A GREAT ENGINEERING OPERATION.

Temuka Leader, Issue 1404, 13 October 1885, Page 3

A GREAT ENGINEERING OPERATION.

A cablegram received last Sunday jays The operations which have been carried on for some time past by the Marine Department, with a view to clearing East River Channel, were successful)finished to-day, when no less than nine acres of reef, in what is known as Hell Gate, were successfully removed by means of dynamite. We find the following description of the work in a contemporary : The preparations for blowing up Flood Rock, a largo and dangerous reef in the track of vessels entering New York harbour through Hell Gate, are beiugactively pushed forward, and it is expecied that the mine will be ready to be fired early in the coming autumn. It will be remembered that the formidable reef known as Eallott’s Point, also in Hell Gate, was blown up about ten years ago, when fio,ooolbs of dynamite were used. The present undertaking is on a much larger scale. The section of took then demolished was only three and a-half acres in extent; but this time nine acres of rock ar* to be blown up, and nearly SOO.OOOlbsof dynamite, or rather of “rackstock, ’’ a newer and more powerful explosive, will be used. The work on Flood Rock was commenced before the Hallett’s Point was destroyed, and has been going on at intervals ever since, as the money was voted by Congress. One great difficnlty experienced has been to keep water out of the mine, and of late three pumps have been almost constantly at work pumping out the water which percolates from the river above. In all, 21,670 ft of galleries have been cut through the rock in various directions, and 13,700 holes, Sin in diameter, and of an average length of 9ft, have been bored upward from the galleries. This work has been done by a drilling machine driven by compressed air. Through the shaft which leads down to the workings 80,160 cubic yards of rock have been carried up. The bottom of the main shaft is 60ft below the level of the river, and radiating from this are the galleries, which run for hundreds of feet under the rocky ledge. The height of these galleries varies from sft to 12ft, and along each runs a railroad track, used for carrying away the rock as the galleries are extended. In some place* the water comes in so freely as considerable anxiety to the engineers in charge of the work, and this is particularly the case with about an acre of galleries at the north end of the ledge. To guard as much as possible, however, from a sudden inrush of water, this part has been shat off from the other excavations by a heavy water-tight door. It is expected that by the end of the present month the work of loading the mine will be begun. The explosive to be used consists of two ingredients, which are quite harmless when not brought together. They are, when combined, to be packed in copper cylinders 2Jin diameter and 2ft long, each holding about bix ponds of the explosives. In addition to the 225,0001bs of the “rackarock.” about 75,0001bs of dynamite will be used. The delicate operation of packing the compound into the cylinders is to be performed by special experts, and other picked men are to place the cylinders in the holes prepared for them, aod to connect them with the exploding wires. When the cylinders are all in, and the wires laid, the mine will bo flooded with water, and a favorable moment awaited for firing it. It is estimated that the whole work will cost about 1,000,000d015, and it is confidently expected that the result of this gigantic explosion will be to completely clear the track through Hell Gate, and to do sway with all danger to navigation.