Chennai Metro Rail (CMRL) begins retendering for the outstanding balance of construction of the twin running tunnels and three underground stations that make up the critical UAA-02 Contract at the heart of the Indian city’s new metro system.
Additionally a 2.4km design-build underground extension between Washermenpet and Korukkupet (Contract UAA-08), including construction of two underground stations, is also released for tender. Bids are due to be opened in the coming weeks. The balance of the new 9km extension as far north as Wimco Nagar will be elevated.
Construction of the 18km of twin running alignment and 19 underground stations of Phase I of Chennai’s metro system is divided into five station and running tunnel lots (UAA-01–UAA-05). The system also includes a further 20km of elevated track in the east of the city and south to the airport.
A mixed geology comprising soft ground and sand, through transitions with clay, weathered and fractured rock, hard granite, gneiss and boulders, all through a high groundwater level, have proved challenging for the 12 TBMs (8 x Herrenknecht EPBMs, 1 x Robbins EPBM, 2 x STEC EPBMs and 1 x Hitachi EPBM) procured for the project (Table 1).
The schedule of underground works was thrown into disarray in May last year (2015) when the Russian contractor Metrostroy walked off Contract UAA-02 (the 3,616m May Day Park–AG-DMS section using 2 x Herrenknecht EPBMs), half way through the job. Its joint venture partner Gammon (India) had been constructing the stations.
|Table 1. Progress on Chennai Metro Phase 1 (underground sections)|
|Package||Contractor||TBM||From||To||Length (m)||Complete (m)|
EPBM x 1,
HK EPBM x 2)
|3||May Day Park||Central||1040||1040|
|3||May Day Park||Central||1040||1040***|
(HK EPBM x 2)
|1||May Day Park||AGDMS||3616||1835|
|2||May Day Park||AGDMS||3616||1700|
(HK EPBM x 2)
(STEC x 2,
(HK EPBM x 2)
* Contract to be retendered as BW-UG-02 (stations) and BW-UG-02 (tunnels)
** Contract retendered as BW-UG-03 to L&T (stations) and Afcons (running tunnels)
*** Breakthrough 27/1/2016 (TBM remains under soil at base of reception shaft)
At the same time, Metrostroy walked away from its joint venture with Gammon on the further advanced Contract UAA-03 (the 3,300m Saidapet–AG-DMS section using 2 x Herrenknecht EPBMs). The Russian contractor left behind construction equipment and materials valued at several million dollars, including all four TBMs it had procured for excavation of the running tunnels on both contracts, and walked off site after failing to reach agreement with CMRL over escalating costs. TunnelTalk posed a number of written questions to both CMRL and to Metrostroy regarding the cancellation of the contracts, but had received no reply prior to going to press.
After cancelling Contract UAA-03, and cashing in the contractor’s bank guarantee of approximately US$15 million, CMRL awarded the balance of tunnelling works to Afcons, which had already completed the running tunnels of Contract UAA-05 (the 2,797m section between Shenoy Nagar–Thirumangalam using 2 x Herrenknecht TBMs) in JV partnership with Transtonnelstroy Limited of Russia.
The balance of construction on Contract UAA-03 of four stations and the cut-and-cover ramp south of Saidapet Station for grade level connection towards the airport, was taken over by Larsen & Toubro (L&T), which had already completed Contract UAA-04 (the 3,400m Egmore–Shenoy Nagar section, using 2 x STEC and 1 x Hitachi EPBMs) in joint venture partnership with Shanghai Urban Construction Corporation (SUCG).
With the abandoned UAA-03 section 90% complete at the time it was retendered by CMRL as Contract BW-UG-03, breakthrough into AG-DMS Station with the first TBM was achieved by Afcons on 4 July (2015), with final breakthrough on the parallel drive achieved at the same location on 1 September (2015).
Meanwhile, the Afcons Infrastructure Limited (India)/Transtonnelstroy Limited (Russia) JV is currently well advanced towards final breakthrough on Contract UAA-01, comprising a 4,445m section between Washermenpet–Egmore using 2 x Herrenknecht, and a 1,040m southbound run between Central Metro and May Day Park using a single Robbins EPBM.
At the end of last month (January 2016) the Robbins EPBM broke through the diaphragm wall at the bottom of the west reception shaft at Central Station, for final completion of the second and final parallel running tunnel between Central and May Day Park. The same machine completed the parallel tunnel in July 2014, but suffered severe disc cutter wear as a result of mixed face conditions comprising weathered and fractured granite, through to granite of 150 MPa. In order to make the return drive more efficient, Robbins India provided a geologist to carry out full face mapping, on a daily basis, in both hyperbaric and open mode conditions.
The latest breakthrough, however, is hidden from view because soil at the bottom of the shaft remains to be excavated before the cutterhead can be lifted out. Meanwhile, dismantling of the back-up gantry and running gear back through the running tunnel is under way.
This then leaves the partially completed UAA-02 section, for which the running tunnels are not quite 50% complete, and for which construction of the three underground stations at Government Estate, LIC and Thousand Lights are further behind.
According to contract documentation inspected by TunnelTalk the running tunnels between May Day Park (just north of Government Estate Station) and just north of AG-DMS Station remain to be excavated. Project data supplied by CMRL shows that the first Herrenknecht EPBM had completed 1,835m of its 3,616m drive at the time the previous contractor walked off site, while the second Herrenknecht machine is slightly further behind on the parallel drive, at 1,700m. Ground treatment has been completed for five of the 11 cross passages.
Interest in taking over the half-finished UAA-02 Contract, now being retendered as Balance of Works Contract BW-UG-02 (Stations) and BW-UG-02 (Tunnels), has been expressed by L&T and Afcons – both of which have been involved in other underground construction lots of Chennai Metro – as well as by the Hindustan Construction Company (HCC) and Coastal Projects Ltd.
However, the severe flooding that brought chaos to Chennai in December (2015) also resulted in inundation of the incomplete running tunnels and means that the new contractor will have to repair both of the TBMs – one of which was already damaged, and both of which will require all their electrical components repaired or replaced as a result of water damage.
The above four construction companies have also expressed interest in bidding for the new underground extension (Contract UAA-08), along with Tata, Solentache Bachy, SUCG and Soma.