Delhi Metro Rail Corporation has begun the lowering work of first-ever Tunnel Boring Machine (TBM) of Phase 4 project work at Vikaspuri on Janakpuri West-RK Ashram Marg corridor. Two tunnels (for up-down movement) of 1.4 kilometres will be bored as per the tunnelling drive, DMRC said in a statement. Tunnelling work with TBM is expected to start next month.