A REVIEW OF DELHI METRO TUNNEL CONSTRUCTION WITH 14 EPB SHIELD TBMS
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A REVIEW OF DELHI METRO TUNNEL CONSTRUCTION
WITH 14 EPB SHIELD TBMS
Chitoshi Izumi & Christopher Lovelock1 , Jitendra Tyagi & Subodh Kumar Gupta2
1
Oriental Consultants Co., Ltd., New Delhi, India
2
Delhi Metro Railway Corporation Co., Ltd., New Delhi, India
KEYWORDS: Delhi Metro, Tunnel, TBM
SYNOPSIS
The construction of Delhi Metro Phase-II started in 2006 and was a continuation of the Phase-I
construction. Due to a tight construction schedule, 14 Tunnel Boring Machines have been deployed
to bore 3 metro corridors of twin tunnel with a total drive length of 30km. The purpose of this
paper is to review machine performance under various ground water and soil conditions and also to
introduce the methods employed to overcome the rock formations encountered during excavation
while deployed TBM was for soft soil excavation. Through the various tunnelling performance and
related ground settlement results, several conclusion and recommendation have been deduced for
future tunnelling works within New Delhi area of India.
INTRODUCTION
Delhi Metro Phase-II is mainly an extension of the Phase-I project which was completed in 2006
and consists of the construction of 128km of track, 81 stations and 5 depots. The works comprise
94km of viaduct section and 30 km underground works. This US$ 4 billion scheme has been
jointly funded by the Japanese International Cooperation Agency (JICA), the Government of India
and Delhi Government and is scheduled to be operational in time for the Commonwealth Games of
October 2010. As previously mentioned, because of the tight construction schedule, 14 TBMs have
been employed. The 7.2km of the Qutab Minar Line will make use of six TBMs, four TBMs have
been allocated for a 4.2km stretch of the Badarpur Line and additional four will excavate 3.5km of
the Airport Line.
The first TBM tunnel started on the Qutab Minar Line on 31st December 2007 and at this point in
time 14 TBMs are now in operation. The maximum progress achieved to date by single TBM is 28
rings (33.6m) per day and 426 rings (511m) per month.
GEOLOGICAL CONDITIONS
The geology in the tunnel area for Phase-II construction consists essentially of compacted alluvium
soils known locally as the Delhi silts with isolated outcrops of competent quartzite. The quartzite
forms a range of low hills known as the Ridge, an extension of the Aravalli Mountains which
extend from the south of the territory to the western bank of the Yamuna River. The Delhi silts
which overlie the quartzite bedrock on both sides of the ridge have a differing origin. The Yamuna
flood plain, on the western slopes resembles a fluvial system i.e. containing river deposits whilst the
nearly enclosed Chattarpur alluvial basin contains alluvial soils derived from the adjacent quartzite
ridge.
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4 TBMs
Airport Line
4 TBMs
Badarpur
Line
6 TBMs
Qutab Minar
Line
Figure 1- Route Map and TBM arrangement for Delhi Metro
Phase-I Line-2
New Delhi
Udyog Bhawan
Geological Formation Lajpat Nagar
Airport
Malviya
TBM Section Nagar
: Airport Line
: Qutab Minar Line
: Badarpur Line
Figure 2- Geology of Delhi and TBM Section
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Quartzite
The local quartzite rock has undergone several phases of tectonic activity which has resulted in
fracturing and folding. These disturbances and fluctuations of the bedrock have resulted in intense
and complex weathering patterns in the strata to a depth of concern for construction of tunnel and
stations. An assessment of the in-situ rock mass was made using Rock Mass Rating (RMR)
methodology published by Bieniawski. The majority of rock encountered by the Airport Line
belongs in the “Poor Class” with an RMR value within the range of 21 to 40. The results of
unconfined Uniaixial Compressive Strength (UCS) tests are inconsistent and vary within a range
from 20 to 160 MPa.
Alluvium
The Delhi silt encountered along the entire route
and the thickness of the alluvium deposits
depends upon the sub surface bedrock
topography infilling the previous topography.
The alluvium is generally a fine grained
material consisting of gradational variations
between clay and silt with variable fine sand
content. The soils are occasionally difficult to
accurately describe by visual assessment alone
due to their borderline clay/silt nature. A
conspicuous feature of the alluvium is the
presence of generally coarse sand to medium，
occasionally coarse，gravel sized buff coloured
calcareous nodules. These are found scattered
throughout the stratum and are locally termed
“Kankar”. Although some cohesion has been
observed, a value of 0 kN/m2 was assumed for
static calculation and the friction angle was
Figure 3- Typical SPT for Delhi silt
assumed to vary within a range of 30 to 32
degrees.
Ground water
The ground water level varies from GL-10m (typical tunnel crown level) to GL-35m. Tunnel
excavation can be carried out in open mode for the southern portion of the Qutab Minar Line and
sections of the Airport Line because the ground water level is below the tunnel invert. This has
contributed to the relatively good rates of progress for these TBMs.
