If, therefore, it is decided to disregard the recommendations of the majority of the Board of Consulting Engineers, and to build a lock canal, then it is to be earnestly hoped only such form of lock canal will be authorized as will be admissible in connection with the construction of a dam at Gamboa rather than at Gatun. While for certain purposes and under certain conditions earthen dams of large dimensions carefully formed are permissible, in this case it is not believed that such form of construction should be seriously considered when it is possible to secure a masonry structure founded on bed rock; particularly when the work under consideration must be supposed to possess permanency, and is being erected as a monument to the engineering skill of our modern civilization. There is no urgency that to my mind would justify the great risk of earth dams at Gatun or La Boca. The next important matter to consider and decide is whether the canal shall be constructed under the present method of management or whether a contract for the work shall be made with a single contracting firm. In the latter case the specifications, of course, should be of the most broad and general nature, leaving all detail engineering plans to the engineers of the contractor in order that he may have the fullest latitude in immediately meeting and overcoming such local difficulties as from time to time are sure to arise. After the contract is let, there would, of course, be no reason for retaining a cumbersome governmental organization in reference to the work, for there is no doubt that the Corps of Engineers of the United States Army could most efficiently supervise the contractor engaged upon the work. All the governmental functions, including policing and sanitation, could easily be performed under the control and direction of the governor of the Canal Zone. It can not be doubted that these two methods, if adopted, will give entirely satisfactory results. The question will naturally arise in doing the work by contract whether there are any engineering organizations competent to enter into such a contract and to construct a work of this magnitude, and such a question must be answered in the affirmative. Several wellknown organizations are quite capable and competent to handle a work of this character, and there is no good reason why they could not be induced to make bids for it, if the Congress in its wisdom decides such a method of management of this great work is preferable to that which has existed for the last two years. In considering the question of additional time required for the construction of a sea-level canal the prompt and efficient utilization of the Panama Railroad is a matter of very great importance; for if the railroad is provided without unnecessary delay, with the very best modern facilities and equipment, including double tracks with abundance of sidings, shops, wharves, docks, and warehouses, and especially with the latest and most approved appliances for transferring cargoes from ships to cars and from cars to ships, very many of the advantages the world's commerce would derive from the completion of the canal will be at once afforded to it. Indeed, in many cases of goods shipped from American ports destined to the west coast of South America, it will probably be found advantageous for them to go in a single ship to Colon and being transferred by the railroad to Panama, be reshipped in smaller vessels plying from that port to the different ports to which different parts of the cargo may be consigned. that its decision will meet the expectations of the people in all respects and satisfy the just pride that their country has undertaken the task of conferring upon the world the benefits of this great enterprise. Senator KITTREDGE. When you arrived at the Isthmus about the 1st of June, 1904, you found engineering parties there that had been operating on the work? Mr. WALLACE. Yes, sir. The line from Colon to Gamboa was covered with engineering parties; and they were first charged with- a verification of the French topographical maps, and second, with making borings. Senator KITTREDGE. Where were the borings made? Mr. WALLACE. There was one party at Colon, under Mr. List; a second at Gatun, under Mr. Nichols; a third at Bohio, under Mr. Dauchy, and a fourth at Gamboa, under Mr. Ely. These several parties were again subdivided into smaller parties. Senator KITTREDGE. Please tell us the result of the explorations and borings at Gatun especially, and also at Bohio. Mr. WALLACE. In order to explain that situation I will state that when I first took charge I understood that the type of the canal had been practically established by the Spooner Act, although some deviation might be permitted from it; and I had read a paper by Mr. Ward, published in the transactions of the American Society of Civil Engineers, which has been made part of your record, and I was very much taken with the idea of a dam at Gatun. The first idea I had, after I had spent a week or so on the Isthmus and looked the situation over generally, was that that was the proper locality for a dam, if a lock canal was constructed, provided suitable foundations could be secured