利用者:Hrs885/作業場1

The Gaillard Cut, or Culebra Cut, is a man-made valley that cuts through the continental divide in Panama. The cut forms part of the Panama Canal, linking Lake Gatún, and thereby the Atlantic Ocean, to the Gulf of Panama and the Pacific Ocean. It is 12.6 km (7.8 miles) from the Pedro Miguel lock on the Pacific side to the Chagres River arm of Lake Gatun, with a water level 26 m (85 ft) above sea level.

Construction of the cut was one of the great engineering feats of its time; the immense effort required to complete it was justified by the great significance of the canal to shipping, and in particular the strategic interests of the United States.

Construction[編集]

The French[編集]

As described in History of the Panama Canal, the excavation of the Culebra Cut was begun by a French venture, led by Ferdinand de Lesseps, which was attempting to build a sea-level canal between the oceans, with a bottom width of 22 metres (72 ft). Digging at Culebra began on January 22, 1882. A combination of disease, underestimation of the problem, and financial difficulties led to the collapse of the French effort, which was bought out by the United States in 1904. The French had excavated some 14,256,000 m³ (18,646,000 cubic yards) of material from the cut,^[1] and had lowered the summit from 64 metres (210 ft) above sea level^[2] to 59 metres (193 ft),^[3] over a relatively narrow width.

The United States[編集]

The United States took over on May 4, 1904. Under the leadership of John Stevens, and later George Washington Goethals, the American effort started work on a wider, but less deep cut, as part of a new plan for an elevated lock-based canal, with a bottom width of 91 metres (300 ft); this would require creation of a valley up to 540 metres (a third of a mile) wide at the top. Vast amounts of new equipment were imported, and a comprehensive system of railways was constructed for the removal of the immense amounts of spoil.

Major David du Bose Gaillard, of the U.S. Army Corps of Engineers, joined the project at the same time as Goethals, and was put in charge of the central district of the canal, which was responsible for everything between Gatun and the Pedro Miguel locks — most notably, the Culebra Cut. Gaillard brought dedication and quiet, clear-sighted leadership to his difficult, complex task.

The scale of the work was massive. Hundreds of drills prepared holes in which were planted tons of dynamite, which blasted the rock of the cut so that it could be excavated by steam shovels. Dozens of dirt trains took the spoil from the shovels to the dumps, some twelve miles (19 km) distant. In a typical day, 160 trainloads of material were hauled away from a cut nine miles (14 km) long. This required skillful co-ordination; at the busiest times, there was a train in or out almost every minute.

Six thousand men worked in the cut, drilling, placing explosives, handling shovels and the dirt trains, and shifting the tracks as the work moved forward. Twice a day work stopped for blasting, and then the shovels moved in to take the loose dirt away. More than 600 holes were fired daily; in all, 60 million pounds (27,000 tonnes) of dynamite were used. At times, 52,000 pounds (23,600 kg) of dynamite were used in a single blast.

Landslides[編集]

The excavation of the cut was one of the greatest areas of uncertainty in the creation of the canal, due to the unpredicted large landslides. The International Board of Consulting Engineers had mistakenly decided that the rock would be stable at a height of 73.5 metres with a slope of 1 in 1.5; in practice, the rock began to collapse from that slope at a height of only 19.5 metres. The misjudgment was in part due to unforeseen oxidation of the underlying iron strata due to water infiltration, which caused weakening and eventually a collapse of the strata.

The first and largest major slide occurred in 1907 at Cucaracha. The initial crack was first noted on October 4th, 1907, followed by the mass wasting of about 382,000 m³ (500,000 cubic yards) of clay. This slide caused many people to suggest the construction of the Panama Canal would be impossible; Gaillard described the slides as tropical glaciers, made of mud instead of ice. The clay was too soft to be excavated by the steam shovels and was eventually removed by sluicing with water from a high level.

After this, the sediment in the upper levels of the cut was removed, resulting in less weight over the weak strata. The slide still continued to cause minor problems after this.

Completion[編集]

Steam shovels broke through the Culebra Cut in May, 1913. The Americans had lowered the summit of the cut from 59 metres (193 ft) to 12 metres (40 ft) above sea level, at the same time widening it considerably, and had excavated over 76 million cubic metres m³ (100 million cubic yards) of material. Some 23,000,000 m³ (30,000,000 cubic yards) of this material was additional to the planned excavation, having been brought into the cut by the landslides.

Gaillard died from a brain tumour in Baltimore, on December 5, 1913, having been promoted to colonel a month before, and hence never saw the opening of the canal in 1914. The Culebra Cut, as it was originally known, was renamed to the Gaillard Cut on April 27, 1915, in his honour.^[4]

References[編集]

^ The French Failure, from CZBrats
^ The Canal Zone / Profile of the Canal, from the Perry-Castañeda Library Map Collection
^ How The Shovels Work, from The Panama Canal, by Colonel George W. Goethals
^ Cut Named For Construction Day Engineer, by Joaquin Horna

Making the Dirt Fly, Building the Panama Canal Smithsonian Institution Libraries