Page 503 - Moving the Earth_ The Workbook of Excavation

PIT OPERATION

PIT OPERATION 10.9

FIGURE 10.8 Wheel and shovel team.

FIGURE 10.9 Overburden removed with drag scraper.

Double Casting. If a space is required which is wider than that which can be stripped by avail-
able shovel and dragline equipment, and the spoil is too coarse for scrapers, a shovel may be used
to swing the spoil out onto the pit floor, and a dragline to pile it on the bank. The illustration in
Fig. 10.10 is of a quarry requiring a wide working area below the face.
For best results, the two machines must work together as, if the backhoe is allowed to build a
substantial windrow, the dragline will need a longer reach to get to its far edge.
A dragline may also be operated on the previous spoil bank, to take off the top of the pile being
built by a shovel and thereby to increase its disposal capacity.
The extra expense of double casting limits its use to special conditions.
Deep Stripping. Strip operations often run into areas where depth of overburden is too great for
efficient sidecasting with available equipment. This may be handled by two trips of a shovel, by
a shovel and wheel, or by a shovel and dragline.
Two trips with excavators may be made for drilling and blasting convenience rather than to
make up for a lack of reach. Taking a high bank in two levels may result in worthwhile savings.
The strata in the upper and lower lifts may differ in quality so that different drilling and blast-
ing techniques are used. In some cases one will require blasting whereas the other will not.