ABSTRACT
Construction of Shaft 17B-1, a part of the New York City water supply’s system Tunnel No. 3 required the excavation of approximately 38m (123ft) of water bearing overburden soil and 160m (527ft) of gneiss bedrock to make a connection to Water Tunnel No. 3. Ground freezing was specified as the method to provide temporary earth support and ground water control for the overburden material. The specifications required the placement of a temporary liner as the frozen earth was excavated. This paper describes the various approaches that were evaluated to determine a technically feasible, cost-effective lining approach. It further describes a comprehensive method of evaluating the frozen soil that ultimately led to the elimination of the temporary liner facilitating efficient and safe excavation of the shaft. Design, construction, and excavation methods are discussed.
