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cost of the canal. So far as commercial needs are concerned the present provisions are extremely liberal. So far as naval needs are concerned no one can foretell what results the rapid and radical developments of the present decade may disclose.

THE SEA-LEVEL SECTIONS AND THE TERMINALS

Limon Bay, through which the Atlantic sea-level section passes, faces directly north and is open to the northerly storms and seas, which are quite severe at certain times. Protection was necessary in order: first, that ships might enter the canal in quiet water; second, to provide a quiet anchorage; third, to make traffic in small boats feasible and safe between the shore and ships at anchor; fourth, to prevent the movement of silts and sands by the seas and the attendant dredging expenditure. (See plan No. 2.)

To give this protection, Toro Point breakwater has been constructed, extending from Toro Point in a northeasterly direction for a distance of about 2 miles. The outer end does not quite cover the entrance to the canal. The breakwater protects the greater part of Limon Bay from the northerly storms, but the easterly portion is still exposed, especially to waves and trade winds from a northeasterly direction. The construction of a breakwater to close this part of the bay was postponed to await the results of actual experience with the one at Toro Point. It seemed probable at the time that this breakwater would ultimately be built, as the protection was not sufficient, especially for boating, and as the effects of wave action cause silting of the channel. It was actually found as a result of the experience of the navy that it would be dangerous and at times impossible for small boats and coal barges to lie alongside ships. Furthermore, an estimate showed that 2,200,000 cubic yards of material, costing several hundred thousand dollars to remove, had been deposited in the finished channel during twelve months' action of the waves. The construction of the east breakwater was accordingly decided upon.

The Toro Point breakwater was constructed from a trestle supported on creosoted piles 85 feet long and having two tracks. The piles were driven by a railroad pile-driver with very heavy hammer, which could reach all of the piles from either track. Stone from a Toro Point quarry was carried in cars on the trestle and dumped overboard, and forms the core of the breakwater. Porto Bello stone, which is harder and much more durable, was transported a distance of about 28 miles on barges and carefully deposited on the exterior by means of derricks. The breakwater is 20 feet in width on top, and is built in water from 35 to 50 feet in depth. The height of the top above the surface of the water is about 16 feet. The total quantity of material placed to December 31, 1912, when the breakwater was nearly completed, was 954,500 cubic yards, at an average cost of $2.20 per cubic yard. In addition, 620,000 cubic yards of rock dredged from the canal were deposited in the vicinity of the breakwater. During the fiscal year 1912 the Toro Point rock cost $1.38 per cubic yard, and the Porto Bello rock, $4.31.

A large anchorage basin is provided between Cristobal and the canal channel. The wharfage space at Cristobal is being increased. New piers are built on steel cylinders which were excavated inside by hand and gradually forced down.

The cylinders, upon reaching the proper depth, were filled with concrete, and a superstructure of reinforced concrete was built

upon them.

To complete the Atlantic sea-level section, from the outer end to its terminus at the Gatun Locks, required the excavation of over 32,000,000 cubic yards by dredging, costing over $7,600,000, or about 24 cents per cubic yard; and over 2,000,000 cubic yards by steam shovel, costing over $1,450,000, or about 67 cents per cubic yard.

The Pacific sea-level section from the Miraflores Locks to Panama Bay cuts the winding channel of the Rio Grande River and then continues through the bay. The land is all very low. This channel up to December 31, 1912, when the work was well in hand, had required the excavation of over 34,500,000 cubic yards by dredging, at a total cost of over $8,500,000, or about 25 cents per cubic yard; over 2,500,000 cubic yards by steam shovel, at a cost of over $2,000,000, or about 80 cents per cubic yard, and in addition over 1,500,000 cubic yards by hydraulic excavation, at a total cost of over $1,100,000, or about 72 cents per cubic yard. The hydraulic excavation consisted in dislodging the earth by means of powerful streams of water and carrying the material, water-borne, to suction pumps which discharged it on the neighboring

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Fig. 17. — Emergency Dam at Pedro Miguel Locks under test with lock empty. The bridge has
been turned like a drawbridge until it spans the lock. Vertical girders are being lowered and will rest
against concrete shelf on floor of lock. Then the checkered plates will be slid down on the vertical
girders thus forming a steel wall. This operation may be performed with water flowing through the
lock in case of damage to a gate.

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