Ground Conditions Encountered and the Support System Installed in the Realigned Starter Tunnel for the Lake Mead No.3 Intake, Nevada

摘要

In 2008 the Southern Nevada Water Authority (SNWA) awarded Contract No. 070F 01 C1 for Lake Mead Intake No. 3-Shafts and Tunnel to a joint venture between Impregilo SpA and SA Healy, the Vegas Tunnel Constructors. Following award, the 9m diameter, 185m deep access shaft and 20m wide, 10m high and 50m long TBM launch chamber were successfully constructed. Difficult conditions encountered in the original starter tunnel during 2010 resulted in its abandonment and sealing in early 2011. Vegas Tunnel Constructors commenced excavation of a realigned starter tunnel thereafter to allow the installation and erection of the 7.22m diameter 190m long Herrenknecht AG Dual Mode Mixed Shield TBM. This paper describes the ground conditions encountered during the excavation of the realigned starter tunnel, discusses the excavation production data and summarizes the support system employed to successfully complete the starter tunnel.