Paper on Phase 2 Izumi, Tyagi, Lovelock

8/3/2019 Paper on Phase 2 Izumi, Tyagi, Lovelock

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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

1Oriental Consultants Co., Ltd., New Delhi, India

2Delhi Metro Railway Corporation Co., Ltd., New Delhi, India

KEYWORDS: Delhi Metro, Tunnel, TBM

SYNOPSISThe construction of Delhi Metro Phase-II started in 2006 and was a continuation of the Phase-Iconstruction. Due to a tight construction schedule, 14 Tunnel Boring Machines have been deployedto 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 tointroduce the methods employed to overcome the rock formations encountered during excavationwhile deployed TBM was for soft soil excavation. Through the various tunnelling performance andrelated ground settlement results, several conclusion and recommendation have been deduced forfuture tunnelling works within New Delhi area of India.

INTRODUCTIONDelhi Metro Phase-II is mainly an extension of the Phase-I project which was completed in 2006and consists of the construction of 128km of track, 81 stations and 5 depots. The works comprise94km 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 Indiaand Delhi Government and is scheduled to be operational in time for the Commonwealth Games ofOctober 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 havebeen allocated for a 4.2km stretch of the Badarpur Line and additional four will excavate 3.5km ofthe Airport Line.

The first TBM tunnel started on the Qutab Minar Line on 31st December 2007 and at this point intime 14 TBMs are now in operation. The maximum progress achieved to date by single TBM is 28rings (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 alluviumsoils known locally as the Delhi silts with isolated outcrops of competent quartzite. The quartziteforms a range of low hills known as the Ridge, an extension of the Aravalli Mountains whichextend from the south of the territory to the western bank of the Yamuna River. The Delhi siltswhich 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 thenearly enclosed Chattarpur alluvial basin contains alluvial soils derived from the adjacent quartziteridge.

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Airport Line

Qutab MinarLine

BadarpurLine

Figure 1- Route Map and TBM arrangement for Delhi Metro

New Delhi

MalviyaNagar

Udyog Bhawan

Airport

Lajpat Nagar

Phase-I Line-2

: Airport Line

: Qutab Minar Line: Badarpur Line

Figure 2- Geology of Delhi and TBM Section

TBM Section

Geological Formation

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Figure 3- Typical SPT for Delhi silt

QuartziteThe local quartzite rock has undergone several phases of tectonic activity which has resulted infracturing and folding. These disturbances and fluctuations of the bedrock have resulted in intenseand 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 ofunconfined Uniaixial Compressive Strength (UCS) tests are inconsistent and vary within a rangefrom 20 to 160 MPa.

AlluviumThe Delhi silt encountered along the entire routeand the thickness of the alluvium depositsdepends upon the sub surface bedrocktopography infilling the previous topography.

The alluvium is generally a fine grainedmaterial consisting of gradational variations

between clay and silt with variable fine sandcontent. The soils are occasionally difficult toaccurately describe by visual assessment alonedue to their borderline clay/silt nature. Aconspicuous feature of the alluvium is the

presence of generally coarse sand to medium

occasionally coarsegravel sized buff coloured

calcareous nodules. These are found scattered

throughout the stratum and are locally termedKankar. Although some cohesion has beenobserved, a value of 0 kN/m2 was assumed forstatic calculation and the friction angle wasassumed to vary within a range of 30 to 32degrees.

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 Robbinswith 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 CorporationFor the above machines, the TBM specifications are summarized below;

Table 1- EPB TBMs Specification

Contract BC16 BC18 BC24 AMEL-

C1

AMEL-

C5

TBM Supplier Herrenk-

necht

(HK)

Robbins

with

Mitsubishi

HK HK HK Okumura

TBM Numbers Ps 2 2 2 4 2 2

Drive length/ TBM m 1,990 2,030 3,150 1,920,

2,240

2,200 1,300

Geology Delhi silt,

quartzite

Delhi silt Delhi silt Delhi silt Delhi silt,

quartzite

Delhi silt

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 headsbetween 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 0.61.4

Km of individual drive completion.

TUNNELLING PERFORMANCE AND CASE STUDY

Tunnel Progress

Tunnel progress is related to numerous factors such as ground conditions (including the presence ofground 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-

C1

AMEL-

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.

Full Face Cutter head (BC16, BC18, BC24,and AMEL-C1)

Spoke Type Cutter head (BC16 and AMEL-C5)

Figure 4- Typical Cutter heads of TBMs for Delhi Metro Phase-II

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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.

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 tobe 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 halfis 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 hardrock face, an average 3.9 rings (4.7m) progress per day was attained and mining works were

completed within 20 days for 100m stretch.

(mm)

1 TBMPassing

2 TBMPassing

Date

Figure 5- Surface Settlement by Tunnel Excavation & Cracks observed on wall surface

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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 DelhiMetro 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 aminimum should be employed not only for breaking through tunnel eye at TBM launch and

arrival but also for mining the rock under unforeseen condition.

Figure 7- Temporary shaft and Setting of Cutter face from C855

Figure 6- Typical section (UP Line) of TBM and rock formation at each chainage

CH. 24+000 CH. 23+975 CH. 23+950 CH. 23+915

6540m

m

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3) The ground surface settlement could be managed well under open mode of TBM operation inthe 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 perday) is readily achievable in the Delhi silt formations.

5) Ground surface settlement by controlled tunnel operation is relatively small, namely 5mm to20mm 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 oftunneling works. We also thank Mr. Ravindra Dutta (Tunnel Expert from RITES) and Dr. AteeqKhateeb (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, InternationalMetro Civil Contractors, Delhi

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Documents

Paper on Phase 2 Izumi, Tyagi, Lovelock