Ice crib

An ice crib for use in retreat mining to support the overburden is formed of fresh water ice, the freezing and melting of which is controlled in situ by flow therethrough of temperature regulated brine.

The present invention relates to mining equipment and, more particularly, 
to ground support equipment for use in underground openings. 
In underground mining, pillars are left within any mined cavity or room in 
order to provide support for the overburden. Usually, attempts are made at 
recovering the material of value represented by the pillars before 
abandonment of the mined area or termination of the mining operation. 
Particularly, in coal and other mining operations, mechanical means are 
usually employed to serve the function of pillars. 
During recovery of the pillars or mechanical substitutes therefor, a 
continuing danger of injury, loss of life, damage or burial of equipment 
continually exists. 
In U.S. Pat. No. 1,207,569 there is described a method for supporting the 
roof of mine tunnels or other underground cavities during second mining 
operations and to provide a substitute for the pillars to be mined, props, 
cogs or pillars that have become weakened. It is suggested that the mine 
cavities be filled with blocks of ice, which ice is caused to flow to fill 
all of the cavities by placing the ice under very substantial pressure. A 
similar system of employing ice flow is described in U.S. Pat. No. 
3,790,215. Herein, the mine is filled with ice which ice progressively and 
continuously flows during the primary mining operation to provide 
requisite support for lateral and hanging rock walls. Necessarily, a very 
substantial pressure equivalent to a vertical height of twenty-two or more 
meters of ice is necessary. 
Roof supports in the configuration of air inflatable tires are described in 
U.S. Pat. No. 2,861,429. Structure is also described therein for 
accommodating transport of such supports from one location to another 
within the mine. U.S. Pat. No. 2,990,166 is directed to air inflatable 
cushions cylindrical in configuration. U.S. Pat. No. 3,508,408 is directed 
to a pneumatic cushion particularly adapted for coal mines and having 
particularly oriented multiple plies of textile cords extending helically 
thereabout. U.S. Pat. No. 4,072,015 is directed to air inflatable bladders 
for plugging bore holes to permit injection and containment of a fluid 
within the bore hole to provide ground support for the bore hole. 
The present invention is directed to a crib formed of ice to serve as a 
pillar for support of the overburden. The apparatus employed includes a 
length of two concentric tubings rolled or folded upon itself to provide a 
cross-section, when inflated, equivalent to that of the space to be 
occupied. Fresh water is injected into the outer tubing and brine, chilled 
to a temperature below zero degrees centigrade, flows continuously through 
the inner tubing. The brine will draw off heat from the surrounding fresh 
water and in due course the fresh water will freeze. The resulting block 
of ice will provide structural support in the manner of a pillar or other 
support whether a jack, a concrete column or a timber crib. On completion 
of the mining operation and to bring about cave-in, the flow of chilled 
brine may be stopped to permit gradual melting of the ice; alternatively, 
non-chilled brine may be passed through the block of ice to draw off heat, 
promote more rapid melting and partially chill the outflowing brine for 
use in constructing other ice cribs. The melting of the crib is relatively 
slow which provides adequate time for evacuation of all equipment and 
personnel prior to cave-in. It may also be noted that water expands when 
it freezes, which expansion serves in the manner of providing a 
pre-stressed pillar for the roof, drive or drift within which the ice crib 
is to be formed. This capability exists only with very expensive 
mechanical jacks. 
It is therefore a primary object of the present invention to provide an 
inexpensive readily erectable ice crib. 
Another object of the present invention is to provide a pre-stressed ice 
crib. 
Yet another object of the present invention is to provide an expendable ice 
crib. 
Still another object of the present invention is to provide structure for 
forming an ice crib of unlimited size and configuration. 
A further object of the present invention is to provide an ice crib 
automatically conformable to the space within which it is to be used. 
A yet further object of the present invention is to provide an ice crib for 
underground openings which will permit on command the ground to subside 
and close the underground openings. 
A still further object of the present invention is to provide an ice crib 
compactible for storage and transportation. 
These and other objects of the present invention will become apparent to 
those skilled in the art as the description thereof proceeds.

