ABSTRACT
Rapid population growth and economic expansion are creating significant challenges for large cities and metropolitan areas. Developing underground spaces offers a solution to meet infrastructure demands without disrupting existing surface land use or causing substantial environmental impact. By utilizing subterranean areas, cities can accommodate growth while minimizing disturbances to the urban landscape. Additionally, underground metro systems provide an effective means of transportation for city dwellers, helping to reduce their environmental footprint in densely populated urban centers. Conventional Cut-and-Cover techniques for constructing metro stations demand extensive land areas, which poses a significant challenge in densely populated urban environments. To address this issue, the Pune Metro project implemented an innovative hybrid approach. This method combined open cut shafts with large NATM tunnels to mitigate land scarcity concerns. This paper explores the construction methodology and benefits of this technique. Key observations during the underground metro station construction include: i) The approach requires substantially less surface area compared to traditional cut and cover methods. ii) The vertical shaft serves dual purposes, facilitating passenger movement and housing essential facilities like Battery back rooms and Signaling & Telecommunication rooms. iii) Environmental impact is notably reduced due to limited surface excavation. iv) The use of NONEL double delay detonators in conjunction with emulsion explosives kept blast-induced ground vibrations below 10mm/sec. v) This method led to significant improvements in construction speed and cost-effectiveness. The insights gained from this project will prove valuable for future metro station construction in confined, densely populated urban areas with mixed ground conditions, particularly regarding methodology, challenges, and mitigation strategies.
