Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

ROCK EXCAVATION.

125. The sides of rock excavation are sometimes cut to a small slope, as one fourth or one fifth horizontal to one vertical, and sometimes cut quite perpendicularly. The earth, when it occurs, which covers the rock, is first taken out at the proper slope; a berm of one or two feet being left between the foot of the earth and the crest of the rock.

126. Rock is taken out one or two feet below grade, as well as earth, to allow the introduction of the necessary ballast.

BLASTING AND QUARRYING.

127. The most common mode of removing rock is by blasting; for this holes are drilled by steel-edged jumpers, worked either by hand or by steam. The first object in cutting a passage through rock, is to open a working face, so as to get the necessary lines of least resistance, (this line is that by which the powder finds the least opposition to a vent at right angles to the length of the drill); these lines should, if possible, be at right angles to the beds of stratification; the holes should be drilled parallel to the seams of the rock, as the powder will then lift off the strata. In working a vertical face, it may be best to blast out the lower part first, and so undermine the overhanging mass.

128. The amount of powder in different charges to produce proportional results should be as the cube of the line of least resistance; for example:—

2³ is to 4 oz. as 3³ is 13½ oz.,

or

8 to 4 as 27 to 13½;

and generally,