Shani Wallis, TunnelTalk
Three TBMs, a NATM mined station, open-cut stations, and sections of open-cut tunnelling will shape Line 2 of Delhi's new metro system. In a recent visit to India TunnelTalk visited the project.
The Chawri Bazar area where bored running tunnels and a NATM mined station are needed
- Delhi has made a determined start on its ambitious plans to bring modern mass transit services to its 13.8 million residents. Construction of the first three lines (62.5km) of an ultimate 198km network was sanctioned in 1995 with the US$997.8 million investment (1996 estimate excluding inflation) programmed over a 10-year period to have all three lines operating by September 2005.
- Of the initial three lines, all of Line 2 at 11 km long is underground and has 10 underground stations. Line 1 is either at-grade or elevated, as is most of Line 3 after a 2km long underground section in the central Connaught Place area Construction started on Line 1 in Oct/Nov 1998 and services on the first 8.5km section are scheduled to start in Dec 2002. Work on Line 2 has also started, following the award of two contracts in early 2001(Table 1), and Line 3 is in design for an anticipated invitation to tender in April/May 2002.
- Table 1. Contracts let for design-build procurement of Line 2 and system-wide installations and under the Japanese Bank of International Co-operation project funding.
- methods of construction then divided the Line into two rather than one large contract. The 4.5km MC1A northern section with four stations is designed as open cut, including running tunnels. The 6.5km MCIB southern section requires bored tunnelling with a 1.4km section of open cut possible from Patel Chowk to Central Secretariat stations. Of the six stations five are open cut with one beneath the Chawri Bazar that will be mined.
Planned network for Phase I and Phase II
International design-build procurement for Line 2 was part of the project's funding arrangements. Some 56% of the Phase 1 project is financed through a soft loan agreement with the Japan Bank of International Cooperation (JBIC) with 30% funded through equal equity contributions from DMRC's two government stakeholders; the central government of India and the state government of Delhi. The remaining 6% raised through property development opportunities along the lines. The JBIC funding is not a tied loan explained Sreedharan, but "required that the project be reviewed and supervised by an international consultant, and that the Line 2 contracts be open to international bid, and construction procured under design-build contracts. The World Bank and Asia Development Bank were also interested in the project but JBIC offered the most favourable terms and made funds available within the shortest lead time."
- To comply with the first requirement, the consulting JV of Pacific Consultants International of Japan (leader), Parsons Brinckerhoff International (USA), Japan Railway Technical Services, Tonichi Engineering Consultants (Japan), and the Rail India Technical and Economic Services (RITES) was appointed General Consultant in September 1998. Prior to that, RITES, the engineering company owned by India's National Rail Corporation, had managed development of the metro.
- "As General Consultants we reviewed all existing design and contract documents for the system and we are managing design for all of Line 2 and for 2/3 of Line 1" explained Tony Burchell, Project Director for the JV. "30% of the design was completed for the design-build contracts on Line 2 and we assisted DMRC in tender evaluations and contract awards. We are now checking detailed designs submitted by the design-build contractors and will supervise construction of these. We will also assist DMRC in management of the project as a whole."
- "International involvement on Line 2 was required to ensure employment of the latest hi-tech tunnelling methods," explained Mangu Singh, Chief Project Manager for Line 2. "Several cities in India are considering new metros but the only experience to date has been the Calcutta Metro. That project encountered well-reported problems. So for Delhi we had to improve on all aspects of the process."
- Nine groups pre-qualified for the Line 2 design-build contracts. Three proposals for the bored tunnels contract MC1B and two for the MC1 A open cut contract were received in February 2000. "All five technical proposals were accepted," said Singh, "but the financial bids were all considerably higher than estimated." Original estimates were based on the Calcutta Metro, designed back in the early 1970s under conventional design-bid-build contracts. Thirty years on Delhi has a much higher specification. Nevertheless, cost proposals were too high and after negotiation were reduced by various methods including the relaxation of some specifications such as allowing sheet piling instead of rigid walls to support open-cut running tunnels.
