Page 464 - Moving the Earth_ The Workbook of Excavation

BLASTING AND TUNNELING

9.64 THE WORK

The perpetual problem in tunnel haulage, which becomes more acute as size decreases, is
bypassing the empty cars (or trucks) going to the face around the full ones coming away from it.
Empty cars may be switched to the side; or if they are small, lifted or pushed off the track by hand,
where there is space for only one track. Larger ones may be handled by a cherry picker. In either
case the spotting arrangement shown in Fig. 9.53 may be used.
The locomotive pulls a string of empties into the heading and stops to let the cherry picker take
up the rearmost car and set it aside. The locomotive then backs far enough that the car can be
replaced on the track in front of it; then pushes that car up the loader. While it is being loaded, it
backs so that another car can be picked off.
When the car is loaded, the locomotive couples to it and backs past the cherry picker, which
places the empty in front of it to be pushed to the face. While it is loaded, the rear empty is again
set aside, to be pushed in on the next cycle. When all the cars are filled in this manner, the loco-
motive pulls them to the shaft.
In a tunnel of sufficient height, a movable framework called a Grasshopper, Fig. 9.54, can be
used. This allows the empty cars to be moved over the loaded ones, and can be pulled up to the
face by the loader.
A conveyor belt may be set up so that a full train of cars can be backed under it, and loaded
one by one from the front to back.
Conveyor belts can also be set up to haul from the face to the shaft. No switching arrangements
are required, but this unit cannot be used readily to bring supplies from the shaft to the face; con-
siderable work is involved in dismantling or protecting it for a blast, and there is constant work
adding sections to keep it in touch with the digging.
Diesel-powered trucks are used for large tunnels. They carry much bigger loads than mine
cars, and if sufficient width is available to make passing possible, they get past each other with
fewer complications than rail-mounted carriers. The shuttle types, such as the Dumptor, which are

FIGURE 9.53 Portable switch.

FIGURE 9.54 Grasshopper overhead switch.