June 23, 1916.

THE COLLIERY GUARDIAN.

1187

the difference of the brine temperatures at the delivery
and return does not exceed 3 degs. Cent. (5-4 degs. Fahr.).
As a general rule, it is 2 degs. or 2’5 degs. Cent. (3*6 degs.
to 4* 5 degs. Fahr.). Thermometers are placed in the
ground between the freezing tubes and, if the circum-
stances allow, at the outside of the bore shaft or freezing
cellar, to indicate and control the progress of freezing. In
the case of very deep shafts it is possible to measure the
temperature at several different levels. "When a
maximum thermometer is inserted in the central hole it
must be placed in a shell, which will protect it from the
pressure of the water at various depths. From observa-
tions made at Winterslag Colliery, near Genck (Belgium),
it was clearly seen that the water remained warmer for
a long time in the centre of the borehole than at the
bottom (755 ft.) or at the top; this was probably due to
a small underground current. When the ice wall is com-
pleted, the water level inside the shaft will rise in conse-
quence of the formation of the ice. In order to ascertain’
whether the ice wall is completed, some of the water in
the central tube may be withdrawn, and if the water
does not assume its previous level it is proof that the ice
wall is complete. If its level cannot be reached because
of excessive depth, it will rise in the central tube; and if
this central tube be filled up, the water will not run away
into the ground when the ice wall is closed.

Sinking.

It is advisable to commence the sinking before the
centre of the shaft is completely frozen, as greater pro-
gress can be made in the soft ground. Only explosives
that are unaffected by a low temperature can be used.
Dynamite freezes at a temperature of -13 degs. Cent.
( + 8-6 degs. Fahr.), but it can be -employed, under cer-
tain conditions, when the holes are not placed in close
proximity to the shaft sides. At the Houssu Colliery,
in 1887, an attempt wras made to accelerate the speed in
sinking by thawing the pit bottom with steam, but this
process was soon abolished, as it obstructed the whole
of the shaft bottom, and the sinkers were obliged to
work in very cold mud up to their knees.

The question of temporary lining has been the sub-
ject of a great deal of controversy. In Germany it is
seldom used. Should a leakage of brine occur, it is
recognised by a black speck on the white rimmed side
of the shaft, but timber lining would prevent this being
seen. The writer believes that sinking without tem-
porary lining is simply adopted to reduce the co-st, but
is of opinion that lining is absolutely necessary in ground
which, previous to freezing, was loose, such as gravel
and sand. Ice formed by the freezing acts as cement,
but would thaw if exposed inside the shaft, and great
risk would be incurred from pebbles falling into, the pit
bottom. Lining is usually unnecessary in chalk or marl,
whilst clay strata require exceptional care, as will be
described later.

Tubbing.

Formerly, it was a question whether tubbing put
inside an ice wall was safe, owing to the fact that the
low temperature would prevent the cement mortar stick-
ing. It was also thought that timber would split, and
that cast iron would become brittle. Fortunately these
fears had no foundation, and the freezing process allows
any of these tubbing methods to be employed. Brick-
work has, for example, been used in both shafts of the
Emilie Mine, the mortar being mixed with salt water,
and tar, and the shafts separated from the ice wall by
planking.

