Analysis of the effects of excavation speed, ground condition and tunnel dimension variations on urban tunnel subsidence in Tehran Niyayesh tunnel

The occurrence of subsidence during the excavation of surface-near tunnels, particularly those associated with urban transport systems, is a widespread phenomenon that can lead to significant structural concerns. This study focuses on the Niyayesh tunnel in Tehran, situated within an alluvial region, investigating how variations in excavation speed, tunnel support types, and ground conditions affect subsidence during the intersection of two tunnels with an opening width of thirty-two meters. The support system implemented in this tunnel comprises a latex membrane, a welded wire mesh, and a five-centimeter layer of shotcrete. To assess subsidence, various measurement techniques were employed, including settlement points, convergence pins, geodetic points, extensometer rods, crack meters, and strain gauges. The analysis reveals that the excavation speed and the type of ground influence subsidence rates, which has important implications for future urban tunnel projects and related engineering practices. This research provides valuable insights into the dynamics of surface subsidence in urban tunneling contexts.