Shaft, Cavern, and Starter Tunnel Construction for Lake Mead Intake No. 3: Temporary Support and Permanent Lining Solutions

摘要

In March 2008 Vegas Tunnel Constructors (VTC), a joint venture of Impregilo SpA and SA Healy were awarded a 447 Million US dollars Design-Build contract by the Southern Nevada Water Authority (SNWA) for a sec?tion of the Lake Mead Intake No. 3 Project. Arup, supported by Brierley Associates, is the Design Engineer for VTC. The VTC contract scope of new facilities for Intake No. 3 includes three major components: a deep tunnel access shaft and cavern, a tun?nel beneath Lake Mead, and a submerged intake structure. The first major construction phase of the project is nearing completion. Construction of the 9 m diameter 185 m deep access shaft was com?pleted using a drill-and-blast top-down construction method, with a 450 mm thick unreinforced concrete final lining placed as excavation was completed. The shaft passed through a major fault zone and discontinuity swarms requiring extensive pre-exca-vation grouting for water control in portions of the shaft.