SLIDES AT THE PANAMA CANAL By Major General GEORGE W. GOETHALS, U. S. Army Governor of the Panama Canal Gift of the Panama CanalMmeum WASHINGTON GOVERNMENT PRINTING OFFICE 1916 rl-J- ■■>:--V- -s:^. -jfV.aT Jri-v'J SLIDES AT THE PANAMA CANAL. Extract from the Annual Report of Major General George W. Goethals, U. S. Army, Governor of the Panama Canal, for the fiscal year ended June 30, 1916. Although the question of the sUdes has been dealt with in pre- vious annual reports and official documents, there continues to exist much ignorance on the subject. Also a great deal has been written by those whose little knowledge makes them dangerous, and to whose statements credence is given because of the position or prom- inence of the writers. I have concluded, therefore, to report again on the situation, even at the expense of repetition, notwithstand- ing the general belief that anything pubhshed in annual reports is buried in obhvion. Consideration will be given also to the various theories that ^ave been advanced and to the remedies that have been suggested. For some unaccountable reason there seems to be a general belief that the entire length of the Cut is affected. A report emanating recently from English sources states that the bottom of the canal through this section is found to be a bog, which is being constantly pushed up, and through which the dredges have difficulty in main- taining a channel; further, that it is acknowledged on the part of those in charge that the canal is a failure, and that American engi- neers are seeking information in England relative to the Nicaragua route. Such reports are false, and there is no foundation for them; yet they seem to have gained credence probably because a pending treaty betw^een the United States and Nicaragua contemplates securing from the latter aU rights for building a canal on its territory. As the Nicaragua route was at one time the one most generally favored by the United States, investigations by commissions, boards, and commercial bodies, covering a series of years, have been made of the route, and data of aU kinds collected; consequently every- thing that is known about that route can be found at home, with- out the necessity of seeking information in England. It makes a good news item, however; makes converts to the belief that the 2 THE PANAMA CANAL. entire 8.75 miles of the Cut is unstable, liable to collapse or upheaval, completely closing the canal for all time, is useful in assisting ship- ping companies to take advantage of present conditions to charter ships at excessive rates instead of complying with their obligations, and permits an increase in insurance rates. Gaillard Cut extends from Pedro Miguel to Gamboa, a distance of 8.75 miles. The canal prism through this section averages 300 feet bottom width, and has a depth of 45 feet. Every foot of the exist- ing channel was excavated through rock, all of which, though of various kinds and densities, had to be drilled and blasted in order to remove it. It is possible that the water may have softened some of the material, yet it is known that the softer varieties of rock encountered in the excavation were protected from disintegration by contact with water. The bog theory is a myth. The Cut has been stable with the exceptions of the portions in the vicinity of Culebra and at Cucaracha. The slides at Culebra are on both sides of the waterway, occupying a length of 2,800 feet, while the channel affected by the Cucaracha slide is less than 2,000 feet long, so that out of a total length of 8.75 miles only 0.88 mile is affected. Another misconception that exists relates to the character of the slides. They have not been, except in part at Cucaracha, a slipping down of portions of a bank in order to reach the slope at which the material will stand. Slides of this character have occurred, but they were small in extent and easily handled. Those at Culebra are breaks resulting from deformation or crushing of underlying strata which, under changed conditions, could not bear the weight of the superimposed mass, and caused a vertical settlement or drop of the overlying material, which subsequently moved into the prism. Final rest will be secured when all the material that is in motion has been removed. As is shown by experience with smaller breaks that have occurred from the same cause, when the end is reached the final surface will be concave, or bowl shaped. When water was turned into the Cut on October 10, 1913, the channel was completed to full width and depth except at Cucaracha, where the steam shovels were making but little headway against the slide; three benches which had been left (one at La Pita Point, one on the east side near Empire, and one on the west side oppo- site Cucaracha) ; the inclines, one at either end of the Cut ; and the remains of two small slides, one on the east side, of the ''break" variety, and the other on the west side, a typical slide of clay which occurred prior to the removal of the steam shovels, both of which, between Empire and Culebra, were cleaned up by the dredges and have remained quiescent since. Cucaracha slide is on the east side of the canal south of Gold Hill. It began to give trouble as early as 1884, during the operations of REPORT OF THE GOVERNOR. 