The Panama Canal Part 6

[14] This is the figure of official recruiting. Very many more came to the isthmus of their own accord.

CHAPTER XI.

THE PROBLEM OF CONSTRUCTION.

We may now begin to consider the ca.n.a.l itself, the problems which its designers had to solve, the methods of construction, and the features of the completed work. As we have seen, the first two and a half years were a time mainly of preparation for the t.i.tanic enterprise of excavation and construction. In fact, it might have been better if the work during that period had been entirely restricted to scavenging, sewering, and so forth. The labourers were hurried a little too fast to the isthmus, before the isthmus was properly cleaned up to receive them. Hence the yellow fever panic and difficulties which might have been avoided. The people of the United States were responsible for this over-haste at the start. The great thing, they cried, is to "make the dirt fly." They wanted evidence that the steam-navvies were actually at work in the bed of the ca.n.a.l and that the task was well in hand. In fact, the public at home took an interest in the ca.n.a.l operations which was sometimes embarra.s.sing. Some newspaper man at the isthmus would report an accident or unforeseen difficulty, probably with a good deal of exaggeration, an anxious excitement sprang up among the people, and special commissions had to go to the isthmus in order to investigate the true state of affairs and if possible restore confidence at home.

As the reader knows, the Americans had no clean slate on which to write at Panama. They succeeded two French companies which had been at work for twenty years. True, the New Panama Ca.n.a.l Company which succeeded the Lesseps Company had not greatly perspired over the undertaking. It had kept a certain amount of work going, chiefly in order to maintain its concession. All the same, the French had ploughed a pretty deep furrow between Colon and Panama, and much of the work they had done was fortunately available whichever type of ca.n.a.l should be adopted, high-level or tide-level. They had carried out a good deal of dredging for the channel through the tidal flats at either end of the ca.n.a.l, and they had made a very visible impression on the "continental divide" at what is known as the Culebra Cut. Altogether the French companies excavated 81,548,000 cubic yards. The Americans inherited from their predecessors a large amount of machinery and tools, in addition to a great deal of work well done. Much of the machinery, even of the Lesseps Company, was found to be in serviceable condition, and operations could be continued with it, though the extent and efficiency of the plant was, of course, as time went on, greatly increased.

The main problem which the American engineers had to solve was how to deal with the Chagres River. On the tide-level scheme, that violent and capricious stream, which in the rainy season was navigable for half its length of 100 miles, would have had to be diverted into another channel or ponded back in its upper waters by a high dam at Gamboa, some of the overflow of which might perhaps have been permitted to pa.s.s into the ca.n.a.l. But, as we have seen, the Chagres would have to be utilized and at the same time controlled if the high-level plan was adopted. A river which is capable of rising 35- feet in twenty-four hours needed a great deal of regulation and discipline before it could be used as the feeder of the upper reaches of a lock ca.n.a.l. The only way to do this was to diffuse its waters over a vast artificial lake which it would keep full, but in which its floods and current would be effectually tamed.

This could only be done by a huge dam intercepting the course of the river in its lower reaches, at some point before it entered the Caribbean Sea. When the New Panama Ca.n.a.l Company changed its plans and decided for an elevated waterway, it was intended to construct such a barrier at Bohio, a point much higher up stream than Gatun, the site ultimately chosen by the American engineers. The Isthmian Ca.n.a.l Commission which reported in 1901, also arranged for a dam at Bohio to control the Chagres River. On this plan the river would have been intercepted much higher up, and the artificial lake would have been much smaller. But when the Americans finally decided on the high-level type in 1906, the site of the proposed dam was shifted from Bohio to Gatun, nearer the river's mouth, which involved the inundation of a much vaster area of country. This position for the dam was first suggested by a French engineer, G.o.din de Lepinay, who, in a paper read before the congress of engineers in Paris in 1879, advocated a lock ca.n.a.l with a dam controlling the Chagres River at Gatun. This, then, was the biggest problem peculiar to the high-level scheme, for the cutting through the "continental divide," though an even more t.i.tanic labour, would have had to be accomplished whatever type of ca.n.a.l had been adopted.

