1020

THE COLLIERY GUARDIAN.

November 15, 1918.

as well as nearly ending the proceedings in dire
failure. In the ordinary course of sinking, the bottom
of the crib is never seen from the time it leaves the
surface until it reaches the rock head, as it is con-
tinually travelling hi advance of the sinkers. The
distance that the crib is in advance is greatest at the
commencement of operations, and in the soft mud it
reached as much as 4 fathoms in advance. As the
sinking proceeds, however, the distance gradually
diminishes, and at a depth of 60 ft. the sinkers were
able to get down to within 2 or 3 ft. of the bottom
of the crib.

The Disastrous Attempt.—As a result of the crib
coming to a standstill the position became desperate,
and as in such condition of affairs warranted a
desperate remedy being attempted, and it was this
alone that induced the author to sink below the crib
in order to make certain that it had freedom to sink.
On proceeding, it was found that the crib had passed
through the running sand and had entered into tough
mud or soft blue clay. The section sunk through so
far was composed of—

Soil ............................... 1	ft.

Yellow clay ...	...	...	...	4	,,

Mud with boulders	...	...	...	50	,,

Sand and gravel	...	...	...	22	,,

Clean sharp sand...........	... 10 ,,

—a total of 87 ft.

The sand having been cleaned out to the pit bottom,
sinking was continued below the bottom of the crib,
in order to relieve it. A very few inches of clearance
might have been sufficient to demonstrate that the
crib and brickwork would sink no further, but some-

Fig. 2.—Sectional Elevation of Sinking Crib.

thing like 18 in. to 24 in. below the crib had been
sunk when disaster occurred. The mud which was
being sunk through was tough all over the pit bottom
except at one point on the perimeter. Here it was
very soft, and latterly burst in, bringing with it the
sand and mud above in such quantities that the shaft
was more than half filled within the space of a few
minutes. Luckily no lives were lost, as precautions
had been taken to have four safety ladders hanging
down the sides of the shaft, by means of which the
sinkers escaped. Not too soon, however, as they expe-
rienced the greatest difficulty in claiming as fast as
the sand, etc., was rising inside the shaft. As soon
as the sinkers were got out, a close inspection revealed
the fact that the inrush had extended right from the
surface, leaving a hole 3 ft. by 2 ft. at the surface
and down behind the back of the brickwork. (Fig. 4.)

Plugging the Breach.—The problem now which
required solution was how to plug this opening and
stop the inrush. Many possible solutions were ad-
vanced, and even tried, but without success, and it
will suffice to give here a brief description of the last
two of these fruitless attempts.

(1)	Bales of compressed straw were procured and
stuffed into the hole at the surface, and these firmly
pressed down until the hole was completely filled.
Sinking operations were again resumed and the sand
filled out until the bottom of the crib had again been
reached. It was then found that the straw at the
bottom of the crib effectually plugged the hole from
where the inrush had taken place. This plan might
have succeeded but for unfortunate delays which
allowed the straw to rot before full advantage of it
could be taken. This decomposition of the straw gave
rise to the presence of a pungent odour of gases,
probably ammonia or its compounds, in the pit bottom,
so strong as to make work impossible. The rotting
process continued until the straw gave way and
another inrush of sand and mud occurred, again
filling more than half the depth of the shaft.

(2)	The next attempt, after considerable delay, was
to try and stop the gap by means of wood piles.
These were procured and driven down all round the
inside of the crib until every possible escape for the
sand seemed barred. Heavy permanent rails bent to
the circle of the piles were then fitted inside of them
with a view to preventing their collapse. As sinking
proceeded a series of rail rings 3 ft. apart were put
in, each pile, where necessary, being wedged tight
against the ring. The rings themselves were well
bracketed and bound together to ensure as much as
possible no danger from movement taking place. Not-
withstanding all these precautions, and despite the
fact that four rings of the rails had been properly
fitted in, collapse of the piling took place before the
bottom end of them had been reached. On this occa-
sion, however, no inrush took place, and even when
the displaced piles and rings had been withdrawn the
shaft did not fill up any further than the top of the
crib. Thus ended the seventh attempt to stop the
gap and reach the rock head, during which many
months of anxious labour had been spent.

The eighth experiment deserves particular atten-
tion, because not only was it crowned with success,
but it opens up new possibilities of great importance
in sinking and in other mining problems, such as
dams for holding back water, and stoppings for
isolating underground fires by hermetically sealing.

