Page images

Mr. WALLACE. That one is about 1,800 or 2,000 feet across, and this one is about—a little over a thousand—about a thousand.

Senator DRYDEN. Yes; thank you. I did not quite get your point when you said that certain conditions might make a dam safe in Massachusetts but would not apply on the Isthmus.

Mr. WALLACE. Yes, sir.
Senator DRYDEN. I did not quite get that point.

Mr. WALLACE. What I meant by that was that there is no similarity in respect to the foundations.

Senator DRYDEN. Yes.

Mr. WALLACE. As far as the constructing of the dam itself is concerned, after your foundations are secure, if you construct a dam with reasonable care, with the same kind of material, and see that the layers are all properly put in, you can construct your dam itself as well in one place as you can in another. But what I meant to say was that because an earth dam had a proper foundation or was on a material that was not permeable by water in Massachusetts, it is no sign, if you construct a dam on the Isthmus, that you would find the same conditions occurring underneath the surface. You understand what I mean?

Senator DRYDEN. Yes.

Mr. WALLACE. There are two elements in the earth dam proposition. One is the structure which we intend to make, the elements of which can be determined. The other is that part of the structure which nature has made and which is not the same in one locality as it is in another. You might not find in the whole wide world another condition exactly similar to this.

That is the point I was trying to make—that the conditions underneath the dam in Massachusetts were no criterion as to what the conditions would be underneath the dam at Gatun, unless they were found to be identical.

Senator DRYDEN. The depth of this dam is about a half a mile, as I understand, from the head to the end of it?

Mr. WALLACE. Well, yes. Here it is, underneath here, on this lower map.

Senator DRYDEN. I think it has been testified that it is about a half a mile.

Mr. WALLACE. Yes, sir.

Senator DRYDEN. Is not the fact of that enormous depth, which I understand to be entirely unprecedented, far beyond anything that has ever been constructed before, a very important factor as furnishing a resisting force for the seepage of this water?

Mr. WALLACE. No, sir.

Senator DRYDEN. You hold it would make no difference whether that dam is of such a depth as that or smaller ?

Mr. WALLACE. Except this: Except so far as it would make a longer area between where the water might reach this substratifica

tion and where the water might come from, and increase the friction : due to the flow of water through the material. If that material com

pressed this gravel down in here it would be another proposition. But experience has shown us—at least my experience has shown methat the weight of that dam on top of this material would have no effect whatever on the flow of water through this gorge below here.

PO-VOL 3–06

[ocr errors][merged small][ocr errors]


It may compress some of the upper stratifications in which there is vegetation or alluvial matter.

Senator Morgan. By“ the gorge below here” you mean the deepest gorge?

Mr. WALLACE. Yes; the two deep gorges; the two gorges at Gatun.
Senator MORGAN. And this is the deepest one?
Mr. WALLACE. Yes. The same thing would apply to the other one.
Senator MORGAN. Yes; I merely want to get the record right.

Mr. WALLACE. The compression would take place in the upper stratifications that are made up of vegetable matter or of alluvial matter, and the effect of those compressions will be an inequality in the settlement of your dam, and the probabilities of cracks and breaks in it in line with the edges of these gorges. But the pressure of that dam will have no effect whatever as to the flow of water through this water-bearing stratification in the bottom of the gorges.

Senator DRYDEN. Would not the fine matter which washes down in the silt fill up the little, infinitesimal crevices in this alluvial matter, so as to constantly make it more water-tight?

Mr. WALLACE. Under some conditions it might; under other conditions, no.

That, in fact, is such an insignificant proposition that it is not strong enough to be an element upon which to base a decision of this kind. It has not done it so far. You find the deeper you go here the coarser this material is and the more water runs through it.

If a dam is built here, the possibilities are, you will find, that silt may never come in against the exact dam itself. It might not for ages; it might not for hundreds of years, because it will come in from the side creeks and will be deposited wherever the water is still, and there will be very little that may come down against this dam in the water that is against it, because the water will be still for quite a distance above it. You might, where that material would settle on sand of a certain character. If it did settle, it would have a tendency to make it more impermeable than it was before. But I do not think we could trust in this dam on checking off that flow of water by that means at all. I think the risk would be too great.