Referring to FIG. 1, there is shown a mine having an underground room in 
which retreat mining is in progress and prior to robbing the pillars. A 
plurality of drives (drifts) 10, 12, 14, 16 and 18 intersect one or more 
of panels (cross cuts) 20, 22, 24 and 26. A plurality of pillars are 
defined by the respective circumscribing drives and drifts, which pillars 
provide support for the overlying ground or overburden. 
The pillars represent material of value to be mined but mining of the 
pillars by retreat mining would cause subsidence and cave in of the 
overburden unless support therefor were maintained. These pillars are 
identified by reference numerals 28 through 39. The mining limit of the 
mine is identified by reference numeral 40, which limit represents the 
extent to which mining may be conducted as a result of limitations in the 
lease or ownership of the ground. Similarly, drives 10 and 18 represent 
the lateral extent to which the mine may be mined. 
Prior to mining of any of the pillars, the present invention is employed to 
develop a block of ice located within one or more of the drives and drifts 
to provide support for the overburden during mining of the pillars. These 
blocks of ice produced by the present invention and referred to as ice 
cribs are identified by numerals 42 to 46. It may be noted that the ice 
cribs formed vary in length to meet the requirements of each particular 
location and which variability is a feature of the present invention. 
Moreover, ice cribs 42, 43 and 44 provide vertical support for the 
overburden and extend between the left and right sides of the respective 
drives and panels and to mining limit 40. Ice cribs 45 and 46 provide 
support for the overburden and extend between the left and right ribs 
within drive 12. 
After erection of ice cribs 42 to 46, the first cut made in each pillar is 
adjacent the respective ice crib and identified by the letter A. On 
completion of each cut A, an ice crib is formed in the space vacated to 
provide a temporary substitute support for the overburden. Further cuts B 
and C are made successively in each pillar. After each such further cut, 
if needed, a further ice crib is substituted in place of the cut to 
provide support for the overburden when required and dependent upon the 
structure and composition of the overburden. After each pillar has been 
removed, the support previously provided thereby is now obtained from the 
respective ice crib(s). Such support will continue until the ice crib(s) 
melts. 
By controlling the rate of ice melt of each ice crib, the rapidity of 
subsidence of the overburden can be controlled. Such control affords total 
and complete removal of all mining equipment, materials and personnel from 
each given area to eliminate injury or loss due to rock burst or 
subsidence. It may also be pointed out that as no timber cribs, metal 
jacks, chocks or other equipment need be recovered by personnel, the 
safety hazards attendant such recovery are totally eliminated. 
Because of the relatively low cost of the structure of which each ice crib 
is formed, nonrecovery thereof is generally affordable; the loss of the 
ice crib structure may be somewhat ameliorated by using the melting ice 
crib as a heat sink to chill the fluid to be used in forming other ice 
cribs. An ice crib used as a heat sink will acquire heat more rapidly than 
otherwise. The heat acquisition can be regulated to some extent and 
thereby be used to melt the ice crib at a relatively controllable rate. 
Referring to FIG. 2, there is shown a room containing material of value to 
be mined by the pocket and wing method. The room is bounded by drive 48, 
drift 50, limit 52 defining an edge of gob and limit 54 defining a further 
edge of the gob. First, a pocket 56 is mined from drift 50 to limit 54. 
Secondly, a further pocket 58 is mined from pocket 56 to limit 52. Prior 
to the mining of these pockets and to provide support for the overburden 
which may be needed as a result of the unsupported area defined at or 
about the intersection of pockets 56, 58 and drift 50, ice crib 60 is 
developed at the end of drift 56 adjacent limit 52. 
The mining of pillar 62 of material of value bounded by pockets 56, 58 and 
limits 52, 54 is made by taking successively a plurality of angled cuts 
64, 65, 66, 67, 68, 69 and 70. On completion of one or more of the cuts, 
ice cribs 72, circular in plan form as illustrated, may be erected within 
the areas defined in FIG. 2 as pockets, 56, 58 and cuts 64 through 70. Ice 
cribs 72 may be of different size (diameter), depending upon the 
composition of the overburden and the resultant loads to be supported. The 
placement of ice cribs 72 is similarly to be determined by the structural 
integrity of the overburden and will vary from location to location. 