3 the French Canal Co., but all the indications pointed to a surface movement only. The French built an elaborate system of drainage to overcome the difficulty, and, while successful so long as work of excavation was suspended, further deepening of the Cut in the vicin- ity resulted in renewed activity, with complete destruction of the drainage system; the remaining part of this system was carried away by the slide in 1907. The slide gave trouble in 1906, when excavation proceeded through this section. The difficulties increased as the depth increased and in the autumn of 1907 became most for- midable. From this time until 1910 the difficulties became less, and it was believed that they had been overcome and that the clay re- maining would be supported by a rock dike which was uncovered and which apparently possessed ample strength to retain the mass above and back of it. On January 20, 1913, the rock dike broke at or below the bottom level of the canal and completely filled the prism mth clay and rock for a length of 1,600 feet, to a depth of 30 feet on the bank opposite from the slide, increasing toward the east on a slope of about 1 on 4. Steps were taken, by means of sluicing, to wash back as much of the top portions of the clay as possible into the valley on the east side of the ridge. As steam shovels could not cope with the situation economically and advantageously and as the remainder of the Cut was ready for the admission of water, this was allowed to enter and recourse had to dredges for the removal of the balance. The time within which a passage through the slide was cut, as well as the cost, is conclusive that this method was the most efficient and economical way of handling the material. In July, 1914, troubles in Mexico interfered with the handling of cargoes by the Tehauntepec route, and shipping interests were clamoring for relief. The dredges had secured a channel through the slide, and the Panama Railroad operated a line of barges through the canal between the terminal ports, but these could not handle the traffic. While the full depth and width had not been secured through the slide, the channel was sufficient for the passage of ship- ping, and consequently the canal was opened to commerce in August, 1914. Several movements have occurred since at Cucaracha, but they were handled easily and did not delay commerce until the last of August, 1916, when a movement occurred, bringing down material from the northeast corner of the slide area, and moved huge rock bowlders across the center line of the channel, so constricting it as to force a suspension of navigation on August 30, 1916. The larg- est mass of rock occupied a length of 65 feet. The bowlders required drilling and blasting operations in order to remove them. Holes 20 feet deep in a ffintlike substance were drilled at great expense of time and drills before they could be broken up sufficiently for the 4 THE PANAMA CANAL. dredges to handle, and the closure of the canal lasted eight days, although two small ships were passed through in the interval. Gold Hill is of basalt, thrown up in a molten state through the sedimentary deposits that already existed and poured over the deposits on either side of the stem, giving to the vertical section the general shape of a mushroom. The portions projecting beyond the stem, being left unsupported, broke when the material moved from under, and the rock thus detached came down with the rest of the material at Cucaracha, This same action occurred on the opposite' side of Gold Hill within a few months after the east Culebra slide became active. A slide developed during the excavation in 1906 north of Gold Hill on the east side of the Cut. This was a typical slide, a surface movement which flattens the slope, and slides of this character had occurred in this locality during the French occupancy. The French endeavored to overcome them by drainage tunnels, but the mate- rial through which they were built was too fine grained to permit the free passage of water, and the method was not continued. In 1907, at the village of Culebra, the type of slides designated "breaks" first manifested itself. When the excavation had reached a depth of 135 feet above the finished bottom level, a crack appeared in the surface of the undisturbed ground, extending from one point on the prism slope to another. Subsequently there was a subsidence of the surface on the side of the crack farthest from the prism, accom- panied by an upward movement of a portion of the bottom of the excavated area a little distance from the foot of the slope. This was followed later by a settlement of the mass between the crack and the Cut, which ultimately slid into the prism. The first break affected but a few hundred feet, but as the depth of excavation increased the breaks became more extensive both in length and quantities of material involved; then they occurred on both the east and west banks, the upward movement along the bottom of the excavation continuing until the area affected extended for a length of 2,000 feet north of Gold Hill. The borings of record failed to disclose any weak underlying strata. The cause undoubtedly was the unequal distribution of the pres- sure exerted by the adjacent banks. Such being the case, it fol- lowed that if the height of these banks were reduced the movement would be lessened, and if reduced sufficiently would cease entirely. Subsequent events proved this to be correct. The banks were light- ened by taking material from the top, and there resulted final slopes through this portion of the Cut of 1 on 1^ to 1 on 6^ for the east side and from 1 on 2.46 to 1 on 4.35 for the west side; the slopes con- sisted of a series of steps. The upheaving of the bottom ceased REPORT OF THE GOVERNOR. 