Conventional Tunneling in Difficult Grounds
Conventional tunneling as defined by ITA’s Working Group 19 is being used more and more in difficult grounds. This occurs in rural settings for tunneling through shear and fault zones and in squeezing ground conditions where tunneling by TBMs would be risky, as well as in urban areas in soft ground, under low cover, and in overbuilt conditions or for the construction of subway station caverns, highway tunnels, and cross passages between TBM driven tunnels. To enable open face excavation ground improvement methods are used and include various methods of dewatering, grouting, and ground freezing. This paper provides a preview of ITA’s WG 19 upcoming report on the implementation of conventional tunneling in difficult grounds and it portrays examples from recent projects including cross passage construction for Sound Transit’s University Link and Northgate Link in Seattle and for San Francisco Central Subway Chinatown Station.