Accordingly, the placement thereof depicted in FIG. 2 is to be construed 
only as representative of the ice crib size and location of placement. 
The material of value to be mined between pocket 56 and drive 48 is divided 
into two areas by mining a further pocket 74 extending from drive 48 to 
pocket 56. Prior or subsequent thereto, ice crib 76 may be erected within 
drive 48 adjacent limit 54 as a substitute for the support withdrawn by 
mining of the material of value. 
Pillar 78 is mined by a series of angled cuts 80, 81, 82, 83 and 85. 
Subsequent to one or more of these cuts, further ice cribs 88 may be 
located within pocket 74 and in the areas represented by one or more of 
the cuts made into pillar 78. Again, the number and size of ice cribs 88 
is primarily dependent upon the composition and structural integrity of 
the overburden. 
Pillar 90 is mined by taking a plurality of cuts 92, 93, 94, 95, 96 and 97. 
Subsequent to taking one or more of these cuts in pillar 90, further ice 
cribs 100 may be located within drive 48, drift 50 and one or more of the 
areas represented by cuts 92 to 97. Again, the selection of size and 
number of such ice cribs is dependent upon the composition and structural 
integrity of the overburden. 
After all of the material of value has been removed from the room bounded 
by drive 48, drift 50 and limits 52, 54, subsidence or cavein of the 
overburden may be undertaken. By selective melting of ice cribs 60, 72, 
76, 88 and 100, controlled and regulated subsidence may be accomplished. 
Preferably, the melting of the ice cribs is regulated to extend uniformly 
from limits 52, 54 to drive 48 and drift 50. 
It may be appreciated that all mining equipment and materials to be removed 
from the room can be so removed substantially in advance of any 
subsidence. Furthermore, all personnel can and will be evacuated long 
before any subsidence occurs. Therefore, loss of equipment and material is 
avoided and hazards to personnel as a result of the subsidence are totally 
eliminated. 
Referring to FIG. 3, there is illustrated an elevational view of a 
conventional drive or drift, such as illustrated in plan view in FIGS. 1 
and 2. As soon as the material of value has been removed to form the drive 
or drift, floor 102 begins to heave and roof 104 begins to sag. This 
usually results in separation 109 between beds 106, 108 and beds 110, 112 
and 114. The separation further weakens the structural integrity of the 
roof and at some point failure will occur resulting in partial or complete 
closure of the drive or drift. 
A conventional timber crib 116 is illustrated in FIG. 4. Such a timber crib 
is placed within an opening or drive or drift to provide physical support 
between floor 118 and roof 120. The timber crib will generally halt 
further bed separation for a period of time. However, the continuing 
pressure placed upon the timber crib coupled with the fact that a timber 
crib is compressible will still result in continuing but decelerated sag 
of roof 120. At some point in time, and it is only a matter of time, 
subsidence or cavein will occur. It may also be noted that the timber crib 
is generally not recoverable without substantial hazard to both equipment 
and personnel. Alternatives to the traditional timber crib are hydraulic 
jacks which can be expanded in a manner a wooden crib cannot be and any 
separation between the layers in a roof or floor can be closed; but, such 
hydraulic jacks are too expensive to be used as disposable items. On 
removal thereof, hazards to both equipment and personnel will and do 
exist. Other means such as chocks of various types have been used but the 
underlying problems continue to remain with a change being only one degree 
of severity. 
Referring to FIG. 5, there is shown an opening 122 of a drive or drift, of 
the type shown in FIG. 3. To support roof 124 and prevent separation of 
beds 126, 128 in floor 130 and between beds 132, 134 and 136 in the roof, 
an ice crib 138 is placed therein. The ice crib includes an envelope 140 
generally defining the height, width and length of the ice crib and which 
envelope is generally commensurate with the cross-section of opening 122 
and the length along which the ice crib is to provide support. On freezing 
of the water to form the ice crib volumetric expansion occurs. Such 
expansion results in preloading or prestressing the beds of floor 130 and 
roof 124 to preclude any separation from beginning, or, if it has begun, 
to close any separation between the beds in the floor and/or the roof. 