No feature of the construction has been subject to so much criticism and anxious solicitude as this Gatun d.y.k.e. On it depends the maintenance of Gatun Lake and the supply of water for the ca.n.a.l. If the dam fails, everything fails. The real cause of the difficulty was the foundation upon which this big artificial hill had to be laid. The great dam at a.s.souan in Egypt is based upon the eternal granite, upon which masonry of natural stone is built. It is, therefore, part and parcel of the solid framework of our planet, and will probably last as long. The Gatun dam is, however, founded upon the alluvial deposits of the Chagres River. This alluvium consists of gravel firmly cemented with mud and clay, and is unquestionably water-tight. These deposits go down in places to a depth of 280 feet before the solid rock is reached. The dam had, therefore, to be laid down on the top of them.

Now this foundation, though water-tight, is soft. It would have been impossible to place upon it a ma.s.sive structure of rock or concrete. The deposits would have given way under its weight. The only plan was to dump down in the valley an earthen dam, making it very broad so as to distribute the weight over as large a s.p.a.ce as possible of the alluvium underneath. A steep slope would have been impossible, for the weight of the central portion would have pushed the clay and gravel outwards, and the whole ma.s.s would have subsided. The earth-dam was to block the valley through which the Chagres had hitherto flowed uninterruptedly to the sea. This valley is a mile and a half wide, and this is, therefore, the length of the dam. Its base is 2,100 feet wide. It is 398 feet through at the surface of the water, 100 feet wide at the top, and was to be 115 feet above sea-level. The last figure has, it seems, been brought down to 104 feet, which will be an advantage, as the weight upon the foundations will be proportionately less.

In the middle of the dam the level of the lake is controlled by a channel called the "spillway," with walls and floor of concrete, by which the surplus waters will be sluiced off into the old bed of the Chagres River and so pa.s.sed on to the sea. The entrance to this channel is closed with falling gates or doors. This safety-valve will no doubt be capable of dealing with the biggest and quickest rise of the lake-level that is ever likely to take place. It can pa.s.s off 137,000 cubic feet of water a second, the water issuing at a speed of 35 feet a second. But, to complete the security, the big culverts of the mighty Gatun locks close by can be turned open, and 170,000 cubic feet a second carried off there. Indeed, as regards the Gatun Lake the anxiety, if there be any, is that the water-supply will be insufficient rather than dangerously excessive.

The level of the lake is to be kept at 85 feet above mean sea-level--that is, the dam, or a considerable length of it, will be exposed to what is called a "head" of water of 85 feet. The lake itself will be 164 square miles in extent. There have been many rational anxieties on the sufficiency of the dam. A certain American senator, however, who visited the works during the construction, worried himself rather unnecessarily on this last figure. Colonel Goethals was showing a congressional delegation round the works, and in the course of the survey they came to the dam with the broad expanse of water behind it.

"Colonel," he said, "how is it that so small a body of earth as the Gatun dam can hold in check such a tremendous body of water as the Gatun Lake?" The chief engineer explained that the pressure of a body of water is determined by its height and not by its volume. The inquirer seems not to have been satisfied with the statement of this hydrostatic law.

Senator Knox, afterwards Secretary of State, then came to his aid.

"Senator," he said, "if your theory were true, how could the d.y.k.es of Holland hold in check the Atlantic Ocean?" This was a clincher, and the sceptic joined in the laugh at his own expense.

All the same, the Gatun dam has two extremely responsible and heavy duties to perform. It has to withstand the horizontal thrust of a head of 85 feet of water so as not to be carried bodily down the Chagres bed into the Atlantic. And it has to block up the valley so effectually that the water of the lake shall not percolate through at any point. There is every reason to believe that, in spite of all alarums and excursions during its construction, it will fulfil both these requirements. Its composition and construction may be briefly described. Two bulwarks of big rocky fragments were built up on either outer line or "toe" of the structure. This rough material was obtained from the lock site, or Mindi, or the Culebra Cut twenty-six miles away. The area between these piles is filled with silt, and water pumped into it by hydraulic dredges from the Chagres valley. The surplus water is carried off through pipes.

The sodden silt remains and is packed down and consolidated by atmospheric pressure. Such a "hydraulic fill" is impervious to water, the thrust or "head" of which is very quickly lost in the minute interstices or pores of the material. It will be seen how such a structure differs from a dam of concrete or stone masonry. It is porous, while at the same time impervious to water.