Compressed Air and Cementation.—This experiment
was nothing else than an adoption of the system now
known as the cementation process, and consisted of

forcing liquid cement into the sand behind the brick-
work. For this purpose two rows of 12 holes each
were drilled, one row at 3 ft. and the other at a
distance of 6 ft.' above the crib. The brickwork being
2 ft. in thickness, the holes were bored 21 in. long
by 2J in. in diameter. A piece of 1^ in. tubing with
a screw or flange on its outer end was then inserted
in each, and afterwards cemented or grouted in.
When the cement holding the tubes in position had
set, a in. cock was screwed on to the end of each,
and the holes then bored through the walling with
a smaller drill, which finished the hole at 1| in.
diameter. As soon as the drill pierced the wall the
sand blew out with great pressure, but when the drill
had been withdrawn and the cock shut, the flow of sand
was effectively stopped. After all the other holes had
been finished likewise, steps were then taken to fit
in the apparatus for forcing liquid cement in through
the tubes.

This apparatus consisted of two small egg-ended
steel boilers, 4 ft. long by 2 ft. diameter, fitted with
packing glands at each end, through which passed a
longitudinal spindle or shaft. On this shaft were fixed
several blades shaped like a propeller, which when
turned mixed the cement and water and kept it from
setting. (See fig. 5.) The boilers were fitted with a

Fig. 3.—Elevation of Rails Built in
Brickwork.



Fig. 4.—Plan and Sectional Eleva-
tion showing Inrush and Subsidence
from Surface.

i!'

1| in. tube for admitting compressed air- and a 2 in.
outlet, to which was attached a 2 in. metallic hose for
forcing the cement through the walling.

Before commencing cementation proper, it was con-
sidered advisable to apply the compressed air freely
to each of the holes, in order to make sure that each
was clear to take in the cement. In the course of this
a discovery was made, which is of great importance.
After the compressed air had been applied to about
eight or nine holes of the lower ring, an unusual
commotion occurred. It began by a heavy escape of
air from underneath the crib. The compressed air
had found an outlet down behind the brick lining,
and escaped out at the bottom edge of the crib in
the shaft. On looking down to see what was the
cause of the noise, the sand appeared to be creeping
up. It was thought that the compressed air had
either blown out fresh quantities of sand into the
shaft, or that it had got under the sand in the pit
bottom and was forcing it up. No time was lost then
in turning off the air pressure and preparing for a
hurried retreat, when the commotion ceased and all
was again still. An examination revealed the fact
that the sand was now nearer to the fixed scaffold
by 2 ft., but it was now stationary. Air was again
applied to the remaining holes of the lower row, all
the while watching closely its effect on the sand under-
neath, A similar but lesser commotion occurred,

which also ceased on the withdrawal of the air pres-
sure, and the sand was again noticed to be nearer to
the scaffold by another 6 in. Several other applica-
tions of air had similar but lesser results until the
supposed upward motion of the sand had ceased, and
it had now reached a point of about 4 ft. nearer the
scaffold than when the air was first applied.

A subsequent closer examination disclosed the fact
that the foregoing commotions were due not to the
sand coming up, but to the sinking of crib and brick
work, a most unexpected but none the less welcome
occurrence. The whole fabric had moved with the
application of the compressed air behind 'the brick-
work. It appeared that the air had been sufficient to
cause the sand and mud to loose their grip of the
brickwork and allow it to slide down as required. In
any case it did slide down more than enough to com-
pletely close the. hole from which the inrush of sand
and mud had so often taken place. It is obvious now
that an earlier application of compressed air to both
shafts would have expedited the sinking and reduced
the cost considerably.

Although the need for cementation was now much
less, it was decided to carry it out as originally
planned, as all the necessary apparatus for that
purpose were at hand.

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Fig. 5.—Process of Cementation.

Fig. 6.—Building of Brickwork in
Segments below Crib.

The first procedure was to take off the manhole door
of the boiler and half fill it with water, into which
afterwards was emptied cement enough to make the
required consistency. During the whole time the
handles attached to the shaft with the stirrers were
kept turning in order to thoroughly mix the cement
and water and' keep it from setting. The manhole
door was then replaced and screwed up tight, and
the compressed air at 80 lb. per sq. in. turned on.
The outlet cock was then opened and the handles kept
turning until the boiler was emptied and the air blew
freely through. This procedure was repeated as long
as the holes continued to take in cement. One of the
holes took in as many as 40 bags of cement, while
another took in only 8 bags. This was continued
until there was no longer any water in the pit bottom
to mix with the cement. The growth of water in the
pit bottom up to the start of the cementation process
was about 80 gals, per minute, but when cementa-
tion had finished the shaft was dry. the cement having
effectively dammed the water back and prevented it
flowing into the pit bottom.

The cementation therefore had not been in vain,
and while it was not required to close the hole from
which the inrush had taken place, it succeeded in
stopping the water, which is always a source of danger
when dealing with sand and soft mud. It had the
effect, however, of preventing the crib and brick lining