Construction crews hit water on July 6 while digging 600 ft below Lake Mead in southern Nevada for the third “straw” water tunnel. The incident, which was not life-threatening, will delay the project’s progress by months. Vegas Tunnel Constructors LLC––a joint venture of S.A. Healy Co., Lombard, Ill., and Impreglio S.p.A., Sesto San Giovanni, Italy ––won the $447-million design-build contract in March 2008. On June 28, an underground fault breached, causing water seepage for four days and making work in the tunnel impossible. Workers were building a 100-ft-long starter shaft for the $25-million Herrenknecht 1,500-ton tunnel-boring machine for a 20-ft-dia,
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.