Breakthrough by the Metrostroy/ERA Infra joint venture into the headwall at Lai Quila Station completes TBM tunnelling on the Kashmere Gate–Jama Masjid (Contract CC-07) section of Delhi Metro’s Phase III Line 6 Heritage (Violet) Line.
The milestone is reached using one of two Terratec EPBMs procured by the contractor JV for completion of parallel drives of 1,350m between Kashmere Gate and Lai Quila; and of 650m between Jama Masjid and Lai Quila.
Only the 1,400m section between Delhi Gate and Jama Masjid – part of the delayed Contract CC-05 which suffered a TBM breakdown that has required excavation of a recovery shaft in front of a city cinema – now remains before all tunnelling is complete on the 9.37km-long underground section (Central Secretariat–Kashmere Gate) of the Heritage Line.
The latest breakthrough at Lai Quila Station on 4 February (2016) marks completion of a 1,352m drive that launched out of the Kashmere Gate shaft at the northern end of the line on 4 April 2015, for an average weekly excavation rate of 31.2m. The installed segmental lining comprises 970 rings of 1.4m in length x 275mm thick.
During the excavation the contractor JV managed the EPBM through a section underneath the elevated station at Kashmere Gate where the distance between the tunnel crown and the piles of the structure above was just 80cm. The alignment also passes under a number of historic buildings and monuments including the Dara Shikoh Library, Lothian Bridge on the Delhi–Shahdara Northern Railway Line, The Grand Post Office, St. James Church and the Kashmere Gate Monument.
The parallel upline was completed by another Terratec EPBM on 3 August last year (2015), while the upline and downline of the Jama Masjid–Lai Quila section were completed in December and July 2014 respectively.
Excavation of the Heritage Line is split into three contracts. The southern tunnel section between Central Secretariat shaft and Mandi House Station, including construction of cut and cover stations at Janpath and Mandi House (Contract CC-01), was awarded by the Delhi Metro Rail Corporation (DMRC) to the Prabibha/CRFG JV. It completed the last of its four drives, using two Herrenknecht EPBMs, in 2013. This section was opened to service in June 2014.
The 3.25km-long central tunnel section between Mandi House and Jama Masjid, including cut and cover stations at ITO, Delhi Gate and Jama Masjid (Contract CC-05), was awarded by DMRC to the Larsen & Toubro (L&T)/SUCG JV. It has completed excavation of the Mandi House–Delhi Gate section, which is operational as far as ITO Station. The JV procured three TBMs – two manufactured by Mitsubishi and one by STEC – for completion of a total of six drives.
Prior to launch in July 2013 of the STEC-manufactured TBM for the first of the parallel 1,070m long Jama Masjid–Delhi Gate drives, contractor SUCG announced that it expected this section would be the most difficult of the whole contract. This was on account of a mixed face geology, a complex urban environment above the alignment, and a challenging owner stipulation of a maximum 3mm ground settlement.
About half way into the drive the TBM broke down, necessitating the excavation of a recovery shaft in front of Golcha Cinema. After more than two years of zero progress that machine has since been extracted and repaired and is expected to relaunch in the coming weeks from the shaft at Delhi Gate Station for completion of the drive from the opposite direction and back into the recovery shaft.
DMRC reports that 20 of the 35 TBMs procured for excavation of 37km of twin running tunnels along the various corridors of the total 140km of new alignment for Delhi Metro Phase III, are still in the ground.