ABSTRACT
As part of Mumbai Metro Line-3, L&T STEC JV, Mumbai is doing design and construction of four underground stations and associated tunnels. Mumbai is one of most crowded cities in the world, where the availability of additional space for TBM shifting from one end of the station to other end is challenging. Hence, TBM drag through was planned at Vidhan Bhavan, Church Gate and Hutatma Chowk stations to achieve the continuous progress of tunnelling. Hutatma Chowk Station is in the heart of densely populated city of Mumbai bearing many heritage buildings on ground surface which are considered as UNESCO World heritage sites. Hence, station excavation was planned to be done partly by cut and cover method and partly by conventional tunnelling. In general, conventional tunnelling is completed with both heading, benching and concrete lining before TBM breakthrough, followed by TBM drag through and relaunch at the other end of the station. This involves a challenge of installing heavy steel cradle and reaction frame in a very limited space. Although conventional tunnelling was started for the station half, as Client mandated to restrict the vibration PPV values, it was impossible to complete conventional excavation before TBM breakthrough. As the completion of balance heading, benching and concrete lining after TBM breakthrough will delay the project progress and cause idling of TBM resources, it was decided to go for this unique methodology of driving and launching TBM inside the conventional tunnel without steel cradle and reaction frame.
