Reports on the Philadelphia International Exhibition of 1876.

Date:
1877-1878
Catalogue details

Licence: Public Domain Mark

Credit: Reports on the Philadelphia International Exhibition of 1876. Source: Wellcome Collection.

    374/446 page 276
    * 270 Commencement of work. Plan of operations. Extent of tunnellint is to widen and straighten it by securing a minimum depth of 26 feet of water over the reef. The work was commenced in July 1869 by building a coffer dam between high and low water marks. In October following the excavation of the shaft was begun. From the bottom of the shaft 10 tunnels were driven under the river in radial lines and were extended until a deptb of water upon the reef of 26 feet at low tide was reached, tlie roof of the excavation being kept nearly parallel to the bed of the river and about 10 feet below it. The main tunnels are about 14 feet in width, varying from 10 to 20 feet in height and averaging about 270 feet in length. They are connected with each other at intervals of 30 feet by means of cross tunnels or galleries of about the same height and width. Between the tunnels and galleries large columns of solid rock were left to support the roof of the excavation or bed of the river; these large columns were afterwards cut through by other tunnels and galleries, and finally 173 piers or columns were formed, averaging about 10 feet each in thickness. The entire roof thus undermined covered an area of three acres. The aggregate length of tunnels and galleries driven under the bed of the river was 7,4-5 feet. From the excavation about 47,460 cubic yards of rock were removed by drilling and blasting, an operation which required 208,174 lineal feet of drill-holes, of which 90,107 feet were drilled by hand and 118,067 feet by various kinds of machine drills, viz., The Burleigh, Diamond, Rand, Win- chester, Wood, Ingersoll, and Waring drills, worked by compressed air. Modus operandi. The usual method of driving a tunnel or gallery was as follows : the face of the rock was pierced obliquely with as many drill-holes from 3 to 4 feet in depth as were deemed necessary; the charges were then prepared by placing the explosive material in water-tight paper cartridges from 8 to 12 inches long and containing from 8 to 12 ounces of explosive mixture; into each of these cartridges a copper cap containing mercury fulminate fastened to the end of a piece of safety-fuse, generally about 5 feet in length, was inserted. The cartridge was then pushed to the bottom of the hole, which was filled with water ; the ends of the fuses hanging from the drill-holes were then ignited. In the preliminary operation of forming the tunnels and galleries the following quantities of explosives were used :— Quantity of explosives used Blasting powder Nitro-Glycerine Giant powder Mica powder Vulcan powder Rend Rock 24,431 pounds 26,471 „ 1,932 „ 600 4,017 „ 1,500 „ Model. Similar works at the Flood Rock. Float or scow. In exploding these compounds 63,756 exploders and 331,516 feet of Bick- ford's safety-fuse were used. In all about 75.000 blasts were fired. A good model showing the tunnels and galleries and the pillars left to support the roof was sent to the Exhibition. When I visited the work at the beginning of August last holes had already been drilled in the pillars and roof to receive the explosives for the final explosion. These were intended to be charged with nitro-glycerine cartridges to be connected by wires with a battery to be placed at sufficient distance. It was intended before making the discharge to fill all the tunnels and galleries with water. The explosion took place a few weeks after I left. To complete the work the debris will have to be removed. It will be interesting to learn, when the work has been completed, what has been the total cost to compare with the probable cost of reducing the shoal by the more usual method of submarine blasting. The excavation of another reef in the channel, the Flood Rock, has already been commenced upon the same principle as applied at Hallett's Point. While on this subject, it may be useful here to mention a machine used in the United States in removing reefs and rocks under water by blasting from the surface, and which is described as follows. Steam Drilling Scow. The machine consists of two parts, a large float or scow having a well-hole in it of a diameter of 32 feet. It is built very heavy and strong, and is provided with an overhang or guard around it faced with iron, and has proved itself up to this time capable of withstanding violent collisions with other vessels.
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