380 REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL.


earth barriers remain that would answer the same purpose, and then pump out the intermediate spaces. As far as the excavating of rock under water is concerned, there is one process that has not been touched upon iij any of these reports, but I think Mr. Bunau-Varilla referred to it, and that was the breaking up of the rock by what is called "chisel work."
 Mr. HUNTER. You mean the Lobnitz system?
 Mr. WALLACE. I do not know what you call it.
 Mr. HUNTER. You, perhaps, need not enlarge upon that. We have discussed that at great length here. It is a process with which Mr. Quellennec and I both happen to be extremely familiar.
 Mr. WALLACE. I simply wanted to remark that 1 worked that same system for five years over thirty years ago in the Mississippi River, with the hardest possible limestone rock, and we did it with slender chisels, probably 16 to 18 feet long, and weighing only a few tons. Still we had remarkable success with it. I only wanted to touch upon it as a possibility.
 Mr. HUNTER. I am doing it in quite another part of the world on a very large scale, and we have had that very much before us. Do you not think it would be a little more prudent, in contemplating the construction of a great canal of this charater, for this Board to regard that the whole of this excavation in the Culebra cut may be removed in the dryv
 Mr. WALLACE. I think it would be more prudent; yes.
 Mr. HUNTER. And below whatever elevation may be necessary to allow Some safe and conservative condition?
 Mr. WALLACE. I think it would, Mr. Hunter.
 Mr. HUNTER. What do you think that elevation would be?
 Mr. WALLACE. Down to 10 feet above sea level the cut should drain itself by gravity. What it would cost per cubic yard to pump the water from the excavation below that elevation I do not know.
 Mr. HUNTER. How are we to find out? What is your view about it?
 Mr. WALLACE. I will give you some experience that may help as data. I have seen pumped out a cofferdam containing about 10 acres of surface-I have not figured this out, because I did not expect to raise this question-with an average depth of 10 feet, in twenty-four hours. This was over twenty-five or thirty years ago, and the only factor that I do not bear in mind now was ,the number of centrifugal pumps we used and their size.
 The CHAIRMAN. Do you remember the cost?
 Mr. WALLACE. I do not think the cost exceeded $100 for that-area. That. is just simply a rough estimate, but I do not remember the size of the pumps nor how many we had. I know we had our pumps all at the lower end of the dam.
 The CHAIRMAN. You had the pumps on hand? You did not have to buy them ?
 Mr. WALLACE. We had the pumps on hand; yes. I mean $100 was simply the cost of the coal and the wages.
 Of course the cost at Culebra would depend on the way the cut was- drained-on the watershed that would be tributary to your cut when you got down to the greatest depth, and also on the amount of rainfall, and on a, great many elements that are very difficult to determine. Of course the probabilities are that anyone doing that work would do everyting possible to crowd it during the drier months.
 The CHAIRMAN. Have you thought of a level at which you would almost certainly have to pump?
 Mr. WALLACE. I should judge that that cut could be properly drained down to about, possibly, 10 feet above sea level.
 Mr. WELCKER. Mr. Chairman, the Committee on Unit Prices has adopted the figure of 45 cents per cubic yard, but it is a matter of great uncertainty. We have put that figure on it because it was necessary to do so; but no man in the world knows how much it will cost..
 Mr. HUNTER. I was very anxious to get Mr. Wallace's opinion upon that. The Committee on Unit Prices put it at 45 cents.


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