Breakthrough into Palam Station completes the last of four drives for a pair of Terratec EPBMs being used to drive the outer part of Contract CC-34 for the twin running Vikaspuri-Palam section of the Delhi Metro Phase III extension.
Earlier completion of the central drives between Janakpuri West Station and Dashrathpuri Station means the latest breakthroughs by Terratec machines (S36 Jantar and S37 Mantar) mark the successful end of all TBM excavation on the 4.4km-long twin bore section.
The pair of 6.52m diameter EPBMs from Terratec – ordered as part of a four machine, eight drive strategy by the contractor, the Hindustan Construction Company (HCC)/Samsung JV– completed their first 625m-long drives between the launch shaft at Vikaspuri and the cut-and-cover shaft near Janakpuri West Station (Fig 1) in September and October last year (2014).
Terratec reports that the latest and final breakthroughs into Palam Station, following 1,224m drives out of Dashrathpuri Station, took place at the end of August (2015).
The breakthrough ceremony was held in presence of the project owner, Delhi Metro Railway Corporation, and the contractor JV. “We are thankful to all our sub-contractors and equipment suppliers, especially Terratec, as these TBMs have excavated very smoothly and this has helped to complete the works ahead planned schedule,” said Raman Kapil, Project Director for HCC/Samsung.
The contractor selected Terratec to design and manufacture two 6.52m EPBMs with a traditional soil configuration, equipped with a spoke-type cutterhead with a 57% opening ratio.
Excavation of the first stretch started in August 2014 from Vikaspuri shaft and broke through near Kerala school, where a train crossover has been planned for this metro line, completing a short drive of 219m. From there both TBMs were pulled 110m through the crossover area to restart boring a second drive of 354m through to Janakpuri Station. On this drive, the TBMs passed beneath the existing Janakpuri elevated metro station. The distance between the tunnel wall and foundation piles of the existing metro station was only 3m.
The drive between Vikaspuri and Janakpuri stations was completed under moderate pressures of up to 2 bar, through a geology composed of very wet silty clay and sandy soil that is typical for Delhi. Both TBMs passed underneath residential areas and settlement was contained to within less than 1cm.
During the final twin running 1224m-long drives the TBMs passed through very dry soil, requiring the use of a foam injection system for conditioning of the face. During a stretch of excavation beneath the Palam flyover the distance between its foundation pillars and the TBMs was less than 4m. Weekly advances of up to 120m/week were recorded.
A total of eight TBMs manufactured by Terratec have so far excavated more than 12km of metro tunnels over a number of different contracts on Delhi Metro Phase III. All tunneling works will be completed by beginning of 2016.