PICNIC AT HANGING LAKE

This article describes the construction of the Hanging Lake Tunnel in Glenwood Canyon, CO, USA, which has completed the Interstate 70 highway which runs east-west across the USA. The whole four-lane highway and the tunnel are now fully used ahead of schedule. The 4000ft long tunnel not only relieves congestion on the highway, but enables the old road to be used solely for visitors' enjoyment of a scenically attractive recreation area. Both ends of the tunnel are approached above ground level. The east portal is approached via the Hanging Lake Viaduct. This is a 7000ft concrete segmented bridge. The west portal is approached over a 1200ft steel girder bridge. The tunnel set various records: (1) it was completed a year ahead of schedule; (2) it used new tunnelling equipment and support systems; (3) its ceiling cladding was done faster than usual; and (4) its cost was almost $15 million less than the estimated cost. Innovations in the equipment for the tunnel's drill and blast procedure included: (1) the Rocket Boomer, a prototype drill rig from Atlas Copco; (2) the structural support, where shotcreting and rock bolts were used instead of steel ribs; and (3) the use of a robotic arm for shotcreting. The tunnel uses automated lighting, to accommodate outside light levels, and a wide variety of high- technology monitors and sensors. Their operations are controlled continually from an underground complex.