The future traveller through the Panama Ca.n.a.l will probably never guess the immensity of the labour that has gone to the building of the Gatun dam. Already, indeed, it looks so much like a part of the natural landscape that it might well escape special observation altogether. Yet nothing less than 21,145,931 cubic yards of material were laid down--enough to make a wall of earth three feet high and three feet thick reaching nearly halfway round the world. The spillway itself contains 225,485 cubic yards of concrete.

It will be noticed that in the dam proper there is no core of masonry or puddled chalk or clay whatever. It was at one time intended that there should be. I have alluded to the alarmist rumours that were raised again and again at Panama and created much uneasiness in the United States.

These were especially concerned with the great dam, and that word must have frequently been on the lips of the engineers in more than one significance. Every possible test was applied to determine the exact character of the underlying materials, to ascertain whether there was any connection between the swamp areas to the north and south through the deposits in the gorges which the earthwork was to bridge, to prove the ability of the material below to support the structure, and to find out whether suitable material for the dam could be found in its neighbourhood. "As the result of all these investigations," wrote Colonel Goethals,[15] "it may be briefly stated that the underlying material is impervious to water; that it possesses ample strength to uphold the structure that will be placed upon it, and, the subsoil being impervious, that there is no connection between the swamps above and the sea below."

In order to make a.s.surance doubly sure, Colonel Goethals planned the dam so as to include triple interlocking steel sheet-piling across the valley, driven down to bedrock, and decided to carry the dam to a height of 135 feet. Even so, the news of a collapse was wired home, and this so impressed President Roosevelt that he sent a commission of engineers to the isthmus accompanied by President-elect Taft. The investigations had a different result from what had been expected. Instead of being dissatisfied with the size and strength of the dam, the engineers declared that it was being built too high and that the steel piling was unnecessary. It must be admitted, therefore, that the efficiency of the Gatun dam has been subjected to the most rigorous tests, and that no further anxiety on the subject need be felt.

With the blocking of the Chagres outlet at Gatun, the waters of the lake have gradually acc.u.mulated until they cover an area of 164 square miles.

Not only the Chagres itself but its tributaries, the Trinidad and others, are thus ponded back. The reservoir extends up a number of long and winding arms, and is thus very irregular in shape. The bed of the channel itself was cleared of brushwood and trees, but the rest of the valley was thickly overgrown. As the waters rose, therefore, and gradually submerged this primeval forest, a rather dismal spectacle was presented of decay and destruction. The lake has, indeed, completely altered the aspect of the country. Villages and even small towns, whose names had come down from the days of the old navigators, lie buried for ever beneath the waters of Lake Gatun. Even now the great expanse of water with its wooded islands looks like a natural feature of the landscape rather than yesterday's creation of engineering enterprise.

The vessels in transit will, of course, keep to the dredged and buoyed channel, but the channel will itself be invisible, and the traveller, after tossing on the restless Caribbean Sea, will enjoy the full sensation of a cruise over a landlocked fjord or lake. Lake Gatun is indeed twice the size of Lago Maggiore and four-fifths the size of Lake Geneva. The journey from Gatun to Bas Obispo, where the waterway again a.s.sumes the appearance of a ca.n.a.l and enters the Culebra gorge, is 22 miles, but the same 85-foot level is maintained right to the locks at Pedro Miguel, where the waters of Lake Gatun are again retained by a dam connecting the walls of the lock with a hill to the west. The rest of the lake is held in by the natural configuration of the country, the only outlets being at the Gatun spillway and, of course, through the locks.

But we must not overlook the main purpose of the lake, which is to supply the water for the ca.n.a.l and the lockages. For this purpose everything, of course, depends on the rainfall at the isthmus, and the question arises whether this may be relied upon to replenish the ca.n.a.l with the needful water-supply. Colonel Goethals estimates that in an average dry season 58 "lockages," or transits of the ca.n.a.l, per day would be possible, which is a greater number than the twenty-four hours of the day would permit, allowing vessels to follow each other at intervals of one hour. Happily, a resource is still left if the supply of water should show signs of proving insufficient. At Alhajuela, on the Chagres River, some nine or ten miles above Obispo, there is an excellent site for a dam, forming a reservoir where some of the surplus water of the rainy season could be stored and supplied to the ca.n.a.l as required in the dry months. Details of the construction of such a dam were prepared in connection with a former ca.n.a.l-scheme, and would be available in case of need.