In Russia, small concrete plates have been fitted in
shafts of 16 to 20 ft. diameter, and 490 ft. in depth. If
timber be used, it must be absolutely dry, or it would
eventually freeze. The rectangular shafts in the
German lignite mines sometimes have wooden linings.
In France both shafts at Flines-lez-Raches (depth 246 ft.
and 297 ft., diameter about 14ft.), and shaft No. 3 at
Dourges Colliery (depth 187 ft., diameter about 15 ft.)
are lined with timber. Iron tubbing is principally used
in Great Britain, and preference is generally given to the
English system of tubbing built up from the bottom,
the jointing being made with wooden wedges and
wooden sheeting. At the Beeringen Colliery, corru-
gated tubbing was used for shafts about 1,600 ft. in
depth. Behind the tubbing, concrete is rammed in,
being mixed with chemicals to prevent it from freezing
before binding takes place. In many cases calcium
chloride is used for the purpose. Other chemicals have
been used, for instance, sodium sulphate (Na2S04) at
Bernissart Colliery, in Belgium; sodium carbonate
(Na2Co3) at Petite Rosselle, Lorraine; salt (NaCl) at
Llay Main Collieries; and a mixture of lime, calcined
soda, and magnesium chloride at the Carl Alexander
Colliery, Germany. No general rule, however, exists
as the composition of cement varies from place to place.
Salt (NaCl) has given excellent results in several Belgian
mines, but bad results in Holland. Sodium carbonate
(Na2 Co3) was good in many places, but at Petite Rosselle
it was a failure. CaCl2 increases the binding of cement
in some cases, and retards it in others. Therefore, it
is advisable that, in each case, tests should be made
with the cement to be adopted, to prove which is most
suitable for the circumstances. In shafts, where under-
hung tubbing is used, from the top to the bottom, it is
impossible to ram concrete in behind it, but liquid
cement is introduced through holes in the segments
after they have been assembled. This method has an
advantage in that time is gained, and temporary lining
is unnecessary, but, on the other hand, this type of
tubbing is not always absolutely watertight, and for this
reason the writer thinks it is better not to adopt it,
except in cases where a large bed of clay has to be
passed through. As already pointed out, clay will not
become so hard as other frozen ground. At the time
of sinking, it is liable to swrell very rapidly, and
frequently the pegs of the iron rings have been sheared
and the rings themselves crushed, thus constituting
a great danger, which before now has led to fatal
results.

Crib beds at different levels will alleviate the whole
column, besides having the advantage of saving the
finished portion of the shaft should an accident occur.
After thawing they do not, however, prove watertight;
on the ground side the resistance will become less and the
wedges will loosen, and for that reason the last crib beds
must always be inserted in good, solid rock below the
frozen area, and securely wedged. The plant must not be
stopped before the tubbing is complete throughout its
entire length. After thawing, the tubbing must always
be re-wedged. If there are extensive feeders these may
be stopped by injections of cement through holes bored
in the segments. It has been proposed to follow sinking
by a descending brick or cast iron cylinder, as was tried
at the Jessenitz mine, but, at a shallow depth, the
tubbing cylinder deviated to one side and stuck to the ice
wall.

Thawing.

When a shaft is complete, the ground is thawed natu-
rally by leaving it to the heat of the ground or artificially
by a circulation of hot brine through the freezing tubes.
In Germany, the tubes generally remain in the ground,
but in France and in Belgium they are frequently with-
drawn, each tube being warmed to soften the ground.
The withdrawal is by no means easy, the columns fre-
quently breaking in pieces and portions being lost. In
shafts with wooden tubbings it is necessary to fill the
shaft up with water when withdrawing the tubes. This
has also been done in the case of cast iron tubbing, at
Bernissart, but this proceeding tends to hide the water
feeders which may appear, and should be immediately
stopped.

At Jessenitz the shaft was filled with water at
+ 60 degs. Cent. ( + 140 degs. Fahr.) and maintained at
that temperature for two weeks. This arrangement
requires a considerable amount of steam for shafts
which are of any depth.

Occasionally the tubbing requires cement injections to
make it watertight. In such cases the bottoms of the
freezing tubes are pierced, and the tubes are withdrawn
in lengths of about 10 m. (33 ft.), cement being injected
after each withdrawal. This process was used for the
first time at the Simon shaft, No. 1, at Petite Rosselle,
and was attended with very good results.

Special Problems : Breaking of Tubes.