TBM CHARACTERISTICS
As previously mentioned, the majority of the stratum encountered in the tunnel excavation consists
of the Delhi silt which is relatively dense sandy silt or silty sand with localized outcrops of quartzite
in various stages of decomposition. As a result all the Contractors on Phase-II selected Earth
Pressure Balance Machines (EPBM) with diameters of 6.5 to 6.6m.
The TBM suppliers and conditions are as follows:
• Contract BC16 (Qutab Minar Line): 2 TBMs by Herrenknecht (HK) and 2 TBMs by Robbins
with Mitsubishi
• Contract BC18 (Qutab Minar Line) : 2 TBMs by HK (Refurbished after Phase-I construction)
• Contract BC24 (Badarpur Line) : 4 TBMs by HK
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• Contract AMEL-C1 (Airport Line) : 2 TBMs by HK (Refurbished from C855 in Singapore)
• Contract AMEL-C5 (Airport Line) : 2 TBMs by Okumura Machinery Corporation
For the above machines, the TBM specifications are summarized below;
Table 1- EPB TBMs Specification
Contract BC16 BC18 BC24 AMEL- AMEL-
C1 C5
TBM Supplier Herrenk- Robbins HK HK HK Okumura
necht with
(HK) Mitsubishi
TBM Numbers Ps 2 2 2 4 2 2
Drive length/ TBM m 1,990 2,030 3,150 1,920, 2,200 1,300
2,240
Geology Delhi silt, Delhi silt Delhi silt Delhi silt Delhi silt, Delhi silt
quartzite quartzite
Ground water (GL- ) m 15-30m 10-15m No water 5-10m 14m No water
Shield Diameter m 6.54 6.52 6.49 6.64 6.64 6.41
Shield Length m 7.7 8.8 6.0 7.6 7.6 8.3
Articulation jack - No No Yes Yes Yes No
Main drive power Kw 630 810 945 630 1600 1800
Thrust force Kn 35186 32000 34835 33260 42575 48000
Cutter face torque Knm 4346 5148 4085 4346 4474 5652
The minimum horizontal curvature of BC16 tunnel was R=600m which was relatively gentle
compared to that of other contracts on Phase-II. The Contractor ordered TBMs without articulation
jacks because theoretically there is sufficient clearance to manage such a curvature with a proper
arrangement of tapered segments. However, damages to segments, in the form of cracks and
spalling occurred at initial stage of driving. These damages are observed around circumferential
bolts hole at horizontal curve sides and it considered they result from eccentric and concentrate
loading onto the segments, a relatively small annular void between the extrados of the segments and
the tail skin and operator error. This damage might have been mitigated by use of articulation jacks.
Apart from BC16 and AMEL-C5 all of the TBMs have been fitted with roller disks at perimeter of
cutter head to assist with cutting the profile at the launch & arrival shafts through the diaphragm
wall panels. Because the ground condition were relatively good with a reasonable stand up time,
most of the soft eyes were broken in advance of the TBM launch or arrival with the arrangement of
temporary wall by lean mix mortar or steel piles behind the diaphragm wall together with localized
dewatering.
Since the Delhi silt comprises of alluvial soils derived from the adjacent quartzite it contains
significant quantities of sand which resulted in wear problems for the cutter heads during TBM
operation. To overcome this problem additional hard face welding was provided to the cutter heads
between drives. Some of Roller disks became choked with clay particles which prevented their free
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rotation and resulted in uneven wear. Typically 30-80% of cutter bits were replaced after 0.6–1.4
Km of individual drive completion.
Full Face Cutter head (BC16, BC18, BC24, Spoke Type Cutter head (BC16 and AMEL-C5)
and AMEL-C1)
Figure 4- Typical Cutter heads of TBMs for Delhi Metro Phase-II
TUNNELLING PERFORMANCE AND CASE STUDY
Tunnel Progress
Tunnel progress is related to numerous factors such as ground conditions (including the presence of
ground water), dictated TBM operation parameters such as to surface structures, size of launching
shaft and back up arrangements, capacity of gantry cranes and muck pit size, etc. Table 2 indicates
the tunnel progress recorded for each tunnel operation.
The launching shafts for BC18 and BC24 North tunnel operation were 60m in length and proved
advantageous allowing back up gantries installation at one time for the initial drives. The shaft
lengths of other contracts were dictated by external parameters and varied from 17m – 20m. The
contractors accepted a slower progress for the initial drives and installed a number of switches with
the tunnel to speed up mucking operations where possible.
Table 2- EPB TBMs Progress up to End of February, 2009
Contract BC16 BC18 BC24 AMEL- AMEL-
C1 C5
TBM Supplier HK Robbins HK HK HK Okumura
Daily progress: Average (m) 8 9 12 6 9 5
Daily progress: Maximum (m) 29 34 28 27 24 15
Weekly progress: Maximum(m) 167 180 150 141 111 47
Monthly progress: Maximum(m) 392 440 511 404 402 140
Note: 1) Average progress derives from tunnel drive length divided by duration from TBM launch to arrival.
2) The condition of AMEL-C5 is just after initial drive stage.