FOOTNOTES:

[15] _The National Geographic Magazine_, February 1911.

CHAPTER XII.

THE CULEBRA CUT.

The most famous section of work on the ca.n.a.l has been that at the vertebra or "continental divide," which runs along the isthmus on the Pacific side and had to be pierced through by any ca.n.a.l running from Colon to Panama. This tremendous work, known as the "Culebra Cut," from the name of one of the hills, extends for nine miles from Bas Obispo to Pedro Miguel. Mr. Bryce has truly said, referring to this section, that "never before on our planet have so much labour, so much scientific knowledge, and so much executive skill been concentrated on a work designed to bring the nations nearer to one another and serve the interests of all mankind."[16] The bottom of the ca.n.a.l in the cut, as in the channel through Lake Gatun, is 40 feet above sea-level. The highest elevation of the original surface of the ground above the centre line of the ca.n.a.l was 312 feet above sea-level, so that the total excavation along this saddle was 312 minus 40, or 272 feet. This was, however, not actually the highest point of excavation. Gold Hill, close to the ca.n.a.l line, is 534 feet above sea-level, and from the top of this hill a new and steeper slope had to be made. The surface of the water is 85 feet above sea-level, and so is 227 feet below the original saddle at its highest elevation. We have already noticed that a tide-level ca.n.a.l would have involved an excavation 85 feet deeper, and the width of the cutting would have had to be immensely wider. The slides and breaks which have rendered the American excavation so much more difficult lead one to suppose that the tide-level cutting might have proved impracticable.

All the work at Culebra performed by the French was available for their successors. The French companies accounted for 18,646,000 cubic yards of material on this section. They had already cut down 152 feet below the original surface at its highest elevation, and the cliff they had cut in the face of Gold Hill was 374 feet in vertical height. It is well to mention such figures, as some people imagine that the French wasted all their time and resources at Panama. It may be added that the bottom width of the channel adopted by the French engineers was 74 feet, whereas that of the American ca.n.a.l will be 300 feet.

Many descriptions have been given by visitors of the spectacle presented in this long and deep gash through the mountains during the progress of the excavations. From these and the numerous photographs taken at that stage the traveller will be able to reconstruct the scene--the two hundred miles of railroad construction track, laid down tier above tier at different levels; the thousands of men busily at work; the roar and smoke of the dynamite tearing the rock into fragments; the mighty steam-shovels like great dragons burying their iron teeth in the surface of the bank, engulfing a huge mouthful, then swinging round and belching it all into the dirt trucks, to be carried off to the dumping-ground at Gatun near the Atlantic or Balboa at the Pacific end of the ca.n.a.l. At Culebra, Colonel Goethals made the "dirt fly" to the full satisfaction of public opinion in the United States. All sorts of devices and machinery were employed to hasten and economize the process. For example, there was the Ledgerwood Unloader. Railway trucks provided with flaps were used, these flaps making a single platform of the whole train. At the rear of the train was a plough which could be drawn by a wire rope attached to a drum carried on a special car in the fore part of the train. When the train arrived at the dumping-ground the drum was started, and the plough, advancing from the rear, swept the 320 cubic yards and rock from the sixteen cars in seven minutes. Then there was a "track-shifter," invented by an employee on the isthmus, which lifted and relaid the railway lines as the spoil-tracks had to be shifted. This powerful engine raised the track and ties clear of the ground and deposited them from three to nine feet sideways.

The "spoil trains" were treated with all the respect which is accorded to the fastest mail trains of the day on an English main line. They followed one another from the cutting at intervals of three minutes, and any delay, of course, balked the mammoth steam-shovel of its gluttonous meal on the stones and rubble of the mountain-side. Any cause of delay was at once reported by telephone to the superintendent of transportation at Empire, and the obstruction was immediately dealt with. By this persistent concentration on the main object the dirt has been made to fly not only more speedily but more cheaply.

One of the most serious causes of anxiety and difficulty along the ca.n.a.l line were the "slides" and "breaks" which kept occurring in the Culebra Cut. To use a condensed Americanism, the sides would not "stay put."