. It sometimes occurs that freezing tubes leak, and, in
consequence, brine flows into the shaft. This may be
due to various causes, such as badly-made joints, a defec-
tive system of joints or the bursting of a tube. In many
cases it is the result of carelessness on the part of the
sinkers in putting shot holes too close to the sides of the
shaft or charging too much explosive in the shot holes.
As soon as the leakage of brine is discerned it is necessary
to stop the circulation pump, and the tubes in the vicinity
of the leakage must be isolated by closing down their
circulation valves. It is then necessary to find the
defective tube, and when this is located, the inner tube
is withdrawn and a smaller tube inserted in place of the
old outer freezing tube. Inside the new tube a smaller
inner tube is fixed (two complete tubes being inserted
inside the original leaking tube), whereupon the new
column is connected to the freezing plant. The brine
which flows into the shaft can be collected in hoppits and
used over again. When a tube slants towards the shaft
and the neighbouring freezing tube comes just behind it,
the ice round this latter tube will exercise great pressure
on the first tube, and eventually cause it to break, espe-
cially after the sinking has relieved the counter pressure
from the middle of the shaft itself. In such case the
deviated tube will be discovered and the defective part
should be removed and replaced by a special tube bottom,
and re-connected again with the freezing plant, or a
smaller tube, as previously described, is inserted and the
freezing in that tube resumed.

Underground Current : Bursting of the Ice Wall.

Such an accident is at all times dangerous, and the
shaft must immediately be .filled up with soft water,
and no displacement must be made, as it would create
an artificial current of relatively warm w’ater through
the opening, which would quickly increase. The water
introduced into the shaft exercises a counter pressure,
which diminishes the feeder, and even stops it by trans-
forming it into ice. The causes of rupture of the ice
wall are many. At the Friedrich Heinrich Collieries,
the ice wall was probably weakened by the fact that
three freezing tubes deviated towards the shaft, so that
several of the other freezing tubes had a very large space
between them. The frozen clay did not offer sufficient
resistance to withstand the pressure, and thus contri-
buted to the cause of the breakage. From the same
cause, an accident occurred at No. 2 shaft, Winter slag
Colliery, where a portion of the shaft was only tem-
porarily lined. In cases of this description, it is neces-
sary to make supplementary boreholes in the frozen
ground, but it is essential that brine solution or hot
water should be used in place of cold water during the
borings.

At Auboue, the ice wall was strengthened by the aid
of cement in the neighbourhood of semi-frozen tubes.
The cement was put in behind the tubbing, the shaft
was filled with water, and in three weeks’ time the
damage .had been repaired. At No. 2 shaft of the
Ligny-lez-Aire Collieries, the water level was at about
40 yds. depth, when water came in through large fissures
from a hill in the vicinity. To stop this current it was
found necessary to insert six small freezing tubes in
the shaft just in front of the fissures inside. A similar
difficulty was encountered at No. 2 shaft of the same
colliery. Large cavities and underground ‘currents of
water gave great trouble to the freezing at Bullcroft
Colliery, but this shaft was completed by partly filling
the cavities with cement, and adding a second com-
pressor to the existing freezing plant. A similar thing
occurred at the Prince Adalbert shaft, near Oldau, Ger-
many. Large excavations had been made in the sand
during the course of the boring, and so caused a great

shrinkage, with the result that the buildings containing
the winding engine and the freezing plant were greatly
damaged.

Hot Water : Salt.

If, at a certain depth, hot springs are encountered,
freezing is almost impossible, especially if the water
contains salt. Strata of this description exist in parts
of the recently discovered coal field near Nancy,
France. With the presence of saturated salt water, the
ice wall is liable to be broken, as occurred at the
Ronnenberg Mine a few inches above a supposed
gypsum bed, which was to carry the last crib bed, but
proved to be only a large block overlying the rock salt.
Formerly, such shafts could only be completed by the
Kind-Chaudron method, by reducing their diameter, but
it is now possible to completely freeze saliferous strata
which are at the ordinary geothermic temperature, as
is the case in the potash mines of Central Germany and
Alsace. To produce the very low temperature neces-
sary, for example, — 40 to — 70 degs. Cent. (— 40 to
— 94degs. Fahr.), carbonic acid compressors must be
used with denatured alcohol as circulating medium.
Sinking in such shafts is a difficult proposition, as fur
clothes and hot drinks are necessary. The first trial,
which was a failure, was made at the Nieder-Sachsen
mine, but improvements took place at Prince Adalbert
mine in 1910, where the first portion of the shaft had
already been sunk by the ordinary freezing method, and
the plant produced the low temperature of —40 degs.
Cent. ( — 40 degs. Fahr.) necessary for the solidification
of concentrated brine. Since then, several other shafts
have been sunk on these lines.