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Surface Settlement and Volume Loss
Generally surface settlements were managed well through all the drives. The main reasons for this
was proper TBM operational procedures including applied face pressure, the relatively long stand
up time of the Delhi silts and sufficient ground cover more than 1.5D (D: Tunnel diameter). The
surface settlement values by excavation of 2 single tunnels were recorded in the range of 5mm to 20
mm and volume loss was typically 0.3 – 0.8%. During tunnel excavation, several minor cracks
were observed in non-structural members, namely surface of brick walls of some 2-3 storey
residential properties. Repairs to these walls were typically undertaken after completion of the
tunnel drives.
(mm)
0
5
10 1st TBM
Passing
15
20
2nd TBM
25 Passing
Date
Figure 5- Surface Settlement by Tunnel Excavation & Cracks observed on wall surface
Rock Encountering by BC16 Tunnelling
During tunnel excavation at the INA-JB section of the Qutab Minar Line, the UP Line TBM
encountered rock while TBM face was for soft soil mining. Initial geotechnical investigations (G.I.)
were not sufficient to cover the rock profile for this section. Additional G.I. were undertaken and
confirmed the presence of hard quartzite rock with a UCS in the range of 100 - 160 Mpa dipping
steeply down from west to east for 100m of the tunnel alignment. Because of the steep inclination
of the rock formation, the DN Line tunnel was unaffected as shown in Figure 6. The contractor
proposed the following options to overcome this problem, but both of them were rejected because
of the site difficulties;
- Change the construction method to Cut & Cover tunnel: there are 20-30 number of old trees to
be cut and it is difficult to get permission from authority.
- Change the construction method to NATM: the rock is located at only bottom half and top half
is consist of soft soil. Stability measures such as pipe roofing, soil improvement and dewatering
would be required and this it not readily available in Delhi.
According to the suggestion from TBM supplier, the Contractor proposed to change the cutter face
from soft soil mining face to hard rock mining face which was available from Singapore project
C855. It was very fortunate because TBM size and main specification were similar between the two
projects and replacement works could be done relatively smoothly. After fixing the TBM with hard
rock face, an average 3.9 rings (4.7m) progress per day was attained and mining works were
completed within 20 days for 100m stretch.
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6540 mm
CH. 24+000 CH. 23+975 CH. 23+950 CH. 23+915
Figure 6- Typical section (UP Line) of TBM and rock formation at each chainage
Figure 7- Temporary shaft and Setting of Cutter face from C855
CONCLUSION
With a scheduled target date for testing & commissioning of rolling stock in the first quarter of
2010, all civil works should be finished by no later than the third quarter of 2009. So far out of 14
TBMs, 3 TBMs in Qutab Minar Line have completed their operations whilst 11 TBMs are still
excavating in full swing. It is still too early to evaluate tunnelling operation for the entire Delhi
Metro Phase-II, but through this study of tunnelling performance and with the experience gained,
the following observations and recommendations can be made for the future tunnelling works
within the region:
1) According to the geology of Delhi, quartzite rock is often encountered underground and causes
problems for underground construction works. Prospective contractors should undertake
proving tests to locate the level of the rock head prior to construction at 20m to 30m centres
along the tunnel alignment using portable Dynamic Penetration Rig or Ground Penetrating
Radar System (GPRS) where possible.
2) TBMs equipped with rock cutting discs mounted along the periphery of the cutter head as a
minimum should be employed not only for breaking through tunnel eye at TBM launch and
arrival but also for mining the rock under unforeseen condition.
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3) The ground surface settlement could be managed well under open mode of TBM operation in
the dense Delhi silt. Open mode operation is acceptable provided that the water table is well
below than excavation level and surface structures and utilities are located away from influence
zone.
4) Under well managed condition in main drive, daily tunnel progress of 20m (15 to 16 rings per
day) is readily achievable in the Delhi silt formations.
5) Ground surface settlement by controlled tunnel operation is relatively small, namely 5mm to
20mm by 2 single tunnel excavations in the dense Delhi silt and volume loss can be controlled
to a range of 0.3 to 0.8%.
Delhi Metro is the first Client in India to apply EPB technology in an urban area. A comparison of
the merits of the various tunnelling machines and their tunnelling performance is of interest to many
because of future metro projects planned for Mumbai, Chennai, Kolkata and Bangalore.
ACKNOWLEDGEMENTS
We would like to thank civil contractors, namely Continental Engineering Corporation-Soma JV
(BC16), Dywidag-L&T-Samsung-Ircon-Shimizu JV (BC18), Italian-Thai Development JV (BC24),
Alpine-Samsung-HCC JV (AMEL-C1) and L&T-SUCG JV (AMEL-C5) for giving the data of
tunneling works. We also thank Mr. Ravindra Dutta (Tunnel Expert from RITES) and Dr. Ateeq
Khateeb (Geotechnical Manager for BC18 Contractor) for their assistance.
REFERENCES
H. R. Yadav (2005), “Geotechnical Evaluation and Analysis of Delhi Metro Tunnels”, Indian Institute of Technology,
Delhi, PP. 59-65.
Mott MacDonald (2001), “Delhi Metro Contract MC1B Interim Geotechnical Interpretative Report”, International
Metro Civil Contractors, Delhi
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