Concreting The Calderwood Tunnel
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The Calderwood Tunnel is part of the hydroelectric developement of the same name built bv the Aluminum Co. of America on the Little Tennessee River. The tunnel is 2400 ft long, approximately 26 ft in diameter inside the l2-in. concrete lining, and forms the con-nection between the dam and powerhouse. The excavation from the tunnel, a dense arkose. Was used as a portion of the concrete aggregate. The tunnel was concrete lined in three stages: curb, arch, and invert. A total of 28 000 cu yd of concrete was required for the lining. The coarse aggregate was graded from 3/4 to 3 in. and the sand from 0 to No. 4. The coarse aggregate was produced by crushing the arkose obtained from the quarry and tunnel excavation. The fine aggregate was obtained by passing the 3/4-in. sizes throug two sets of roll crushers. Concrete was brought to the tunnel in 2-cu yd buckets and then dumped into mounted on flat cars. The cars were ulled into t e tunnel by a gas-electric locomotive an d the concrete then discharged into two pneumatic concrete placers which in turn forced theconcrete by air into and through an 8-in. discharge pipe to its final place of deposit in the form. A collapsible Blaw-Knox steel form was used. A 30-ft section was placed every 24 hr. The discharge pipe bends were made of Hagen-White iron to obtain longer wear. Form vibrators were used for consolidating the concrete. Sequence of mixing, transporting and placing was of vital importance as any delay causing a stiffening of the concrete made it difficult to handle.