5 entirely, as already noted, and the canal prism was carried to full depth and width throughout the entire 2,000 feet. Toward the close of the dry season, in April, 1913, a crack ap- peared on the east side opposite Culebra, about 1,300 feet from the prism, in an old French dump. It was parallel to the canal, did not join the banks, there was no breaking up of the banks between it and the Cut, nor any subsidence — in short, there were none of the indications that accompanied previous breaks. The geologist be- lieved that it was due to the deformation of the underlying strata and advocated lightening the banks by sluicing and steam shovels, which was done. While this work was in progress the crack gradu- ally closed, and though the surface between the crack and the Cut was in places noticeably below the level of the surface to the east of the crack, the closure was construed to mean that a condition of equilibrium had been reached. The canal through this section was completed, the water was turned in, and no further trouble was anticipated in this section. A crack had existed for some years at the foot of Zion Hill, south- east of Culebra. The hill was pronounced geologically secure against any movement, and when the material was dug away from the upper portions of this bank, and the slopes of the final bench reached the crack, it did not increase and there was no movement. Just prior to turning in the water a rock slide occurred north of Gold Hill on the east side, increasing somewhat with the admission of water, causing no change, however, in the crack on the top. A similar slide occurred on the west side after the prism filled with water. In both instances the movements were typical of the ordinary slides — an adjustment of the slopes. The material was easily han- dled by the dredges and the channel freed of all obstructions before the canal was opened to navigation. This condition continued until October 14, 1914, when, without any warning, a section of the east bank north of Gold Hill settled vertically 20 feet. This section measured 2,000 feet along the prism face, and extended back about 1,000 feet from the axis of the canal, generally along an irregular curved line, but did not extend back to include the crack that had developed in 1913. The top of the bank was from 300 to 350 feet above sea level. After the settlement the upper surface of the portion that broke away remained practically parallel to its original position, and the existing benches of the upper part of the slide had not changed their relative positions, though they were badly broken up, but the lower strata were squeezed out across the canal, reducing the depth of water from 45 feet to 9 inches at one point within an hour's time. Subsequently the broken mass moved into the Cut, as was the case with other breaks. Navigation was suspended for a week, but after this and until August, 1915, the dredges were able for 6 THE PANAIMA CANAL. the most part to keep up with the material as it came down, and would have been able to maintain such condition had not a movement occurred on the west bank, necessitating work on this side to the detriment of the east side. A crack was foimd on the slope of Zion Hill in Jmie, 1914, higher up than the crack already mentioned, but observations made upon it showed no movement, and the solidity of the hill was never doubted. Subsequent to the break on the east side, a gradual but general breaking up of the west bank followed. The crack on the slope increased in size and new ones developed farther up the hill^ imtil finally one extended to elevation 480 above sea level, the limit of the present break. The movement into the Cut from the west bank occurred early in August, 1915, when a section of Zion Hill broke away and settled down. The edge of the break on this side is also a curve. The movements from the two sides were toward the central portion of the inclosed area, and at this central portion the bottom was forced up, at first forming an island, then a peninsula projecting from the east bank, and finally an isthmus entirely across the channel. The barrier increased until it had a length of 255 feet along the axis of the canal and an elevation of 65 feet above the surface of the water. Tlie movements on the two sides are entirely different in character. On the east side a settlement of a mass occurs, the top generally tilting backward from the prism, with a shoving out below. On the west side, for the most part, rock masses become detached and gradually settle down vertically, with very little lateral movement^ pushing out the material along the prism face. When the break occurred on the east side it was realized that it would extend eventually back to the limiting cracks, and that all the material lying above some surface, concave in shape, unless removed, would eventually enter the prism. It was impossible to handle any of it by hydraulics away from the Cut, and the only other method would be by steam shovels. These could only operate on firm ground, and would necessitate the establishment of dimips. The number of shovels that could be worked would be limited, and con- siderable excavation would be required before the sliding material could be attacked. The dredges were capable of and were removing over 1,000,000 cubic yards per month without any of the difficulties attending steam-shovel operations, and what could be accomplished by the latter would be relatively so small and the cost so high that the idea of introducing steam shovels was abandoned and the decision reached that the material must be removed from the canal side by the dredges. From experience with other breaks, it was known that the move- ment would not be continuous. A settlement occurs, by which REPORT OF THE GOVERNOR. 