Intermittent Freezing.

After the great success which attended the freezing of
shafts of medium depths- it was natural to adopt it for
greater depths, but the trouble of deviations was greatly
feared. To overcome this it was proposed to freeze only
short lengths at one time, and gradually decrease the
diameter of the shafts as in the case of piling. When a
certain depth had been sunk a concrete plug was placed
in the bottom of the shaft. Guide tubes leading to the
surface were inserted. This was to establish the
equilibrium of the water level when boring was com-
menced from the plug. Several patents have been taken
out for this process, and the descriptions of two of them,
namely, Unger and Grotevrath and Hillenblink, have been
published, but the writer is not aware that they have
found any practical application. The great drawback
would be that the shafts would have an enormous starting
diameter, each section reducing the diameter to allow a
shaft of normal size at completion.

Often in shafts which have been sunk to a . certain
depth, waterbearing strata are encountered, and this
necessitates freezing. To accomplish this, vertical tubes
are inserted inside the shaft, and after the ice .wall is
closed a small shaft is sunk, and finally the shaft is
enlarged from the bottom to the original shaft crib by
excavating the ground behind the tubes. It has been
assumed that the cold produced by the freezing tubes
would keep up’the ice wall while the tubbing is being
created, but the tubes become quickly covered with rime
and lose a great deal of their conductivity, with the result
that the ice wall breaks. Accidents of this description
occurred at the Centrum mine at about 110 ft., at
Jessenitz, at 490 ft., and at Hansa Silberberg at 260 ft.
Better success has been attained by inside freezing, with
oblique boreholes, and several shafts have been sunk by
this method.

The work proceeds as follows :—The pit is gradually
enlarged in order to obtain a diameter about 5 ft. larger
than the inside diameter of the tubbing, then a cast iron
curb, having the same diameter as the unlined shaft, is
cemented on to the bottom of the enlarged shaft. It
has slightly oblique flanges, into which inclined pipes
several yards in length are screwed. These pipes are
embedded in concrete, and are connected near the place
where the enlargement of the shaft commences. The
boring bit and rods are introduced into these tubes. The
boring, which is commenced from the bottom of the
inclined guide tube, is oblique for a short distance, but
eventually becomes vertical. Any water which rises
during boring is prevented from flowing into the shaft,
as it is carried to the surface by the tubes. These tubes
are supported by collars, which are fixed at depths of
about 33 ft., 330 ft., and 740 ft. If, during the boring,
some of the lining, tubes in the ground break, other
tubes of smaller diameter are inserted. The boring
must be carried on with muddy water to prevent the
sand rising in the tubes. In each borehole a freezing
tube is inserted, and a watertight joint is made between,
the freezing tube and the guide tube near the point
where it goes through the curb. Cement is then
injected to completely insulate the water-bearing strata
below from the upper portion of the guide tubes. When
this is done the guide tubes can be emptied of water.
The brine mains are placed close to the surface. During
the freezing it is necessary to have a tube which pro-
vides an escape for the water confined in the cylinder
formed by the ice wall, and terminated at each end by
the concrete plug and the watertight ground. This
method has given excellent results, but the work to be
done takes a long time, and requires great care. The
deepening of the Houssu shaft required 2| years, but
in this case the freezing plant was too small. At Borth
the following system was adopted :—The bottoms of the
guide tubes were embedded in a block consisting of
three parts—first, the concrete bed; second, a grave]
bed; and third, a concrete bed. After completing the
boreholes inside the guide tubes in the usual way,
cement was injected in the gravel bed to ensure an abso-
lutely watertight plug. Then this had to be increased
by coils embedded in the upper concrete. These coils
surrounded the freezing tubes, and were attached, to- the
circulation-of cold brine, which was expected to make
an ice joint quickly. After inserting the freezing tubes
and withdrawing the guide tubes, the brine mains were