Fig 1. Geological section of the 11km long Line 2 alignment showing the geological anomaly that will present difficult mixed ground conditions at the NATM Chawri Bazar station
- The two contracts were eventually awarded in February 2001. The 50-month MC1A package for the 4km long open cut section from Vishwa Vidyalaya to the Interstate Bus Terminal (ISBT) with a contractual end date of July 2005 was awarded to the KSHI JV between Kumagai Gumi (Japan - Leader), Skanska (Sweden), Hindustan Construction (India), and Itochu Corporation (Japan), with contract engineer Maunsell (Australia). The 60-month MC1 B package for the 6.5km long bored tunnel section from ISBT to Central Secretariat was awarded to IMCC comprising Dyckerhoff & Widmann (Germany - Leader) with Shimizu Corporation (Japan), Larsen & Toubro (India), Samsung (Korea), IRCON International (india) and with contract engineer Mott MacDonald (UK).
- Notices to proceed were issued in April and May 2001, and a 39-week period of definitive design started on-site in October.
To complete the bored tunnels on contract MC1B, IMCC has bought three Herrenknecht TBMs - two EPBMs and a hard rock shielded machine. Delhi is built on the water-bearing silts of the Yumuna River flood plane that overlay a highly variable rock interface with 3.5bn year old, very folded, highly weathered quartzite and veins up to 2m thick of Mica Schist to a compressive strength of 100-250MPa. At an average depth of 15m below surface, the Line 2 tunnels pass through soft wet soils beneath the water table at 4-6.5m below the surface and harder rock strata. On MC1A, KSHI requires dewatering between sheet piled retaining walls and shotcrete and rockbolts to support drill-blast of hard rock sections of the open-cut tunnel alignment.
- Delhi is located on the Himalayan foothills and seismic loading design criteria is Category 4. Survey, monitoring, and protection measures to control settlement damage are also important design and construction concerns. The underground alignment passes beneath several protected structures as well as two of Delhi's main railway stations.
Two EPBMs assembled for launch at Patel Chowk Station box
- The two Herrenknecht EPB machines for Contract MC1B were first used for the Bangkok Metro in the late 1990s. The TBMs are now being refurbished in India under Herrenknecht supervision and are due to arrive on site in May 2002. The third machine, a new Herrenknecht rock machine, arrived in Delhi in January 2002 and all three are scheduled to start boring in June/July 2002.
- The TBM tunnels are lined with precast concrete bolted and gasketed segments designed by Mott MacDonald. There are five segments and a key in each 1.2m wide x 5.7m id x 280mm thick segmental ring. IMCC has established an off site casting yard, equipped with 72 moulds supplied by CBE of France and production is to start in March 2002.
- Bored tunnelling was also an option for the open cut works on contract MC1A but as Hisayoshi Yoshikawa, Project Leader of the KSHI JV explained: "To make it worth while, tunnelling would have to be used for the full 4.5km of the contract and that would have required two of each TBM type - hard rock and soft ground. NATM excavation of the running tunnels through the 900-1,200m rock section was also possible but again the length is too short. The options were just uneconomical when compared to open cut."
- During the TunnelTalk tour of Line 2 sites in December 2001, KSHI had started necessary traffic and utility diversions ahead of open cut excavation and sheet piling had started. Diaphragm walling for two of the four stations as well as core excavation was due to start in February 2002. Work will progress 24hrs/day, 7 days/week with restrictions on various activities such as muck haulage at peak hours and sheet piling in the hours from 9pm to 6am.
- For IMCC on contract MC1B, work has also begun to install diaphragm walls for open cut station works ahead of core excavation and TBM launch. Project Leader Sternath pointed out three particular techniques being used on the project to ensure top quality construction.
- First, each diaphragm wall panel is surveyed using the Koden system. An ultrasound scanner is lowered and raised slowly into the 6m long x 800mm wide x 20m deep slurry-filled trench and the profile of the wall is printed. This allows any underbreak or fall out in the bottom to be re-excavated before the reinforcement cages are inserted is a vertical waterproofing seal inserted between the panels of permanent diaphragm walls. A PVC waterproofing membrane will seal the roof slabs of the stations.
An initial plan for NATM excavation of Chawri Bazar Station
- Thirdly, the BARTEC coupling system for creating links between rebar cages in the vertical walls and the horizontal reinforcement of invert, intermediate and roof slabs. A method of cold forging increases the core diameter of the rebar to take the threaded ends of the joint without reducing the bar's cross section. No torque wrench is required and the splice is stronger than the rebar guaranteeing full ductile elongation of the reinforcement without joint failure.
