will be used to
backfill behind the cavity between the
RCC Wall and supported rock surface.
2 Sand will be spread on the area to be backfilled uniformly using a loader/dozer.
3 The backfilling around structures shall be done in layers of compacted thickness between
500mm to 1m.
21

21. 4 After each layer is laid, water will be sprayed through hose pipe arrangement on the surface
for water consolidation. Hence, before the next layer begins chances of settlement of the
consolidated surface will be taken care of.
5 Rollers shall be used for compaction.
6 The compaction shall be done in a longitudinal direction along the area along the area and shall
generally being at the outer edges and progress towards the center in such a manner that each section
receives equal compaction effort
7 Before laying the next layer Water shall be sprinkled for proper bonding of the layers.
22

22. TUNNELING
Tunnels are feasible alternatives to cross a water body or traverse through physical barriers such as
mountains, existing roadways, railroads, or facilities; or to satisfy environmental or ecological
requirements. The tunneling in CC-27 project is taken care by SUCG Infrastructure Pvt. Ltd. There are
different techniques of tunneling viz. drilling and blasting, NATM, hydraulic splitter, slurry shield
machine, etc. All the tunnels in project CC-27 are to be made using TBM. A Tunnel Boring Machine
(TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section
through a variety of soil and rock strata. TBMs and associated back-up systems are used to highly
automate the entire tunneling process, reducing tunnelling costs. In certain predominantly urban
applications, tunnel boring is viewed as quick and cost effective alternative to laying surface rails and
roads. Expensive compulsory purchase of buildings and land, with potentially lengthy planning
inquiries, is eliminated.
USE OF TUNNELS BY DMRC
Tunnels & Underground stations were provided due to environmental & space constrains further tunnels
allow for estate developments over them. Underground structures have an added advantage of a longer
structure life as compared to those on ground.
TYPES OF TBM
SINGLE SHIELD TBM:
A single shield machine uses pre-fitted segments to exert the blast force on the working face. Digging
time represents approximately 80% of operating time, the remaining 20% corresponding to segment
fitting.
1) Cutter head
2) Shield 3) Belt conveyor 4)
Excavated material removal
trolley
23

23. DOUBLE SHIELD TBM (USED AT VASANT VIHAR)
Machines allow for faster tunnel excavation as the segments are fitted in concurrent operation time
during blasting (digging). In this case, digging time approaches 100% of operating time. The rear
shield is fitted with grippers.
The TBMs operating in Project CC-27 are:
THI 1 TBM
THI 2 TBM
Okumura TBM
Herrenknecht TBM
Mitsubishi TBM
Selection of TBM depends on many factors of
which the most important factor is the ground
profile. These TBMs can also be broadly
classified into Soil TBM, Mixed TBM and Rock
TBM. A TBM typically consists of one or two
shields (large metal cylinders) and trailing
support mechanisms. At the front end of the
shield is a rotating cutting wheel. Behind the
cutting wheel is a chamber where, depending on
the type of the TBM, the excavated soil is mixed
with slurry. Systems for removal of the soil are also incorporated into the machine system.
Behind the chamber there is a set of hydraulic
jacks supported by the finished part of the tunnel
which push the TBM forward.
24