7 material is pushed into the prism ; the movement is at first heavy and rapid, gradually diminishes, and finally ceases. This condition of rest is distm'bed either by the rains or by the operations of the dredges cutting into the banks. As all the material liable to move must be taken out by the dredges from the Cut, there would come a time when the machines would be idle, waiting for a movement to give additional material for them to handle. The judicious application of hydraulicking the bank would avoid such a condition, conse- quently pumps for sluicing operations were installed on two barges. These have been used for cutting and maintaining surface drainage and for washing down material to the dredges, when the conditions warranted it. The finished section from Gold Hill north left an enormous mass of hard rock on the east side and at the northwest corner of Gold Hill. When the break occurred in 1914 this mass of rock was moved slowly into the prism, but finally came to rest and seemed to hold the material back of it, limiting the area of interference in the channel. It stood up boldly 'for nearly 100 feet and was designated by the working force as ''Gibraltar/' which designation will be used when referring to this mass of rock. The slipping of the material into the Cut removed the support to the mushroom portions of Gold HiU on its north side, which broke off in large masses and followed down diagonally toward the prism, the effect being similar to that described as having taken place at Cucaracha, and the direction of the movement was due, no doubt, to the retaining effect of "Gibraltar," though this took up slow move- ments at times when the heavier masses back of it were disturbed by subsequent settlements. If the width of the prism through the slide section remained as fixed for the project — 300 feet bottom width — every movement that occurred on either the east or west bank would contract the channel, and should a movement occur in both banks at the same time it would probably result in closing the canal to navigation. The neces- sity of restoring the channel to permit the passage of ships and the maintenaaice of navigation were the main considerations. An addi- tion to the width sufficient to take care of material pushed in by subsequent movements, thereby increasing the chances of main- taining a channel, was considered advisable until all the loosened material had been removed. This led to a modification of the pro- jected width, which was increased to 500 feet, 100 feet on either side of the original prism lines. The conditions as they existed then — in November, 1915 — ^found the canal closed to navigation indefinitely. There was across it an isthmus 250 feet long in the direction of the axis of the canal, the top of which was about 65 feet above water; the dredging operations 8 THE PANAMA CANAL. were confined to the north of this isthmus, working toward the south, with arrangements made for washing down the material in case it was advisable to accelerate the motion of aiiy part of the sliding area, and with the project modified so as to give a completed width north of Gold Hill of 500 feet. In Occober, 1915, the President of tlie United States was advised by a member of the National Academy of Sciences — which was organized by an act of Congress to give expert advice to the President and Congress on scientific matters — who stated that one of its mem- bers had made an extensive study of earth slides in tropical countries, and was convinced that there were relatively simple ways by which they could be stopped, and suggested that a committee of mining engineers and geologists of the academy be appointed to consider his propositions. In consequence of this, the President of the United States requested that a committee be appointed by the National Academy of Sciences to '^ Consider and report upon the possibility of controUing the slides, which are seriously interfering with the use of The Panama Canal." From the correspondence it appears that at a meeting held in New York, "* * * the hope was repeatedly expressed that an effective solution may speedily be found." The coming of the committee was welcomed on the Isthmus, for so much misinformation had been sent broadcast, doing more injury to the canal than the closing of it by the slides; confidence had been upset ; and io was hoped not only that a remedy would be forthcoming but that the report of the committee would be able to restore con- fidence in the project, especially as those connected with the work knew that the methods adopted would overcome the difficulties for good and all, given the time and money, and that the waterway would be all that had been expected. Probably the greatest injury done the canal was through Prof. Benjamin Le Roy Miller, Ph. D., who occupies the chair of geology at Lehigh University. On returning to New York from Costa Rica he stayed here a couple of days awaiting a steamer. He was given every facility to examine the slides at Culebra, which were then at their worst, and he is reported to have said for publication on his arrival in the United States that he had made a " thorough examina- tion of the slides," and the conditions found were as follows — the statement appearing in quotation marks in the press item: At the Culebra Cut * * * cracks have formed over 1,300 feet back from the canal, and all of the ground intervening is moving toward the Cut. There is no doubt that much rock, now apparently stable, also will move, as its support is withdrawn by the removal of loose earth and rock. Before the canal can be said to be completed and permanently opened to traffic, the amount of material that must be taken out will not fall far short of the amount already taken from the Culebra Cut. Transportation companies planning to use the canal should realize that they must not expect uninterrupted service for several years. During the dry season the canal REPORT OF THE GOVERNOR. 