EXCAVATION OF SUBAQUEOUS ROCKS 



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per cylinder of smaller diameter than the drill hole but of sufficient 

 length to admit the entire cartridge. At the upper end is attached 

 a piece of iron gas pipe long enough to extend well above the surface 

 of the water. The copper cylinder is slotted on one side through- 

 out its length to permit the insertion of the cartridge, with its 

 exploding wires fastened to the upper end. When the cartridge 

 with its wires has been passed iixto the cylinder, the latter is inserted 

 in the drill hole, and a long pole is passed down through the gas 

 pipe forming the extension of the cylinder. The whole pipe is 

 then withdrawn, the pole being used to prevent the cartridge fro 

 coming with the cylinder. As soon as the charging apparatus hi 

 been entirely removed, the cartridge is exploded. 



Costs. Concerning the cost of excavation of rock under water ' 

 by blasting, Mr. T. Jenkins Hains, while in charge of the New 

 York office of the Nicaragua Canal Commission, collected valuable 

 data from the report of the Chief Engineer of the II. S. Army con-, 

 coming the cost of dredging rock in the year 1897, in different parts of- 

 the country. He gives the following examples of the cost of rock 

 excavation under water: 



Cocheco River, N. H ledge 1300 cu.yds. 



Bronx River, X. Y 



Sullivan Falls 



Kennebec River 



Sassanoa River 



Moosabu, Me 



Boston Harbor 



From these examples it can be deduced that, broadly speaking, 

 the cost of rock excavation under water is directly proportional to 

 the depth of the ledge and inversely proportional to the quantity. 

 But a more correct idea of the cost of removing subaqueous rocks 

 by blasting and dredging can be obtained from the following examples 

 taken from Engineering News, Vol. LVL These show the results 

 obtained by two different contractors in removing ledges of calcare- 

 ous rocks, in deepening the channel of the Detroit River, the con- 

 tractors working on two different sections. 



The contractors for Section 2, Messrs. G. H. Breymann & 

 Bro. of Toledo, O., agreed to excavate the rock at the following 

 prices: $3.25 per cu.yd. bank measurement, for all the material 

 above the 22-ft. grade, and $1.625 per on .yd. for all material removed 

 between the 22- and 24-ft. grades. The contractor's plant consisted 



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