Читать книгу Tri-nitro-glycerine, as Applied in the Hoosac Tunnel, Submarine Blasting, etc., etc., etc онлайн

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The two drill carriages employed are larger than those at East End, and are intended to carry five drills each—in all, ten drills working at the breast of the heading. Assuming, as we may safely, that the rate of progress is proportional to the number of drills employed, ten drills would advance 100 feet per month; and with full power provided and further experience to be acquired by the workmen, this and even greater average rates of monthly progress can be made and maintained.

These headings are run at top, i.e., above the excavations hereafter to be made, and of such height, and top outline as to correspond with the roof of the completed tunnel.

Amounts of progress upon this section of the work during present and preceding year are exhibited in the following comparative table:—

West Shaft Heading and Adit. Enlargement. Section. Linear Feet. Cubic Yards. Linear Feet. Cubic Yards. Year Ending November 1, 1867 543 2349 161 2100 November 1, 1868 1280 4696 82 488

The limited employment of Nitro-Glycerin made previous to August 1st, had been directed to excavations of enlargement, which very nearly resemble open cut work. The experience of the two months, August and September, is all we have that throws direct light upon its value in mining operations, using this phrase in its more limited sense, as applied to advance of heading only. The varying hardness and tenacity of rock and other attendant conditions, make material variations in the progress of separate days or weeks, even in the same drift and with the same means and appliances of working.