- At Chawri Bazar TunnelTalk visited one of two small sites where access into the NATM mined station below will be excavated between permanent diaphragm walls. The station is designed by Mott MacDonald as three 288m long interconnected caverns of up to 70m2 slightly larger at fan locations, comprising twin platform tunnels and two large shafts housing ventilation plant, elevators, escalators and furnishings for concourse areas. In addition to the logistical for challenges in this incredibly crowded area of delhi, excavation of Chawri Bazar station is further complicated by geology. A deep incision of water bearing alluvium cuts into the more competent weathered quartzite and schist right at the location of the proposed NATM station.
All three lines of the Delhi Metro Phase 1 are new rights of way, acquired at about 8% of the project cost by DMRC, using an interest-free subordinate loan from the central and state governments. Securing the alignments, clearing the sites governments.
- Securing the alignments, clearing the sites and resetting has been without incident. "Once the Calcutta Metro was finally opened, people took to it very well," said Singh. "Passenger numbers are high and there is little vandalism. Here in Delhi too, people have been waiting for the metro for 20-30 years. There has been a change in public attitude, a highway bridge usually takes 7-10 years to realize in Delhi, but the metro viaducts on Line 1 have been completed in 2-3 years. The metro fare and we are expecting up to 2.2m commuters/day on Phase 1 when it opens fully."
The underground alignment of Line 2 interconnects with the elevated alignment of Line 1 at the ISBT - Interstate Bus Terminal Station and with Delhi Main and New Delhi railway stations
- Under further contract considerations, all sites are within 2m high hoardings; muck disposal routes are identified by traffic police noise levels of generators, compressors and other machines must be limited, and the cutting of trees on-site is strictly controlled.
- Tunnel boring on contract MC1B and rock excavation and civil works schedule on KSHl's open t contract are the project's critical paths. To meet IMCC's 60-month MC1B contract period, an optional TBM may be specified. "We have scheduled to e tunnelling with three TBMs but if necessary, we have an agreement with Herrenknecht for a fourth" said Sternath for IMCC.
- In accepting the challenge to meet the September 2005 opening date for Line 2, the two design-build contractors have something to prove to DMRC. Sreedharan is not fully convinced of advantages purported by the design-build procurement method. "There are a lot of uncertainties associated with metro design and underground excavation" said Sreedharan, "and the full risk of these is diverted from the owner to the contractor under design-build. Different issues influence programming and decision making when design and construction are within the same organisation. Many of these risks should stay with the client in my view, but having inherited the situation when I moved to DMRC, I will have the experience of managing both conventional designbid-build and design-build contracts on Phase 1."
- Prior to DMRC, Sreedharan was managing director of the Konkan Railway Corporation. As a civil engineer and career employee of India Railways, Sreedharan was persuaded at 70 to remain out of retirement and take up directorship of DMRC for the crucial first years of its operation.
- The Konkan Railway was procured under the Corporation's own project management, through conventional design-bid-build contracts. The same model is being used for procurement of lines 1 and 3 of the Delhi metro. "Design-bid-build contracting on Line 1 has brought the first section to a scheduled opening in December 2002 with the remainder of the 28km line due to open in December 2003," said Sreedharan, "and from awards of contracts in April/May 2002, design-bid-build of the 23.5km long Line 3, is scheduled to open in September 2005." Although Sreedharan would have "preferred designbid-build for the Line 2 contracts" the goal was to make the design-build concept in place work.
- In managing the Phase 1 contracts, arbitration through General Consultants rather than disputes review boards (DRBs), has been selected. "Arbitration is a very just and fair method of hearing grievances. We have a negotiating team in DMRC and arbitrators are appointed from an approved list for each case. It is on the performance of the owner that the success of large public works projects like the Metro are judged and on Line 1 where we have finished several contracts, we have illustrated that we will settle disputes fairly and quickly."
- Once in service, passenger fares plus advertising income is expected to repay 95% of the JBIC loan over 20 years from opening of the Phase 1 system. The remaining 5-6% is to come from property development and the liability of any shortfall will rest with DMRC's two government shareholders. For the moment, concentration is on construction.
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