Surface Settlement Induced by Urban Tunnelling—a Case Study of Mumbai Metro

Mumbai is an elongated island city and spreading towards northern side as the southern side is sea face. Mumbai Metro Line 3 (MML-3) project corridor from Colaba to Seepz, is fully underground metro of a total length 33.5 km twin tunnel. In this project, 17 nos. of TBMs deployed to construct the tunnel. The tunnel is excavated through Basalt underlying filled up material and soil strata (sandy and clayey). A systematic instrument arrays are installed along the tunnel alignment to monitoring at the ground, on the ground and in the tunnel, existing buildings along the tunnel alignment in the influence zone (both side of tunnel alignment) as per monitoring scheme. Monitoring of instruments was done as per the frequency required for tunnelling activities based on the excavation stages and to acquire the recorded data. Based on the monitoring data and their interpretation, design modification has been done to achieve safe tunnelling which is the first and foremost requirement in urban tunnelling. This paper highlights the surface settlement at the ground surface and in the tunnel excavated zone due to tunnelling.