Senator DRYDEN. Does the great extent of this dammed-up water add anything to the weight or to the influence of this head of water seeking an outlet through this seepage?

Mr. WALLACE. The weight of the water is due to its head and not to its volume, except this, that over the entire bottom of this dam there is a downward pressure of, say, 38 or 40 pounds per square inch. That pressure is also horizontal, applied to this water flowing through the dam. That pressure exists over all this entire area, so that if half a mile away from here there was another vein of gravel underneath the indurated clay, and the inlet to that might be a mile above your dam or 2 miles, that weight would be there transmitted on that water to push it through under that clay, and you might find springs develop and waterways develop below your dam a great ways off even from these gorges, if there was any continuous strata that was water bearing that was connected with any of this water above the dam and any of this area in the swamps below. Springs might come up miles away from it, due to that cause, because that pressure is underneath the entire surface of your dam, no matter how many miles it may be in extent, due to the height of the water above the point upon which the water rests.

Senator DRYDEN. If it should be necessary in building across these gorges to make a provision such as you have referred to—running down these aprons until you strike a strong, sufficient foundation is that impracticable from an engineering standpoint ?

Mr. WALLACE. Well, in this particular case I would not undertake to do it—that is, if it was a work that I was doing for clients. No engineer would like to say that anything in an engineering way is impracticable. It is possible to close that off by a great many means, but you can not get at it to see it, and a great deal of it would have to be left to the discretion and judgment of the men that did it on the ground; and whether it could be done or not, or how long it would take or how effective it would be, are very uncertain quantities.

Senator ANKENY. I infer from that that the weight of that dam would increase the percolation. Is that right?

Mr. WALLACE. No, sir; I do not mean to say that the weight of the dam will increase the percolation.

Senator ANKENY. The water above would increase it?

Mr. WALLACE. The water behind it, in the lake that would be created by the dam, would increase the percolation, due to the head of the water.

Senator ANKENY. That is what all this means?

Mr. WALLACE. Yes, sir; that is what all this means. What I meant to say, further, is that, in my judgment, it would be a very unsafe thing to predicate this important work on a structure built at that point.

Senator ANKENY. Upon a plan open to these objections?
Mr. WALLACE. Yes, sir.
Senator DRYDEN. Have you found any other weak point in that
scheme for a dam except these two gorges?

Mr. WALLACE. I do not like the lock proposition that goes with it.

Senator SIMMONS. You said you made some borings after you went down there?

Mr. WALLACE. Yes, sir.
Senator SIMMONS. What was the greatest depth of your borings?

Mr. WALLACE. I think some of them were 200 feet. As I said before you came in the room, we abandoned the borings at one time, after we had commenced them and gotten down about 179 or 180 feet. Afterwards I went back again and explored that valley and made a great many other borings all through there.

Senator SIMMONS. Did you get through the indurated clay?
Mr. WALLACE. No, sir; I did not go down through that. All I
tried to do was to develop these gorges, because when I found (!?
depth that was below what I considered a practicable depth to take..
foundation to that, to my mind, settled that locality.

Senator SIMMONS. Were your borings altogether in the gorges?

Mr. WALLACE. No, sir. They were all over; some of them down here [indicating on map].

Senator SIMMONS. How deep did you go in the gorges?

Mr. WALLACE. My recollection is that before I left the deepest I found was about 200 feet.

Senator SIMMONS. How deep did you go through the indurated clay?

[ocr errors]
[ocr errors]
[ocr errors]


Mr. WALLACE. Whenever we struck the indurated clay and went into it 10 or 15 feet we stopped.

Senator SIMMONS. You did not prosecute your borings to the extent of finding what was the character of the material below the strata of indurated clay?

Mr. WALLACE. No, sir; because, to my mind, that was entirely unnecessary. Having found that there were deep gorges there (indicating on map], it looked like a waste of money to undertake any further experiments there. If that location had been selected for a dam and I had been instructed to build a dam on that location, I would not have stopped until I had gone clear through and into the rock and gotten through several stratifications, so that I could have found the geological sequence of the various stratifications.

Senator SIMMONS. Your 200 feet borings down those gulches there did not reach strata of rock or other hard substance?

Mr. WALLACE. No, sir.

Senator Simmons. Why did you stop at 200 feet? Why did you not go deeper down?