for it. Senator KITTREDGE. Why was that? Mr. WALLACE. In figuring out the various elements of cost, it gave a lock canal with the proper depths and widths for less money than the estimates made under the Spooner plan. That was the principal reason. After we had made a very few borings at Gatun, however, we struck one of the gorges that are shown on the cross section that appears in this exhibit before the committee and found this loose, permeable stratification extending down to about 179 or 180 feet below the sea level, containing sand and freely water bearing. That convinced me that there was no hope of finding any suitable foundations for a dam inside of any reasonable distance, so I put my parties. temporarily on other parts of the work. You Senator KITTREDGE. I wish you would explain in detail just what was done in making borings at Gatun and what was developed. may use maps if you wish. Mr. WALLACE. I do not see your cross sections here. I do not remember how many borings were made, but we made quite a number. [After examining maps. I am not able to tell from this particular plan what part of these borings were taken under my jurisdiction. The CHAIRMAN. I think all the borings are noted on this plan. I think one of the engineers a few days ago stated that fact. Senator KITTREDGE. Some were made after Mr. Wallace left. The CHAIRMAN. I think a number were made after you left, Mr. Wallace. Mr. WALLAGE. The railroad is on this side of the gorge [indicating]—that is, this cross section is a cross section across the valley, looking north, and some of the first borings that were made went down in this gorge about 179 or 180 feet. We made others that only went down a part of that distance, but as soon as I discovered that there was a gorge there and that that depth was below the possibility of finding a foundation with which a permanent contact could be made, or to which the foundation of a dam could be taken, I temporarily abandoned those borings and went to work with the same. party and tried to find the character of the material through here, with the idea of making a cut-off in order to shorten the canal. That was afterwards abandoned, however. After the Commission came down in August they were not satisfied in regard to my theory of the continuity of this gorge, so then we went to work and kept at it continuously from that time and took these other borings which you see here in order to determine, if it was possible, that we could find some place where the indurated clay was not so deep as it was at the point first selected for examination. In other words, to present the matter more clearly to you, the principle I was working on was this: That in a work of this magnitude it would not be safe to construct any dam to hold back the head of water that would be necessary at that point unless we could go to bed rock with our foundations. That we had decided on as a fundamental principle. When we found that the gorge existed there, I could see no use of further explorations. Senator SIMMONS. Do you mean, Mr. Wallace, that it is necessary that the whole dam should rest upon a rock foundation? Mr. WALLACE. No; not necessarily; but that you should be able at least to carry a curtain Senator SIMMONS. I mean for the safety of the dam. Do you mean that it is necessary that the whole of the dam should rest upon a rock foundation? Mr. WALLACE. No; not the whole foundation. But it is necessary—that is, in my own opinion-that you should carry down a contact, or what we call a curtain wall, to the bed rock or to some impervious material. Senator SIMMONS. The whole length of the dam? Mr. WALLACE. The whole entire length of the dam. Mr. WALLACE. That is, from one side of the valley to the other. Why, it is so as to cut off the percolation of any water underneath your structure. Senator SIMMONS. Is that what you call a core? What do you call that construction which you say must go down to the rock? Mr. WALLACE. If it is an earth dam which you are building on a rock foundation you put in what we call a puddle core. That is, you put in a core in the center of that dam that is impervious to water. Senator SIMMONS. Yes. Mr. WALLACE. If you desired to build a large earth dam in an alluvial valley you would want to carry that core down to the bed rock or to some impervious material. We generally call it a curtain wall. The CHAIRMAN. What you mean by the curtain is the wall made of concrete or stone, or whatever it may be, that comes next to the water, and then you fill it behind with earth? Is that it? Mr. WALLACE. No; I mean a subterranean construction, a subsurface construction that will go clear to the bed rock. Senator SIMMONS. What is that to be made of-masonry or timber? Mr. WALLACE. That can be of timber if it is entirely submerged, or it can be of concrete, or it can be of any material, of whatever nature, that will be permanent and that will, without any question, shut off the percolation or flow of water underneath your dam. Senator TALIAFERRO. That is, this curtain has no part whatever in the foundation except to prevent an underflow of water? Mr. WALLACE. That is it, exactly. Now, there are two things to be guarded against Senator SIMMONS. This