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ation where feasible. The whole installation is a good example of electric operation.
Realizing that a great deal of the machinery was of new type and that the operating conditions in a tropical climate would be unusually severe, the greatest care was exercised before finally deciding on the type and character of the apparatus. In most cases a sample piece was first made and actually tried out under the severest working conditions, and changed if necessary before the order for the whole lot was given.
The cylindrical gate valves controlling the tunnels from the center-wall culvert consist essentially of a vertical cylinder placed in a chamber adjoining the culvert. The cylinder is seated at the bottom, and directly beneath it is a well to the floor culvert. A short lift gives a large waterway under the edges of the cylinder.
The great advantage of the cylindrical type is that it is very quick opening, and that the water pressures are balanced and do not tend to prevent either opening or closing. On the canal a special form is used which does not involve carrying the full diameter of the cylinder above the water surface.
The larger openings to the main culverts are controlled by rising stem gate valves of the Stoney pattern, similar to those used in the crest of the Gatun spillway dam. The gate is made of heavy structural steel, and the water pressure is taken by a train of rollers at the back of the valve upon which the gate moves. Leakage is prevented by means of a metal water-seal extending around the face of the valve. This seal is fastened to the valve and slides on the wall of the opening and forms the only sliding friction of the whole valve.
Each mitering lock gate consists of two leaves hinged to the walls at opposite sides of the lock, and each leaf is 65 feet long; that is, longer than half the width of the lock, so that when the two leaves are closed, they form an angle pointing against the water pressure. The 92 leaves weigh in the aggregate 60,000 tons, a weight in excess of that of two modern dreadnoughts. If all the gates were laid flat in a pile, it would be 644 feet high.
The joints at the hinges are made water-tight by means of Babbitt metal. Embedded on the sill of the lock is a heavy block of wood, against which a similar block along the lower end of the gate fits. The watertight joint, however, is made by means of a seal on the under side of the block on the gate in the form of a rubber flap 1 inch thick, which is forced against the seat by the water pressure itself. The weight of the gates is decreased by water-tight compartments near the bottom, which give flotation. A trunk extends from the deck to these compartments. Some of the upper water-tight chambers may be filled so as to control the buoyancy of the gates for different levels of water. When in motion the gates hang simply on their hinges, and there are no rollers on the floor of the lock, the weight being carried principally by the buoyancy of the chambers.
CONSTRUCTING THE LOCKS
In deciding on the site for the locks, extensive and elaborate borings were made, indicating the exact character of the material. In every case a rock foundation was selected.
The Gatun locks were constructed somewhat earlier than those at Pedro Miguel and Miraflores, and the method of building them also differed from that used for the others. The conditions were not so favorable for economical work. The three Gatun locks and the approach walls contain over 2,000,000 cubic yards of concrete. For purpose of comparison it may be stated that a large modern dry dock contains less than one-tenth this amount.
The broken stone was obtained from quarries at Porto Bello, which were opened particularly for the lock work. The material was quarried and crushed at Porto Bello, and was transported on barges in tow of commission tugs and carried through the old French canal, which happened to pass very close to the site selected for the locks. On account of the silting in of the old canal and the long haul, the cost of transportation was quite materially increased. The cost of the stone delivered at Gatun, including cost of plant and overhead charges, averaged $2.40 per cubic yard. The sand was dredged at Nombre de Dios and similarly transported on barges, at a total cost of about $2.10 per cubic yard. Cement was shipped from the United States to Colon, transferred by train and placed in storehouses at Gatun. The mixing of the concrete was done at a stationary mixing plant. The stone, sand and cement were transferred by gravity, in proper proportions for each batch, to cars which dumped the materials into the mixers. After thorough mixing, the concrete was discharged into buckets on electric cars which ran on an automatically operated electric railroad. The cars were carried to tracks parallel to the locks and were stopped at the proper point. To transfer the concrete to the desired location in the lock, a number of aerial cableways were used, extending from one side to the other of the locks. The cable at one end was fastened to the top of a movable tower which contained hoisting apparatus, and at the other end the cable was fastened to a tower that was also movable but contained no machinery. The concrete was lifted from the cars, and by a trolley operating on the cableway was carried over the point of deposit, lowered and dumped.
The forms for the interior face of the side walls consisted of a heavy steel frame with steel face plates which were moved into position. The full height of the wall for the length of the form was then constructed, whereupon the form was moved to the next section. The cost of concrete on the Gatun locks was $6.64 per cubic yard in 1911 and $7.76 in 1912.
For the Miraflores locks broken stone was brought from a very large quarry opened high up on the side of Ancon Hill, where a satisfactory quality of stone was found. About 5,000 cubic yards of stone were turned out daily. Heavy blasts were set off above the berm, and steam shovels then loaded the material into railroad dump cars, which were switched farther down the hill by locomotives to the top of a crusher, and then dumped directly into it. “Dobe" shots were fired off in the cars to split the stones which were too large. The crusher could take stones equal in size to that of an ordinary chair. The crushed material was screened, and that of proper size was carried by a rubber belt to a sorting-screen and passed into the storage bins underneath for the various sizes. The material from the large crusher which was rejected by the screen passed into four small gyratory crushers, and from these on to the same belt for transfer to the sorting-screen. With this efficient and well-arranged plant the cost of stone delivered at the site of the locks was about $0.82 per cubic yard. The capacity of the Panama Railroad was insufficient to supply this material to the works at Gatun on the other side of the Isthmus.
Sand for the Miraflores locks was obtained by dredging at Chamé, transferred by barges to Balboa, where it was unloaded by means of grab buckets and placed in overhead storage bins for transfer by rail to the lock site. The total cost in storage at the locks was about $0.76 per cubic yard.
To handle the stone and sand in building the Miraflores locks, an elevated trestle was built parallel to the locks and about 200 feet away. The cars dumped the stone on the side toward the locks, and the sand on the side away from them. On the bank between the locks and the storage pile a large cantilever crane operated on a track. The tower contained bins and