9 may be opened, but it is certain to be closed during the rainy season when the earth is soaked with water and its movement toward the canal facilitated. In view of the extent of the material that has now started toward the Cut, it seems that steam shovels should again be employed. Practically all of Gold Hill and much of Zion Hill must be removed, and to wait until the earth breaks loose and enters the Cut where the dredges can attack it seems unwise, and unquestionably longer delays the completion of the project. If dredges alone are employed, as at present, the canal may be kept clear during the months when rainfall is lightened, but for many years to come the rainy season is almost certain to cause such slides as to close the canal for weeks or even months. The "thorough exammation " occupied fully three or four hours of his time. The position that he occupied in one of the leading uni- versities of the United States gave credence to his statements, which were copied broadcast, and commented upon editorially to the detri- ment of the canal. His dire predictions were naturally unsettling to shipping interests, which were guided by them to some extent in routing their commerce elsewhere. It was anticipated that the committee from the National Academy of Sciences would make a more thorough examination than Prof. Miller had done, and it was hoped that, as a result, the statements of Prof. Benjamin Le Roy Miller, Ph. D., would be found to be what we considered them — erroneous, unwarranted, and unfair, and help restore the confidence that he had helped to destroy. The preliminary report by the committee of the National Academy of Sciences was submitted to the President in January, 1916. At that time they expected that their final report would be completed in April, but up to date it has not been received. The preliminary report will be found in Appendix N. It will be noted that the state- ment made by Prof. Miller, that practically all Gold Hill and much of Zion HiU must be removed, is not concurred in; and in this connection it should be remembered that a committee of this character expresses its opinions guardedly, for whatever happens they must be found on the right side. They advocated, as a matter of scientific interest, the making of an accurate triangulat,ion of the hiils in question — Gold, Contractors, Culebra, and Zion — which has been done. By checks made at frequent intervals the slightest movement on the part of any of the four hiUs would be disclosed at once. No movement of any kind has taken place. The committee expressed the belief that every available and prac- ticable device for controlling the water, both on the surface and under- ground should be employed, and to this end advocated covermg the slopes with vegetation to prevent surface wash, closing peripheral cracks, draining undisturbed and threatened areas, and draining by tunnels. For several years the expedient of covering the slopes with vegeta- tion has been carried on, starting under the direction of Dr. Pittier, of the Smithsonian Institution. Where the surface of the ground is 10 THE PANAMA CANAL. in motion, as in the case of active slides, the roots are disturbed, and the steady growth of vegetation is impracticable. Trees and vege- tation of all kinds growing on the surface of the ground which broke in October, 1914, were carried down the shde and exercised no deterrmg effect whatsoever. On shding ground there is not sufficient time to plant anything and no good would be accomplished. Where the banks consist of the red clay of the country, it is only after con- siderable difficulty that grass of any kind can be grown on them. Vegetation stops erosion; on this account the work was undertaken and is bemg carried on. When peripheral cracks occur in rock with sufficient earth covering they may be effectually closed by the use of a hydraulic grader, as was done in an incipient slide on the west bank of the canal near Las Cascadas, The sluicing down of the earth into a uniform slope not only fills the cracks and prevents the access of surface water into them, but facilitates the drainage by providing a ready means of run-off into the canal. This method, while apphed with good results at the north end of the East Culebra slide, so long as the material is at rest, a subsequent movement develops new cracks and irregu- larities so that until all loose clay and rock is removed and the final slope reached, the relief is temporary only. Where there is very little earth covering, as is the case on Culebra HiU, and where the cracks are wide and extend a great depth in rock, it is not practicable to close them permanently without expense that is disproportionate to the results obtained. In compliance with the expressed wishes of the committee while on the Isthmus; subsurface tile drains have been installed within an area on Culebra Hill as an experiment. Also, as suggested by the committee, the fault fissure under the hard Obispo tuff on the north side of Contractors Hill has been sealed and a concrete-lined drain constructed, draining the surface water into the canal, with a view to the protection of the Cucaracha rock beds adjacent to this portion of Contractors HiU. It is admitted that if the water could be entirely excluded the earth movements would cease, but unfortunately