SLIDE ON WEST BANK OF THE CANAL NEAR CULEBRA
Picture shows about 1,000,000 cubic yards of material moving toward the cut at about three yards a day
To the unscientific mind the slides are terrifying in their magnitude and in the evidence they give of irresistible force. Man can no more check their advance than he can that of a glacier which in a way they resemble. When I was on the Isthmus the great Cucaracha slide was in progress, and had been for that matter since 1907. It had a total area of 47 acres and extended up the east bank of the Canal for about 1900 feet from the axis of the Canal. When it began its progress was disconcertingly rapid. Its base, foot, or “toe”—these anatomical terms in engineering are sometimes perplexing—moved across the canal bed at the rate of 14 feet a day. All that stood in its path was buried, torn to pieces or carried along with the resistless glacier of mud. Not content with filling the Canal from one side to the other, the dirt rose on the further side to a height of about 30 feet. Not only was the work of months obliterated, but work was laid out for years to come. Indeed in 1913 they were still digging at the Cucaracha slide and the end was not in sight. This slide was wholly a gravity slide, caused by a mass of earth slipping on the inclined surface of some smooth and slippery material like clay on which it rests. The nature of the phenomenon is clearly shown by the [diagram] printed on the next page in which the slide marked C is of the type just described.
ATTACKING THE CUCARACHA SLIDE
This slide has filled the Cut from side to side. A partial Cut has been dug through its center and the shovels are seen working on either side. The tracks are moved nightly as the material is removed.
On the west bank of the Canal occurred a slide of the second type caused by the crushing and squeezing out of underlying layers of soft material by the prodigious pressure of the high banks left untouched by the steam shovels. This slide is usually accompanied by the uprising of the bed of the Canal sometimes to a height of thirty feet. Col. Gaillard tells of standing on the bed of the Canal, observing the working of a steam shovel, when it gradually dawned upon him that he was no longer on the level of the shovel. At first he thought that the shovel must have been placed upon a bit of boggy land and was slowly sinking, but on investigation he discovered that the point on which he was standing had been slowly rising until within five minutes he had been lifted six feet without jar and with no sensation of motion. A perfectly simple illustration of the way in which this elevation of the bed of the Canal is caused may be obtained by pressing the hand upon a pan of dough. The dough will of course rise at the side of the hand. On the “big job” the towering hills furnished the pressure, the bed of the Canal rose like the dough. In the diagram already referred to, the slide to the right marked “B” is of the type here described. To cope with it, the work of the shovels and dirt trains in the Canal carrying the débris away is supplemented by others above removing the crest of the slide and thus lightening the pressure. In the [diagram] shovels are shown thus working on two levels, but I have seen four terraces of the same slide bearing steam shovels and rumbling dirt trains hurrying the débris away to where it will no longer be a menace.
DIAGRAM OF CULEBRA CUT SLIDES
C. is a slide moving over a slippery surface; the mass B breaks on a line of cleavage and crushes the underlying material, forcing it up at A. The steam shovels are working to reduce pressure on B
Courtesy of Scientific American