448 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



Removal of loose and projecting rock from the canyon walls and 

 the excavations for the intake towers, dam abutments, back walls 

 of power house, and the valve house benches were conducted by the 

 spectacular high scaling methods. Ropes were fastened to anchors 

 along the canyon rims and men, suspended from the ropes by safety 

 belts or on bosun chairs, pried off all loose rock and drilled for 

 blasting. High scalers were lowered to their work by cableway 

 or climbed to that position " over the ropes." Approximately 

 930,000 cubic yards of rock were dumped into the canyon by these 

 methods. 



Inclined shafts, from outer diversion tunnels to spillway chan- 

 nels, and the raises to all four intake towers were excavated by 

 first driving a top heading from the lower tunnel upward, enlarg- 

 ing the slot across the section to the invert, and then breaking the 

 sides into the slot, working from the top downward on horizontal 

 benches. Muck was removed from the tunnel below by an electric 

 power shovel and fleet of trucks. Lining the inclines with a 3-foot 

 thickness of concrete progressed from the lower tunnel upward. 

 Concrete was brought to the canyon rim in 4-cubic-yard " agitator " 

 buckets, lowered by cableway or derrick to the upper portal and 

 then placed in position behind steel or wooden forms via zig-zag 

 chutes or by lowering the " agitator " by rail down the incline invert 

 to a belt conveyor which carried the concrete to the forms. Linings 

 of the penstock tunnels and the horizontal sections of the header 

 tunnels were placed by means of conveyor belts or " Pumpcrete " 

 guns. 



Concrete for the intake towers was placed by 15-ton derricks 

 equipped with 180-foot booms which took the loaded bucket from 

 train or cableway platform and lowered it to a centrally located 

 hopper on the tower. From here the concrete flowed to place 

 through radially located chutes. A similar arrangement was em- 

 ployed for building the power house and valve houses, cableways 

 being used in place of derrick. Equipment for lining the spillway 

 channels and constructing the weirs consisted primarily of train, 

 truck, and cableway for transportation in 4-yard buckets from the 

 Hi-Mix plant, and a dragline equipped with an 100-foot boom for 

 conveying the concrete by 1-yard bucket to the pouring site. 



But it was in the huge mass of the dam that the cableways, mixing 

 plants, and transportation facilities received full play. Concrete was 

 loaded into 8-cubic yard bottom dump buckets and transported to 

 pouring site first by train, consisting of a compartment car pulled 

 by an electric or gasoline locomotive, and then by one or another 

 of four 25-ton cableways. On June 6, the first bucket of concrete 

 was dumped for the huge structure of the dam. Six months later 