this is impossible. With the heavy tropical downpours the best that can be done is by drainage, to carry away what falls as rapidly as possible, but ground water can not be eliminated. So far as concerns ground water, the construction of the canal has created entirely new conditions. The old tributaries of the Chagres River and those of the Rio Grande, which formerly were natural' drains, are now well above the water surface of the canal, and the canal has become the drainage channel for the countr}^ for miles on either side. Even assuming that were it possible to devise a system for getting rid of ground water, it must still exist below the surface of the water in the canal itself. The slides REPORT OF THE GOVERNOR. H in question affect the banks for a considerable distance down, prob- ably below the bottom of the canal, and if ground water be primarily the cause, then it can not be removed from the strata at which the trouble starts. Surface drainage was maintained throughout the period of dry excavation. The adjacent country on either side of the canal was drained through the east and west diversions, which continued to act as drains, discharging their accumulated waters into the Chagres. In relieving the pressure, force pumps on barges have enabled the washing down of part of the material, as already explained. The hydraulic grader which was constructed in July, 1914, and put in commission in August, 1914, was built especially for opening chan- nels to expedite surface drainage at various points along the line of the canal, and to maintain them, and this work has been carried on, although suspended south of the slide, due to the interruption and shut-off of the channel last fall and winter. So long as the slides are active and the configurations of their sur- faces change as rapidly as they now do, it is impracticable to open and maintain the permanent drains recommended in the moving areas. When equilibrium is restored, and as a means of promoting permanent stability, the drains of a permanent character should be constructed and maintained. Drainage by tunnels has been considered in connection with data obtained since the committee's report was written, as the result of experiments suggested by the chairman of the committee. Dr. Van Hise, through whom the services of Prof. Warren J. Mead, of the University of Wisconsin, were secured, and who was assisted by Mr. Donald F. IMacDonald in making tests of the rock formation in which the east and west Culebra and Cucaracha slides have occurred. I have received from Mr. MacDonald, the geologist, a brief report, hereto appended, marked ''Appendix O," which states the result of the experiments, as follows: Twenty-one average samples of the Cucaraclia or sliding formation were taken from below the water level of the canal. These samples, completely saturated, con- tained 12.20 per cent of water by weight, or 27.8 per cent by volume. The 16 average samples taken from well above the level of ground water, where the rocks were much jointed and fractured and, therefore, perfectly drained, contained 10.60 per cent of water by weight. As shown above, 12.2 per cent of water by weight fills all of the pore spaces of the rock; therefore, 10.6 per cent by weight fills only 87 per cent of them, leaving 13 per cent of the total pore space as having been emptied by drainage and by drying. Now, 13 pei* cent of 27.8 per cent is 3.6 per cent of the total volume of the rock. This shows that natural drainage of the most perfect kind would not remove more than 13 per cent of the water by weight, equivalent to 3.6 per cent of the volume of the rock. However, most of the samples from the drained rock were taken very close to the surface, so that very likely they lost some of their water through drying out by the heat of the sun, for the dry season was more than a month old at the time they were collected. 12 THE PANAMA CANAL. These facts show that while the sliding rocks have a high percentage of pore space, the pores are mostly of capillary size and are filled with water which obeys the laws of capillarity and which can not, therefore, be drained off. These experiments defi- nitely established that all ciu-es by drainage which had been offered to and urged on the canal authorities were absolutely futile, and the money which might have been wasted in worthless tunnels, wells, and acres of asphalt covering, was saved for the only remedy that could bring permanent cure under the circumstances — dredging. Before considering the suggestions tliat have been made for con- trolVing or preventing the shdes other than those aheady mentioned, it may be well to state what was attempted by the canal forces in this direction prior to the occurrence of the slides which are now active. During the excavation of the Cut 22 slides and breaks of various extent occurred. The steps taken to protect exposed slopes by vege- tation have been noted. It was believed that piles driven through the loose material into firm ground below and tied at the tops might check the movement, and this was tried at four of the slides, but without success. In some instances the piles were carried bodily down the slope; in others the underlying material, moving faster than the upper portion, inclined the piles away from the Cut, and in cases where the top surface moved faster than at the bottom, they inclined in the opposite direction. The remains of these piles can be seen at the present time in some of the areas so treated. It was thought that in case of clay slides heavy riprap dumped on the surface would find its way through the loosened