472 



HELL-GATE, IMPROVEMENTS AT. 



1874, to Jan. 20, 1875, and the depth of water were excavated, till 35 tunnels and 10 galleries 

 was increased to 26 feet at low water. The were constructed, having an aggregate length 

 rock within the 26-foot curve measured 235 of 7,426 feet. The tunnels were from 17 to 22 

 feet in length by 115 feet of maximum width. 

 Two hundred and sixty-two holes were drilled 

 to an aggregate depth of 2,130*4 feet, 65 drill- 

 blasts and 16 surface-blasts were made, and 

 16,792 pounds of nitro - glycerin and 38 



pounds of dynamite were used. 

 Ballet's Reef. For the removal of Hallet's 



feet high and from 9 to 12| feet wide at the 

 shaft, and tapered off in both dimensions as 

 they went out; and the galleries were from 12 

 feet high by 9 feet wide down to smaller di- 

 mensions. 



The work of excavation was begun in Oc- 

 tober, 1869, and terminated in .June, 1875. 



iiniiiia Atrci* -L' ui tiic iciuuvtu. \Ji xAaiicu o twuci, O.<JVF^, a-uu. uci Luiuutcu. m > uiae, J.O|J, 



Point Reef it was determined to employ a Deducting the time lost by suspension of work 

 process of undermining the rock by tunnels due to the exhaustion of current appropria- 

 and galleries, from which mines should be tions, the actual period consumed in this work 

 exploded to break up the whole mass of the was four years and four months. The ap- 

 rock at once. The reef in question was in the propriations were, under the law, devoted to 

 shape of a semi-ellipse, extending 720 feet along many reefs in the East River and Hell-Gate 

 the shore, and 300 feet in breadth into the besides the one at Hallet's Point ; the result 

 channel; and the cubic contents necessary to being that the work was rarely prosecuted 



in full force at the 

 latter place. As soon 

 as the excavation was 

 finished, the work of. 

 drilling holes in the 

 roof and piers, to be 

 charged with explo- 

 sives, was begun. 

 At the completion, 

 March 25, 1876, there 

 had been drilled in 

 the roof 5,375 three- 

 inch, in the piers 

 1,080 three-inch and 

 286 two-inch holes; 

 the total length of 

 holes drilled being 

 56,548 feet of three- 

 inch and 1,897 feet of 

 two-inch holes. The 

 proximity of the reef 

 to habitations at As- 

 toria, Ward's Island, 

 and Blackwell's Isl- 

 and, made it neces- 

 sary to devise a sys- 

 tem of explosion 

 which, effecting the 

 work of demolition, 

 would do no damage 

 to life and property. 

 It was evident, if to 

 each charge its full 



HALLET'S POINT SECTION THROUGH TUNNEL NO. 7. Capacity f USfiill 



work m breaking up 



be removed, in order to secure a depth of 26 the rock were assigned, regard being likewise 

 feet at mean low water, amounted to 53,971 had to the superincumbent weight of water, no 

 cubic yards. The reef was dangerous, not only external effect of moment would be perceived 

 in itself, but al?o on account of the eddies to in the atmosphere. It was also evident that 

 which the tidal currents gave rise on either the magnitude of the rock-wave would depend 



side of it. Operations were begun herein Al - """ "' 



July, 1869, for the construction of a coffer- 

 dam between high and low water marks; and 

 in the following October the excavation of a 

 shaft, conforming in shape to that of the dam, 

 and 32 feet in depth, was begun. Thence tun- 

 nels radiating through the rock, with trans- 



verse galleries, 25 feet apart, to connect them, 



greatly upon the quantity contained in indi- 

 vidual charges ; that is, if 80 pounds were re- 

 quired for the individual charge, the vibration 

 of the rock would be much greater than if 

 these charges did not exceed 20 pounds, 

 was known that 80-pound charges of nitro- 

 glycerin, fired in numbers of 12 to 20, did not 

 cause a destructive wave. Again, the reef, 