Mr. WALLACE. The reason was this: We were crowded for men, and we were crowded for material, and we had other questions that were of great importance that we must solve, and we needed every man and every machine that we had. As I abandoned that in my mind as a place for a dam when I got down that 200 feet and did not find any suitable material for a foundation, it was, to my mind, simply a waste of time to continue.

Senator SIMMONS. When you got down 200 feet and did not find any solid substance you reached the conclusion satisfactory to yourself that that was not a proper place for a dam?

Mr. WALLACE. Yes, sir.
Senator SIMMONS. When was it that you reached that conclusion?
Mr. WALLACE. That was, I think, in August, 1904.

Senator SIMMONS. Since that time you have been opposing this proposition to put a dam there?

Mr. WALLACE. No, sir. I went back again, at the request of the old Commission, and we took additional borings, because their theory was that at some place else across that valley we might find a continuous ridge of this indurated clay upon which this dam might be built, and it was on that chance that we continued our investigation.

Senator SIMMONS. Did you make borings elsewhere in the valley with a view to ascertaining whether conditions were different there?

Mr. WALLACE. Yes. That is the reason all these black borings were taken from here away above the dam [indicating on map?.

Senator MORGAN. Did you ever find that continuous ridge of impervious material?

Mr. WALLACE. No, sir; we did not.

While these borings were going on we had been boring at Bohio and had gotten down 167 feet at Bohio, in a gorge there. We had followed that gorge


up to Gamboa, and we found it ran out at Gamboa and the rock came up to sea level. My natural supposition was that, going down to 200 feet here [indicating on map] and 167 feet at Bohio and finding that all the way up the valley the rock pitched and would be found at some very great depth here [indicating on map], but certainly under 250 or 300 feet at this point [indicating on map], that we certainly would not find that it was at a

[ocr errors][ocr errors]

higher elevation lower down the gorge than we found at Bohio, because the evidence all seems to show that this gorge had been formed by the flow of water, and that water must, of course, have been running downhill toward the sea.

Senator SIMMONS. It was in August, 1904, that you completed these borings in the gulch?

Mr. WALLACE. No, sir; it was August, 1904, that I found out that one of these gorges existed; but we took a great many additional borings after that.

Senator SIMMONS. When was it that you completed the borings as to those gorges and made up your mind that that site would not do?

Mr. WALLACE. That was in August, 1904.
Senator SIMMONS. That is what I understood you to say.

Mr. WALLACE. That was with this reservation, that if we did find

Senator SIMMONS. I am talking about this site.

Mr. WALLACE. But I mean to say this: That we did not abandon that entirely, but it was with the reservation, of course, that if we did find a barrier of this indurated clay extending clear across the valley, and then found that that was down to the bed rock, and that thero was no water-bearing strata under it, we might go back to that and put a dam there.

Senator SIMMONS. But you did find upon this identical situs these gorges and you did bore down 200 feet?

Mr. WALLACE. Yes, sir.

Senator SIMMONS. And you came to the conclusion, as a result of those borings, that this precise place would not do?

Mr. WALLACE. That is correct.

Senator SIMMONS. What I want to ask you is this: Is there any report of your to the Commission or any written statement of yours to the Commission, made at that time, of the conclusion you had reached in this regard?

Mr. WALLACE. Yes, sir; that is contained in letters addressed to Admiral Walker, the chairman of the Commission, and it was also covered by verbal reports that I made to the Commission when they were on the Isthmus in that month.

Senator SIMMONS. You wrote letters to the chairman of the Commission?

Mr. WALLACE. Yes, sir.

Senator SIMMONS. Giving your opinion as you have stated it to be here?

Mr. WALLACE. Yes, sir.
Senator SIMMONS. In August, or about August, 1904 ?
Mr. WALLACE. Yes, sir; 1904.

Senator SIMMONS. After that opinion was given by you did you make any more borings at this particular place or in the line of the dam at that particular place!

Mr. WALLACE. In the general vicinity. That matter was referred to Mr. Nichols, and we let him use his judgment as to where he should make his borings after that time. In other words, the consideration of the whole problem of physical research from Mindi clear up to Bohio was left in the hands of Mr. Nichols to investigate as he saw fit,

[ocr errors]
« PreviousContinue »