material to firm ground and check the movement, but this method was found as use- less as the pUing. Most of the riprap rock was taken out at the foot of the slope as the excavation proceeded. Experiments were made by concreting the face of the prism to prevent the disintegrating effect of the air on some of the softer rocks ; this was done by use of a cement gun, by plastering the surface with cement mortar and by reinforced concrete, anchored to the side of the prism with pieces of rail. None of these methods was satisfactory or durable. The rem- nants of the French drains, which proved inadequate, were dug out at the bottom of the prism. The conclusion was reached that the only cure was the removal of all loosened material as it came into the Cut, and in case of breaks to relieve the weight, where possible, from the upper parts of the banks by steam shovels or sluicing operations. In considering any method for stopping the slides some concep- tion must be had of the enormous amount of material involved, as well as the method in which it acts. The banks at present giving trouble are from 300 feet to approximately 550 feet above sea level, and extend back 1,300 to 1,800 feet from the faces of the prism, and from these farthest points to the water surface the entire mass is broken for a depth extending at least to the bottom of the canal. As already explained, the movement is by fits and starts, sudden at BEPOET OF THE GOVERNOR. 13 fii-st and gradually subsiding, with renewed activity after a period of quiescence. For instance, in August, 1916 a general movement occurred at the east Culebra slide and consisted of a settlement from 20 to 25 feet vertically down at the rear portion of the area affected, some 1,300 feet from the prism, by which a mass of material from the lower part was projected into the Cut beyond the center line, reducing the depth of water along this line an average of 5 feet. Because of the width of the new channel, as well as the depth, navi- gation was not interrupted, but some idea may be had of the enor- mous amount of material that must be held back by any artificial construction or device smiilar to those which have been proposed, and the impossibility of their construction must be recognized. Suggestions most frequently made have been along the line of sowing vegetation and of properly draining the area. These have aheady been considered. To sink a number of pipes and apply steam for drying out the subsoil would be prohibitive on the score of expense, even if it were practicable. It would be impossible to drive and hold such pipes through the material in case of motion. Pipes sunk for the purpose of pumping out the water are equally imprac- ticable and impossible. From the experiments conducted by Prof. Warren J. Mead and Mr. MacDonald all the water could not be ex- tracted by this method. Pihng the entire area at regular intervals and tying the piles to anchors driven in the firm ground can not be done, nor would it secure the result anticipated by the proposers of this scheme. The construction of retaining walls would require the excavation of material to secure the foundations, necessitating the removal of all the material in motion, when the need for the retaining wall would no longer exist. There is no form of construction that could be designed that would hold back the superimposed mass while the excavation for the foundations was in progress. The construction of inverts to hold down the bottom of the prism is impracticable and impossible. Wire netting rolled over the bank and held in place by stakes' would not prevent the movement, but would seriously interfere with the dredges in removing the material littered up with sections of wire mesh, which would break loose with every movement of the sUde. Consohdating the mass by injecting grout would also be impossible; the pipes could not be driven to firm ground below and the earth and rock, as it now comes into the Cut, can be much more easily handled than would be the case were this material solidified by cement. It was suggested that the slopes and the surface of the ground adja- cent to the Cut be covered with asphalt, tar, or some preparation which would exclude water from the ground. This was also pro- 14 THE PANAMA CANAL. posed by a member of the committee from the National Academy of Sciences. That the committee did not include it among its recom- mendations seems conclusive that in its opinion it was not practicable, and no further comment seems necessary. A number of theories have been advanced as to the cause of the difficulties, among them that there exists a huge reservoir of water within the earth and the pressure therefrom produces the shdes. If this be so, the pressure being sufficient to break the ground would release the water and aUow its escape. All the water that is drained from the slide areas is accounted for by the rainfaU and by the escape of any ground water that the movement might hberate, and the theory is untenable. The mutual attraction of the large masses on either side of the Cut is assigned as the cause for bringing down the material, and yet another that a huge magnet that previously existed has been cut in two. The latest theory advanced appears in an article pubhshed in the New York Sun on June 18, 1916, by the Hon. Thomas Kearns, ex United States Senator from Utah, and repubhshed as Senate Document No. 525, Sixty-fourtli Congress, first session. He believes, "* * * that the trouble is all caused by subter- ranean gases formed in the earth which, when permitted to escape through certain channels or breaks in the earth, carry