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the latter extending over the lock site from opposing movable steel towers. There were four duplicate cableways in the concrete-placing plant and two duplicate and one simplex in the unloading plant. An auxiliary mixing plant of two 2-cubic-yard mixers was also used, and concrete from it

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was delivered by cars on a narrow-gage railway running through the locks. In all 2,085,000 cubic yards of concrete will be placed at Gatun. The estimated cost per yard was $7.75

and when the work was only 60 per cent completed this had been reduced to $6.70 a yard.

The locks at Pedro Miguel consist of a single flight or step of twin locks, two in all, by which a drop of 30 feet,

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from Culebra Cut to Miraflores Lake, or a reverse lift, is Pedro Miguel

accomplished. They are built through a hill,

on rock, and 1,150,000 cubic yards of excavaand Miraflores Locks.

tion were required for the emplacement.

The total amount of concrete required is 837,500 cubic yards.

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MIRAFLORES LOCKS, DAM, AND SPILL WAY. Miraflores Locks are located in low ground, the river bed of the Rio Grande, and yet are on solid foundation. The emplacement required five million cubic yards of excavation. There are two flights or steps of twin locks, each step representing a lift of 273 feet, a total lift of 55 feet. all 1,362,000 cubic yards of concrete are required. At the lower or sea-level locks in this flight it has been necessary to anticipate the great differences in pressure due to the variation of 20 feet between high and low tide; and because of this difference these locks are the largest on the canal in point of depth, the maximum lift being nine feet more than in the sea-level locks at Gatun. The lower gates at Miraflores are 82 feet high.

The rock for concrete at Pedro Miguel and Miraflores is quarried and crushed at Ancon Hill, a few miles from the

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lock sites, and the sand is dredged at Chame beach a few miles west of the Pacific entrance to the Canal, whence it is carried in barges to Balboa and by train to the locks. The cost of concrete runs from $4.50 to $6.00 a cubic yard. At both locks the materials are taken from storage piles by cantilever cranes and mixed into concrete within the body of the cranes, whence it is hauled in cars to any part of the locks, to be placed by other cantilever cranes.

Dams.

There are three dams on the Canal-one at Gatun and one at Pedro Miguel, to hold the water of Gatun Lake at 85 feet above sea-level; and one at Miraflores to hold the water of Miraflores Lake at 55 feet above

the sea.

The dam at Gatun, closing the valley of the Chagres River, extends from the hills

on the east to those on the Gatun Dam. west of the valley, is 11 miles

long, 115 feet high, and tapers from 2,500 feet broad at bottom to 100 feet at the top.

The process of construction is to dump spoil from the canal excavation in two parallel ridges clear across the valley. Between these ridges suction dredges pump a light clay from the river bottoms nearby. This clay hardens as the water drains out, and forms a core that can not be penetrated by water. Halfway across the valley the dam encounters a small hill rising about 120 feet above sea level, and through this the spillway, an opening 280 feet wide, was located because it offered a rock foundation with little excavation. The purpose of the spillway is to regulate the surface of the water in the lake, and to this end sluice-gates are erected on a concrete foundation, by the opening of which

CROSS SECTION OF GATUN DAM. Showing Earth and Rock Fill, Water Boşne Fill, Rock paving on lake side, and surface of Gatun Lake.

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the lake can be kept constantly at any given level, no matter how severe the rains may be in the lake region.

At the spillway there is an intake for water which will be passed through culverts to a power house below the regulating works, where it will turn turbines that will generate

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Showing concrete dam with crest on a curve, Hydraulic Power Plant and Intake. enough electricity to run all the machinery on the canal, operate the Panama Railroad, and light the whole Canal Zone.

The Pedro Miguel Dam is an earth-fill with puddle core, which extends from a hill west of Pedro Miguel Locks to

the locks, and keeps the water of Gatun lake Pedro Miguel at a level of 85 feet above mean tide. It is and Miraflores 1,700 feet long and the top is 105 feet above

Dams. sea level. A similar office is performed at

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