Large ma.s.ses of material would slide or move from the banks into the excavated area, closing off the drainage, upsetting the steam-shovels, and tearing up the tracks. A very unpleasant phenomenon was the lifting of the shovels in the bottom of the ca.n.a.l due to the bulgings of the earth there. It is not necessary to enter into the distinction between "slides" and "breaks," or into the learned disquisitions that have been written about them. It is sufficient for us to note that they added immensely to the amount of material which had to be got out of the Culebra gorge. Colonel Goethals tells us that of the 14,325,876 cubic yards removed during the year 1909, 884,530 cubic yards, or 6 per cent., were due to slides; that in 1910 of 14,921,750 cubic yards removed, 2,649,000, or 18 per cent., came from slides or breaks that had previously existed or that had developed during the year.

It might have been imagined that these discouraging additions to the work would have seriously delayed progress on the ca.n.a.l and put forward the date of its completion. But able and economic organization triumphed over all these lets and hindrances. At the beginning of the American excavations the engineers estimated that 103 million cubic yards of "dirt" had still to be removed, and that this work would take nine years to accomplish. But that estimate of material proved to be greatly below the mark. Enlargements of the ca.n.a.l and the unforeseen collapses in the Culebra Cut brought up the total to 195 million cubic yards. It is a remarkable evidence of the efficiency and economy of the American organization that this immense task will have been completed in about six years of actual full-swing work.

Some idea of the way in which Colonel Goethals made the dirt fly may be gathered from the fact that in the first five years of his directorship, down to April 1912, he removed 160 million cubic yards of material. "If all this material," writes Mr. Showalter, "could be placed in a solid shaft of the shape of the Washington Monument, with a base as large as an average city block, it would tower more than six miles skyward, overtopping the earth's loftiest mountain peak by more than a mile.

Again, if it were to be loaded on to the big Lidgerwood dirt cars used on the ca.n.a.l, it would make a string of them reaching over two and a half times around the earth, and requiring a string of engines reaching from New York to Sac Francisco to move them." It is indeed a remarkable achievement that, while the amount of material to be removed was increased by about 90 per cent., the time of removal was cut down by 30 per cent. Nor has the increase of the work added to the estimate of cost. The total cost of the completed ca.n.a.l was fixed in 1908 at 375 million dollars. Yet, in spite of the increased excavations, enough of this sum, it is calculated, will be left over to build a new breakwater, and perhaps a big storage reservoir at Alhajuela on the upper reaches of the Chagres River. In the Culebra Cut, despite the landslides, the cost of excavation has actually been reduced by more than one-third.

[Ill.u.s.tration: Culebra Cut, from West Bank, showing Shovels at Work.]

The pessimists have of course been busy with these landslides in the "Cut." They predicted that the ca.n.a.l along this section would always be exposed to danger from that source. But here, too, every precaution has been taken. The engineers have given a much lower slope to the sides of the ca.n.a.l, which is therefore wider at the top than had been originally planned. The slopes will also be sown with creeping gra.s.ses and other plants, which will bind down the surface soil. When the forty-five feet of water are in the ca.n.a.l, the bottom will be held down by the weight, and the bulgings no longer take place. Moreover, any earth that, in spite of all precautions, still manages to slide into the ca.n.a.l should be easily dealt with by the big 20-inch suction dredges, which can be brought up through the locks and set to work. So we need not trouble much about the stability of things along this nine-mile section through the Culebra Mountains.

Here as elsewhere it is possible to give only a very general idea of the difficulties which were encountered and overcome in the course of construction. The drainage of the "Cut" during the work was in itself a heavy and important task. It was necessary to keep out the water of the surrounding country and to rid the excavated area of water collecting in it. A system of diversion channels, carrying off the Obispo River and its tributaries, effected the first object, and the second problem was solved by gravity drains and pumps. On the whole, this mighty trench through the isthmian hills is not only the biggest thing to the credit of a nation which delights in bigness, but the greatest achievement of its kind the world has ever seen.

FOOTNOTES:

[16] "South America," p. 26.

CHAPTER XIII.

THE LOCKS.

