Page 462 - Moving the Earth_ The Workbook of Excavation

BLASTING AND TUNNELING

9.62 THE WORK

1
Slick sheets should be used in connection with hand loading. These are thin steel plate, ⁄ 4 or
5
⁄ 16 inch, in pieces about 4 6 feet, with holes punched for convenience in picking up for moving.
They are laid to cover the tunnel floor for 10 to 25 feet back from the face before each shot. Large
rocks are picked up and thrown into the cars individually, while the finer material is dug by shovels
that slide easily along the metal surface.
Mechanical loaders include full-revolving shovels with short booms and proportionately larger
buckets, that move on either crawlers or rails.
Special tunnel-mucking machines are available in large variety. Most are rail-mounted, although
crawlers are gaining in popularity. The bucket can be swung from side to side to reach the full
floor area, and is filled by pushing into the pile.
It is then lifted, in some models over the machine to discharge into a car or conveyor belt behind;
in others it loads a built-in conveyor that discharges to the rear. In either case, the car may be coupled
to the mucker so that it is always in loading position.

BORING

A tunnel may be cut to full size in a single operation by boring with a tunneling machine, sometimes
called a mole. These machines are described in Chap. 20. See Fig. 9.51.
A tunnel borer grinds, chips, or digs its way through formations, by rotary or oscillating motion
of cutter teeth, and deposits the muck onto a conveyor belt for discharge into haulers at the rear.

FIGURE 9.51 Bored tunnel face.