THE WORLD’S LARGEST UNDERWATER TUNNEL runs beneath the river Mersey between Birkenhead and Liverpool. On either side of the river the tunnel has two entrances, the subsidiary tunnel having an internal diameter of 26 feet. The main tunnel, which has an internal diameter of 44 feet, has a length of 3,751 yards. The width between the kerbs is 36 feet, sufficient for four lines of traffic. The ventilation of this huge tunnel, through which 4,150 vehicles an hour can pass with intervals of 100 feet between them, was a complicated problem. Six enormous ventilating stations were built, three on either side of the rive, to house the gigantic fans.
Building the Boulder Dam (photogravure supplement)
Building the Boulder Dam 1
THE TASK COMPLETED. While a huge reservoir is forming above the dam, water escapes through twelve valves, six on either side of the canyon, to maintain the steady flow of the river below the dam. This water falls into the river from a height of 180 feet, 13 feet higher than Niagara Falls. At the foot of the dam is the power house, and in the foreground are the openings of the tunnels through which water was diverted while the dam was being built.
Building the Boulder Dam 2
THE FOUNDATIONS OF THE DAM were laid 139 feet below the normal water level of the Colorado River, shown by the positions now occupied by the bases of the intake towers (see photo below). Some 3,400,00 cubic yards of concrete were used in the building of the dam, and this enormous volume of material was mixed in two plants near the site of the dam. In the right foreground is the spillway on the Nevada side of the river. The network of specially built roads, bridges and cableways gives some idea of the size of the undertaking.
Building the Boulder Dam 3
SECURING ANCHORAGES from which drillers swung by ropes during the early stages of the work. Hanging hundreds of feet above the river, on the precipitous walls of Black Canyon, gangs of men worked for many months through the terrific heat of summer, drilling, blasting and fixing anchorages for cableways and suspension bridges.