Crossing of tunnels between the piles of operational metro station

This paper is a case study of crossing of Delhi Metro's Line-7 tunnels between the piles of operational Line-6 Lajpat Nagar Metro Station. The pile foundations of existing station which were falling within the zone of influence of the tunnels were likely to get affected by the tunnelling and construction activities. To keep lateral deflection of pile and ground settlement under acceptable limit, it was necessary to reduce the effect of vibrations generated during TBM operation and movement of piles induced due to tunnelling. To reduce the mentioned effects, contiguous RCC piles were casted in front of existing piles of Lajpat Nagar metro station. The casted curtain of RCC piles reduced the lateral deflection and ground settlement under acceptable limit. Also to reduce vibra-tions, TBM speed was reduced while passing existing station. An extensive instrumentation monitoring system was placed adjacent to piles, piers and station structure to ensure safe working. This monitoring was covered on a 24 hour, 7 days basis by two shifts of moni-toring team.