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to the proper shovel; there were loaded trains to be moved on, and loaded trains to be passed out of the cut; there were workmen's trains, accident cases, special locomotives, and other traffic to handle. There was scarcely a moment when some definite action, affecting the economy of the entire operation, was not expected of the train dispatcher. The trains were passed on to the construction tracks and thence to the main line of the Panama Railroad. The dirt trains invariably had the right-of-way. To observe the work of these train dispatchers, and to see the constant procession of dirt trains and empties rolling along the main line of the Panama Railroad, was most impressive. The traffic was probably equal to that on the main lines of the important trunk lines of the United States. The amount of traffic is indicated by considering the average number of locomotives and cars in use during a typical year, namely 1912, as shown by the following table:

Average Daily LOCOMOTIVES AND CARS

Number in

Use, 1912 Locomotives handling spreaders.

6 Locomotives handling unloaders..

10 Locomotives handling track shifters ..

3 Locomotives handling dirt and miscellaneous trains... 117 Lidgerwood flat cars, average per day.

2403 Large steel dump cars

320 Small steel dump cars.

973

The largest number of cars handled in one day during the year 1912 was 4896. In other years the total was even larger. The number of shovels in use during this year was 46, of which nearly half were 95-ton shovels with a dipper capacity of 5 cubic yards. The highest daily yardage for one shovel was 4465 cubic yards. The highest annual record was 543,481 cubic yards. The average amount of material handled per shovel per hour increased from 121 cubic yards in 1908 to 165 cubic yards in 1912. In the meantime the average cost per cubic yard of excavation dropped from $0.725 in 1908 to $0.55 in 1912.

The disposal of the excavated material required most careful thought and involved considerable engineering ability. The rate of progress on the Culebra Cut, and, therefore, the rate of progress on the whole canal, at various times depended upon the speed at which the trains could dispose of their loads of dirt. Where the material could possibly be of any use, trestles were built and the material was deposited without rehandling directly where it was needed, as in the Gatun Dam, the back fill behind the lock walls, the embankments of the new Panama Railroad, and in raising the level of swamp lands, making land, and building a breakwater at the Pacific entrance of the canal. The vast bulk of the material was wasted. The principal dumps were at Tabernilla, Gatun, Miraflores, Balboa and the Panama Railroad relocation. Each of these dumps took from 5,000,000 to 18,000,000 cubic yards. Trestles were first built to dump material off the cars; and as the level of this fill rose, the track was removed from the trestle and shifted always toward the edge of the bank. It was the constant shifting of track and extension of trestles which caused the delays in disposal of material. The ingenious methods that had been developed on railroad work and elsewhere were utilized on the dumps. A small amount of the material was handled in steel sidedump cars which landed the material alongside the track. Air pressure from a locomotive was used in dumping these cars. Another and a more ingenious method for unloading them was by means of a large plow. The cars were flat and had a bulkhead on one side only; to balance this the other side overhung slightly more. When a train arrived at the dump an enormous plow of the full width of the car was set on one end of the train, and a cable led to the other end. The winding of the cable drew the plow the full length of the train and discharged all the material on the ground next to the track.

A further operation was necessary, because the track could not then be laid directly on the brink of the dump. The material which was piled up by the dumping of the cars was shoved off the edge of the embankment by means of an enormous plow, suspended over the area alongside the track from a special car, and pushed along by powerful locomotives. When the dump had been widened to a point where the plow or spreader could no longer slide the material out of the way, it was necessary to shift the track. Here again railroad experience was brought into play, and the work of hundreds of men was done by a small crew with a track shifter. This machine had two booms; the first lifted the track off the ground, the second was slewed, and a line passing over it was made fast to the track and drew the track into its new

70

The Panama Canal

location. The length of the booms was sufficient so that the weight of the shifter itself, which ran on the track, did not affect the work.

Special problems were encountered in some of the dumps, of which one of the most interesting was the disposition of silt and clays taken from the Chagres section of the Central Division. It became very soft when exposed during the rainy season, and the slop was found in some cases to be as flat as 1 vertical to 22 horizontal. It was impossible to maintain tracks on such material. Accordingly, a track was laid along the banks of the Chagres on hard ground, and when the material was dumped, it was thoroughly wetted by means of a 4-inch water pipe, whereupon the saturated material slid slowly but firmly into the Chagres River. The current was sufficient to carry it along and deposit it at points where it could do no harm.

In September 1913 steam shovel work in the Culebra Cut was completed, the decision having been reached to flood the cut and do the remaining digging by means of dredges. Controlling factors in this decision were: first, it was hoped that the weight of the water in the cut would have a deterrent effect on some of the slides and breaks; second, the remaining material required no drilling and blasting and could, therefore, be more economically handled by dredges; and third, the canal could be used for traffic while excavation was still in progress which would be impossible with shovels at work. The step forms a connecting link between canal construction and canal maintenance, since dredges will be continually at work to maintain the various channels. The French began excavating the Culebra Cut on January 20, 1882 and with the exception of the six 1889 to 1895 it has been in continuous progress covering a period of over 32 years.

years from

GEOLOGY AND THE SLIDES

The material through which the Culebra Cut passes is very variable. The region of the Isthmus was once geologically very active, and each period of activity is marked by material typical of the conditions under which it was formed. Fortunately, as in so many other parts of the world that were once the scene of geologic or volcanic activity, the Isthmus is now in a quiescent period and the great geologic forces are in a condition of comparatively stable equilibrium. When the canal project was being agitated there was great apprehension on the part of those not familiar with conditions as to possible volcanic eruptions or earthquakes. In allaying this feeling, the photographer of the flat arch in the ruins of the old Santo Domingo convent in Panama played a very important part. The fact that the arch has stood for so many years, while the roof and windows have disappeared and the masonry has deteriorated, adds to the impressiveness. Equally important, as proving the absence of seismic disturbances, is an almost exactly similar arch in a nearby church which still carries its superimposed floor load. Being in a different plane adds to the force of the evidence.

The comparatively infinitesimal forces controlled by the hand of man in a few localities produced minor

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