The Panama Ca.n.a.l belongs to the "age of concrete." All other vast works of construction, such as the Pyramids of antiquity and the a.s.souan Dam of to-day, have been built of live natural rock. At Panama everything--locks, wharves, piers, breakwaters--has been constructed of concrete. The Americans have not only built these incomparable piles of masonry; they have manufactured the material out of which they are built. This circ.u.mstance makes the rapid completion of the ca.n.a.l all the more wonderful. Not less than four and a half million cubic yards of artificial stone have been produced for the built portions of the ca.n.a.l and its accessories. This amount of concrete, we are informed, would make an ordinary sidewalk nine feet wide by six inches thick reaching more than twice round the earth.

The broken stone which is one of the ingredients of concrete was quarried and transported from Porto Bello--a name famous in the annals of West Indian romance--20 miles to the east of Colon; while the sand came mostly from Nombre de Dios, also a celebrated place 20 miles further to the east, the Atlantic terminal of the old paved trans-isthmian road along which the Spanish mule convoys brought the silver of the Incas from Panama. Millions of yards of stone came from Porto Bello. Hundreds of bargeloads of sand came from Nombre de Dios and from islands in the Atlantic and Pacific. Myriads of barrels of cement were shipped from the United States to Cristobal, an outskirt of Colon, thence carried by barges to Gatun or by railway to the Pedro Miguel and Miraflores lock sites. Dozens of mighty "mixers" were ready to receive these diverse materials. Each of these could accommodate ten tons of sand, cement, crushed stones, and water. This indigestible mixture the machine would toss and churn round for a minute or so in its interior and then belch it all out in the shape of unhardened artificial stone.

The belief in concrete among the builders of the Panama Ca.n.a.l has been almost a superst.i.tion. They invented a sort of cement gun to shoot sand and water against the sides of the Culebra Cut, so as to form a coating of solid artificial rock, but the experiment rather deserved than achieved success. Of course all such structures as lighthouses were built wholly of concrete, and it is reported that even barges were constructed of this adaptable material. As regards concrete and its nature and behaviour nothing was taken for granted. Every means was taken of testing such important matters as the effect of sea-water on this material, the time it takes for these huge ma.s.ses of artificial stone to settle, and many other questions on the answer to which the permanence and stability of the locks and the entire waterway would depend. The Panama Ca.n.a.l, writes Mr. Showalter, is "the greatest effort man ever has made, and perhaps ever will make, to simulate the processes of geologic ages, and do in days what Nature required unreckoned years to accomplish."

These remarks about concrete naturally lead us to the subject of the Panama locks, the magnificent stairway at Gatun, the single-step locks at Pedro Miguel (or, as the worker quickly Anglicized it, Peter Magill), and the double-step flight at Miraflores. The most impressive of these is the colossal duplicated three-step flight at Gatun, up which the vessel in transit is lifted from the end of the sea-level seven-mile-long entrance channel through Limon Bay to Gatun up to the surface of Gatun Lake, 85 feet above the level of the sea. This giant staircase has been constructed in a cutting through the hill which retains at this end the waters of the artificial lake. A tremendous amount of excavation, upwards of 5,000,000 cubic yards, was necessary, and the locks, which are constructed entirely of concrete, contain about 2,046,100 cubic yards of that material. The chambers of all the locks in the ca.n.a.l will have a usable length of 1,000 feet and a width of 110 feet. These dimensions should prove large enough for the largest ships not only existing but likely to be constructed for many years to come.

They satisfy the requirement of the Spooner Act that the ca.n.a.l shall be "of sufficient capacity and depth to afford convenient pa.s.sage for vessels of the largest tonnage and greatest draft now in use, and such as may reasonably be expected." More than 95 per cent. of the ships now afloat are less than 600 feet in length, so that a good margin is allowed. We may be certain that the American government has given the closest attention to the question of the length and breadth of the lock-chambers, for the ca.n.a.l, we must remember, is primarily a military pa.s.sage for the purpose of transferring, if need be, the entire American fleet from the Atlantic to the Pacific seaboard. The locks of the Kiel Ca.n.a.l, it may be added for purposes of comparison, have an available length of 492 feet and a width of 82 feet.

The vessel, then, in order to gain the level of Gatun Lake from the Atlantic entrance, has to pa.s.s through a flight of three successive locks. The maximum lift is 32 feet, or about four feet higher than at any other locks now in use. All the locks along the Panama Ca.n.a.l are duplicated--that is, there are two parallel sets with a common centre-wall--so that two ships could be simultaneously put through both flights in the same or in opposite directions. This "double-tracking"