228

THE COLLIERY GUARDIAN.

August 2, 1918.

sufficient thickness to permit of a large pressure being
applied, the method adopted is somewhat modified,
in that, before direct injection takes place, one or
more release boreholes are drilled through the walls
of the shaft well back to intercept the fissure at a
considerable distance inside the rock. These holes
allow the water to escape and relieve the side of the
shaft of the pressure necessary for cementation. A
thick cement mixture is then introduced through the
weep pipes, which seals the fissure in the immediate
vicinity of the shaft; and when set, the final injection
takes place through the release holes mentioned. By
systematically dealing with all water in shafts in this
manner it is quite possible to get a perfectly dry shaft.

Sealing Open Fissures.

Generally speaking, the method adopted in dealing
with open fissures through which any considerable
quantity of water is flowing is to drill two or more

i
5? I

Section on W—E.

Fig. 2.—Boreholes for Cementation at Daggafontein No. 2
Vertical Shaft. Holes 1-12, 8° out ; holes 13 and 14,2J° out.

as fast as it is injected. If, however, the water can
find an easier escape through these release holes it
will take that course, and thus permit of the following
treatment: —

The flow of water from the mouth of the fissure
is first of all restricted by careful wedging. Thick
cement, with an addition of sawdust when necessary,
is then injected through one of the drill holes, and
settlement begins on the support offered by the wooden
wedges driven into the open end of the fissure. When
this cement has set in the area between the release

Section on A—B.

N

W ;

SYCNKTV

/,«fo

*

.to

J

\

Fig. 3.—Treatment Plan at Brakpan No. 3 Circular
Shaft. All holes 8° out.



gallons of water per hour. This was treated in the
manner described, and within eight hours the water
was effectively sealed off. A modification of this class
of work has been successfully carried out at the Geduld
Proprietary Mines. In this case, however, the fissures
were of a very wide nature, carrying a large quan-
tity of water, and it was deemed advisable as a pre-
liminary to build a cylindrical concrete dam at the
point where these fissures intercepted the drive. This
dam on completion, was found to leak badly, and at
this stage the cementation pump was brought into use,

Fig. 4.

(Water pressure 1,0001b. per sq. in.).

0.
»’

Fig. 6.—Section of Concrete Tubbing in a
Circular Shaft.

Showing fissures, weep pipes, release holes, and
general arrangement for cementation.





Fig. 5.—30 W Drive, E.R.P. Mines. Brick Dam, with Double Filling behind, and
Arrangement of Holes for Cementation.

release Rules, at some distance back from the mouth
of the fissure, for the purpose of allowing the escape
of the water during the time of sealing the opening
of the crevice. Unless some system like this be used,
the force of the water will wash out the cement grout

holes and the fissure opening, the final injection takes
place directly through the release holes.

As an example of this class of work, it might be
mentioned that in the 28 West Drive, Angelo Deep,
a certain fissure allowed an escape of about 3,000

and the dam rendered water-tight. Practically speak-
ing, this operation is the same as that described above
in connection with shaft lining.

Damming Back Water in the Vicinity of Broken Ground.

The process adopted for sealing back water leaking
through the cracks and crevices of broken ground is
similar to that adopted for sealing open fissures,
though at times it calls for special care, as the weak
nature of the rock tends to burst it out when sub-
jected to pressure while injecting.

Rendering Underground Dams Watertight.

However carefully an underground dam is con-
structed, a great deal of leakage takes place, more
especially when the water is under considerable pres-
sure. In this connection cementation can be very
successfully used for making the dam water-tight by
injecting cement through holes suitably drilled into
the construction. A good illustration of this work is
afforded by the large control dam built in the 26 Cross-
cut at the East Rand Proprietary Mines. This dam
is 30 ft. thick, and has an opening sufficient to permit