Conventional Tunneling in Urban Areas
Conventional tunneling as defined by ITA’s Working Group 19 is often referred to as New Austrian Tunneling Method (NATM); Sequential Excavation Method (SEM); or Sprayed Concrete Liner (SCL). It is being used more often in urban settings, in very soft ground, low cover, and overbuilt conditions for the creation of tunnels, station caverns and cross passages between previously TBM driven soft ground tunnels. To enable open face excavation ground improvement methods are used and include various methods of dewatering, grouting, and ground freezing. The paper examines criteria to be used for the implementation of conventional tunneling in urban areas, impact on existing facilities, ground improvement measures, and risks mitigation measures for conventional tunneling under such circumstances. The paper illustrates these aspects in two recent examples: Chinatown Metro Station in San Francisco and Sound Transit Bellevue Tunnel in Seattle, both very recently and successfully completed tunnels in urban settings in the US.
2019 World Tunnel Congress Conference Proceedings
May 3 – 9, 2019, Naples, Italy (Munfah, N., Gall, V., Klary, W. & O’Brien, T.)
Copyright holds the International Tunnelling and Underground Space Association (ITA).