Page 457 - Moving the Earth_ The Workbook of Excavation

BLASTING AND TUNNELING

BLASTING AND TUNNELING 9.57

FIGURE 9.46 Raise and glory hole shaft excavation.

A continuous lining or lagging is used in soil that might squeeze between ribs or timbers, or in
rock that scales or breaks off so that falling pieces would endanger workers. Unlagged walls may
often be kept intact by spraying with shotcrete or a bituminous mixture.

Drainage. Most shafts are wet. If there is only a little water, it can be bailed into the bucket and
hoisted with the muck. More often it is removed by a pump with a discharge line reaching to the
surface or, if the height is great, to one or more pumps that help push the water out of the shaft.
All pumps used in deep shaft work should be able to develop very high discharge pressures, so
that a good lift can be obtained between boosters.
If water conditions are severe, the area may be predrained by sinking 4- to 12-inch holes with rotary
drills, and pumping from them. Depth is too great for ordinary well point work from the surface, but
in flowing ground well points may be sunk from the shaft bottom or sides, and the water rehandled by
the regular pumps.
A deep, wet shaft should have gutters and sumps at intervals, to catch water running down the
sides. Pumping to the top from intermediate points may be more efficient than allowing it to get
down to the bottom and raising it from there.
Shaft Sinking Machines. A large and increasing percentage of new shafts are cut in a single or
dual operation by gigantic drills, described in Chap. 20.

HEADINGS

A heading is a digging face and its work area. Conventional tunnel driving is discussed here.
Tunneling machines (borers or moles) are described in Chap. 20.
When the shaft has reached the level of the proposed tunnel floor, two headings are started, one in
each direction along the line of the tunnel. In addition, the foot of the shaft may be greatly expanded
for storage and maneuver space, and one or more rooms may be built to house compressors, pumps,
and other plant equipment.