curtain goes down to the rock and extends the full length of the dam? Mr. WALLACE. Yes. To make it clear to you, perhaps I can explain it a little differently. The foundation for a dam has to perform two functions. One is to support the structure upon which it rests; the other is to prevent the water from running through underneath it. Senator TALIAFERRO. And undermining it? Mr. WALLACE. Either undermining it or else exhausting your reservoir of its water supply. You may have a flow of water underneath a dam that may drain the dam area and still may not ruin your structure as a dam. Have I made that clear to you? Senator TALIAFERRO. Well, Mr. Wallace, if there was sufficient underflow to drain that dam, would it not in all probability impair the structure itself? Mr. WALLACE. Possibly, but not necessarily so that is, it might be possible to drain that water off absolutely and not be able to hold water in your dam and still not destroy the dam. But I would not take the chances on it if I were building the dam, though I can not say that it would not be possible to do it. Senator SIMMONS. Is it proposed to construct any such curtain as you now speak of at Gamboa? Mr. WALLACE. At Gamboa? No, sir; because at Gamboa the foundations themselves go to the bed rock. At Gamboa the primary rock foundation comes up-not the indurated clay, where you do not know what is underneath it, but the actual basaltic rock, of which the backbone of the continent itself is made. The deepest part at Gamboa is only at sea level. You only have to go 45 or 50 feet below the bed of the Chagres River to put the foundations of your dam right down on the bed rock, which is the backbone of the continent, and there is not any question at all about its integrity. Senator SIMMONS. But after you get to bed rock at Gamboa you propose to construct an earth dam there with a masonry core, do you not? Mr. WALLACE. No; not necessarily so. That was a detail that was left for subsequent determination. Senator SIMMONS. Has anybody suggested anything there except an earth dam with a masonry core? Mr. WALLACE. Yes, sir; I understand that the majority of the advisory board suggested a masonry dam, and a masonry dam is the thing, it seems to me, to construct there. The only reason that anyone ever suggested an earthen dam with a masonry core at Gamboa was from the fact that there was so much material to dispose out of Culebra that the material could be wasted at the site of that dam, and it would afford a place to put that material. As far as an engineering proposition is concerned, the proper thing to build there is a masonry dam. The strength of a masonry dam founded on the bed rock is a matter of absolute mathematical determination. There is no guesswork about it. You can logically reason from the integrity of one masonry dam to another masonry dam, because you have elements there that are what we call determinate. But you can not so figure on an earthen dam. An earthen dam is absolutely a question of judgment and opinion. You can build an earthen dam in Massachusetts or New York or Colorado that will stand a head of 85 feet of water, and it is no criterion at all that the same dam at Gatun or in South Africa or at any other place would stand it, because the conditions are never the same. I mean the conditions under the surface. That is a matter of what you may call engineering judgment if you are in favor of an earth dam, and you may call it engineering guesswork if you are not. Senator TALIAFERRO. Mr. Wallace, is not this earthen dam which is proposed by the minority at Gatun a dam of unusual strength? Mr. WALLACE. Yes; it is; but as I said awhile ago, the unusual size that you make that dam may affect its integrity as a dam if there is no water flowing under it and if it is on a proper foundation. But there are two gorges that are underneath it. The deeper you go in those gorges the more water-bearing the material is. You find the same mass of loose gravel in the bottom of this gorge here that we found in the bottom of the gorge at Bohio, a really water-bearing stratification, practically a subterranean river. Now, when you add to that a pressure of some 38 pounds to the square inch, due to this 85 feet of head of water which is behind this dam bearing on this water to press it through that stratification, no engineer can tell you what is going to happen there. Senator SIMMONS. Mr. Wallace, I want to see if I understand you. If I understand you, your position is that you can not guarantee the safety and integrity of an earth dam unless it is either built upon a rock foundation or unless there is a curtain going down from the surface, through the subsurface, to a rock foundation? Mr. WALLACE. Yes, sir. Senator SIMMONS. That is your position? Mr. WALLACE. That is my position. Senator SIMMONS. And that curtain must extend the full length of the dam? Mr. WALLACE. The full length of the dam; yes, sir. Senator SIMMONS. That is, not only across those gorges-down where those gorges are-but down where this indurated clay is? Mr. WALLACE. It must go into that. If this indurated clay is all indurated clay, if you get a good foothold into this clay it is a proper foundation. |