Technical Challenges Faced During Underpassing of Tunnel Line-8 beneath Line-2 Tunnel by TBM at Hauz Khas
Alignment of Magenta Line i.e. Line-8 from Janakpuri West to Botanical Garden corridor of Delhi Metro is crossing the operational yellow line of corridor Huda City Center to Jahangirpuri near Hauz Khas station, which is an interchange station for both the lines. Clear cover above the tunnel of the yellow line is about 11.97m, hence, it was not possible to accommodate the alignment of Magenta Line above the yellow line. Therefore, it was decided to construct the new tunnels beneath the operational yellow line tunnels. Designing the TBM drive below the existing tunnels of Line-2 was a challenging task. Main objective was to control the settlement of operational tunnels and to establish a monitoring system for the construction. So, the design of the Under passing of tunnels was done keeping in the mind, the expected settlement and angular distortion of existing twin bore tunnels, to assess the width of plastic zone formation around the new tunnels, propose construction parameters for TBM to minimize interaction with existing structures so that settlement is minimized, establish trigger and alarm values of settlements and to propose a real time monitoring and instrumentation scheme. 1.