with them eruptive material, sometimes for a long distance, to the place of the least resistance." Coming from a man with such large practical experience, it undoubtedly carried conviction to the minds of many who read it. Since Senator Kearns' s examination was more thorough than that made by Prof. Benjamin Le Roy Miller, Ph. D., it is com- forting to note from his judgment also that Gold and Contractors HiUs are not likely to faU into the Cut. Senator Kearns is in error when he states, ''Since it (the canal) was first opened to navigation on August 14, 1914, it has been closed and out of commission virtually two-thirds of the time." The canal was opened to traflB.c August 15, 1914, and up to June 18, the date of the article, the canal was closed 232 days out of 656 days, or approx- imately one-third of the time, instead of two-thirds, as stated. Another error is that there was an upheaval in the bottom of the Cut at some other point than the Culebra section. At no portion of the canal has there been any upheaving except in the 2,000 feet north of Gold HiU. This upward movement first occurred when the excava- tion had reached elevation 175 feet above sea level, or 135 feet above the finished bottom of the canal. The upheaval, as the result of the present slides, reached an elevation of 65 feet above the water surface, or 110 feet above the bottom of the canal. In no case was there a movement at the bottom that was not preceded by a movement in the adjacent bank. The movement in the bottom ceased entirely in EEPOET OF THE GOVERNOE. 15 1913, when the side slopes were made sufficiently flat to reduce the pressure exerted by them to less than that required to accomplish this upward movement. The upheaving in the bottom occurred again subsequent to the break in October, 1914, when the huge masses of the banks crowded toward the axis of the canal and dis- turbed the condition of pressure that existed prior to the occurrence of the shdes. Part of the shoaling in the canal is undoubtedly due to the resistance to the motion of the mass at some part of the bottom, which throws part of the slide itself upward with the effect shown. According to Senator Kearns's theory, gases forming somewhere in the interior of the earth in escaping carry with them eruptive material to the place of least resistance, or in this instance through the bottom of the canal. The breaks, which produced fissures several hundred feet deep, liberated no gas. With a pressure sufficient to accomplish such destruction of the structural formation of the rocks, apparently the gases returned to their storage to attempt later a forced passage through the bottom. We unconsciously endeavored to assist their efforts by digging away 110 feet of their container, but even this did not induce the gases to come forth; thus far there has been no evi- dence of escape anywhere along the hne of the canal, nor has there been any upheaving movement anywhere except in the Culebra district, where the slides occur. So long as there is no movement in the banks we are able to reach bottom grade and keep it. Under the circumstances, those on the work stiU adhere to their belief that subterranean gases have nothing whatever to do with the movements that have occurred. The methods proposed for securing a channel through the. slides and to maintain it, adopted in October, 1915, were laid before the committee of the National Academy of Sciences, including the sluicing operations proposed on the west side, but no suggestions were made which modified the plan in any way. The various propositions made by a number of people seeking to help us in our troubles were care- fully considered, as were also the theories advanced setting forth the probable causes. There were a number of letters, the writers pro- posing, for suitable monetary consideration, to cure the slides, but these were filed. None of the suggestions or theories tended in any way to change the plans adopted. The dredges did their work so well that a channel was cut through the Isthmus connecting the two banks, of sufficient size to pass the small ships still tied up and awaiting transit. By April 15, 1916, a sufficiently stable channel had been secured to warrant opening the canal to navigation, and the transit of shipping has continued to date. Except at "Gibraltar" the waterway is 500 feet wide with 40- foot depth over the greater part, this depending on the movements that occur in the banks. So far as the Culebra slides are concerned, 16 THE PANAMA CANAL. the worst is over; the intervals between movements are becoming greater and the quantities of material less; the only danger being at "Gibraltar," but it is hoped that the excavation continued along the lines contemplated will enable the widening of this section to the adopted prism line without interfering in any way with the transit of shipping. The reopening of the canal was at the beginning of the rainy season, and thus far the rainfall has been above the normal. The recent movement at Cucaracha was, as usual, the unexpected, coming as it did from the high ground in the northeast corner of the slide area. The difficulty attending this was not a question of amount of material, for the dredges could cope easily with the movement on this score; the hard flinty rock was difficult to break up, and caused irritating and aggravating delays. As predicted at the time the great Culebra movements occurred, the slides will be overcome finally and for all time, notwithstanding the calamity howlers and in spite of the disastrous predictions of the *' know-it-alls." o "y-d-'i',', :-V-A t'*'^??' ^-vf Vj