Page 403 - Moving the Earth_ The Workbook of Excavation

BLASTING AND TUNNELING

BLASTING AND TUNNELING 9.3

FIGURE 9.2 Drilling near a high face.

Highway Cuts. Rock cuts for highways may be of the through type as in Fig. 9.3(A), and the
sidehill (B). Material from a sidehill cut may be thrown down to make a fill, as in (C).
The area to be cut should first be cleared and stripped of loose soil, and preferably of rotten
rock. This may be done with dozers, scrapers, or shovels, depending on the conditions and the
equipment available.
If the rock is soft, its upper surface may be loosened with rippers and removed, along with any
dirt pockets it may contain. If it is hard and irregular, extensive cleaning by hand and with small
equipment may be necessary. It is desirable to remove all loose dirt, particularly if the rock is to
be used as crusher aggregate for road topping.
When water and disposal areas are available, hydraulic cleaning with contractors’ pumps and
fire hose or with special equipment may be used.
If cleaning is not practical over the whole area, the spots to be drilled can be cleaned individually.
The top layer may then be drilled, shot, and removed for fill, and any clean rock required can be
obtained from lower levels.
If the cut is 20 feet or less in depth, it may be taken in a single layer, but depths of 12 to 15 feet
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are generally considered most satisfactory for track drills, and digging by 1- to 2 ⁄ 2 -yard shovels or
medium-large front loaders.
In a through cut, the full width is used as a face to provide maximum space for machinery. On
a sidehill, the same technique or one or more bench faces parallel with the centerline may be used.
Degree of fragmentation required is determined largely by the depth of fill layers where the
spoil is used.

Mining and Quarrying. Pit operations are largely conducted to obtain certain classes of rock or
earth. The general aspects of this work will be discussed in the next chapter.