Lesson 2/Learning Event 7
Width of Initial Cuts. The total width of initial cut will be determined by working space requirements
of loading and hauling equipment. For all cuts this width will be the same as the width desired at the
initial face. In the normal method of loading out blastrock, i.e., with a crawler shovel or front loader,
this width will range upwards from 40 feet (12 meters).
Charging Initial Cuts
The holes in initial cuts will normally be located with the same objective as in normal production
blasting. This is to obtain good fragmentation with little displacement. However, in the case of cuts
below grade (ramp, V-, and pyramid cuts), it may be advantageous to load heavy with the objective of
removing as much material as possible from the cut with the blast. This practice may be limited by such
factors as the proximity of personnel and structures to the area and the damage which may result from
the shock and flyrock produced by blasting. A well designed blast results in good fragmentation, good
displacement, and minimum violence.
Backfilling
All cuts described in the preceding paragraphs are intended to break the rock to a depth of from 1 to 3
feet (0.3 to 0.9 meter) below the final grade. Backfilling will be necessary to bring the surface up to a
smooth, usable grade at the desired elevation. This must be accomplished to a certain extent with rock
broken in the blast. However, a certain amount of usable fill with grading and compacting equipment
may also be necessary to complete the job. Backfilling is not required when a suitable working floor
can be developed by controlled blasting or by use of an existing bedding or fracture surface at the level
of the quarry floor.
Excavating with Draglines
Draglines are best used to excavate loose materials below the track level of the machine. It is the most
practical piece of military equipment for under water digging and is well adapted to submerged gravel
pit operations. Typical dragline jobs are recovering sand, gravel, or coral from streambeds, lake
bottoms, lagoons, and beaches. The primary use of draglines is to stockpile material for other loading
equipment or to load hoppers.
Radio, wire, and special signalling devices for warning before blasting are essential to safe, efficient
operations. Radios in the immediate vicinity should be turned off during loading and blasting of
operations.
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