Thus, the benefits of a hydraulic jack are achieved by the ice crib and 
yet the expenses attendant a hydraulic jack, both in terms of capital 
costs, maintenance and labor are obviated. 
To reduce the rate of heat flow to ice crib 138 from floor 130 or roof 124, 
pads of insulation 142, 144 may be employed. Such pads of insulation also 
have a secondary benefit in that uneveness of both the floor and the roof 
are somewhat accommodated by penetration into the pads and thereby reduce 
the degree and extent of any stress concentrations that would otherwise be 
produced in envelope 140 of the ice crib. 
Referring jointly to FIGS. 5, 6 and 7, there is shown a method for punch 
mining and with which method the ice cribs are particularly useful. The 
process of punch mining is generally employed where the structural 
integrity of the layers in the overburden is low or otherwise requires 
closely spaced pillars or supports to prevent subsidence or rock burst. As 
will be described hereinafter, no pillars of material of value need be 
left in the punch mine process to be described and illustrated in FIGS. 6, 
7 and 8. An initial punch mine opening 150 is shown in FIG. 6. This 
usually results in some separation between beds 152, 154 in floor 156 and 
between beds 158, 160 and 162 in roof 164. 
On placement of an ice crib 166 within opening 150, as shown in FIG. 7, the 
separation between beds 152 and 154 and beds 158, 160 and 162 are closed 
or at least further separation is precluded because of the pressure and 
support provided by the mass of ice crib 166. Thereafter or commensurate 
with mining of opening 150, a second opening 168 can be mined. The 
separation in the beds of the floor and roof attendant opening 160, as 
described with respect to FIG. 6, will again exist. Such separation and 
the resulting voids can be closed by erecting in the opening a further ice 
crib 170 as shown in FIG. 8. 
Pillar 172 of material of value intermediate ice cribs 166 and 170 may now 
be mined as the floor and roof adjacent thereto have been stabilized by 
these ice cribs. After an opening 174 is formed, further separation of the 
attendant floor and roof may occur. Such separation, assuming that 
subsidence of the overburden is not yet desired, can be halted or 
corrected by erecting a further ice crib within opening 174. After all 
material of value has been removed by mining a plurality of openings in 
the same or similar manner described above, subsidence of the overburden 
may be achieved in regulated and controlled manner by selective melting of 
the various ice cribs. The requirements attendant present mining 
techniques of having to leave pillars of material of value intermediate 
openings are obviated by the ice cribs. Again, it may be noted that all 
hazards and potential losses attendant equipment, materials and personnel 
as a result of the dangers attendant prior art planned subsidence or 
accidental subsidence have been obviated. 
Referring to FIG. 9, there is illustrated an apparatus 176 formed by a 
double walled tubing 178 having an inner tube 180 and an outer tube 182. 
Closure means, such as end cap 184 extends across the mouth at each end of 
outer tube 182. An aperture 186 is provided in the end cap to accommodate 
passage of inner tube 180 or an extension 188 thereof therethrough. A pipe 
190 or like passageway extends through aperture 192 in the end cap. The 
pipe provides a means for fluid communication with the interior of outer 
tube 182; that is, the annular space between the inner and outer tube. One 
or both ends of pipe 190 may include a coupling 194 for interconnecting 
the pipe with another segment of double wall tubing 178 to provide fluid 
communication therebetween; alternatively, the coupling may be replaced by 
a plug or other closure means to prevent flow through pipe 190. 
Outer tube 182 serves as an envelope for containing a first fluid, such as 
fresh water, which is to be frozen to form the ice crib. Inner tube 180 
serves as a conveying means for conveying a second fluid chilled below the 
temperature of the first fluid to draw heat from the first fluid and 
reduce its temperature. 
Still referring to FIG. 9, a support system for operating the double wall 
tubing to convert it to an ice crib will be described. A water source 196 
is interconnected with pipe 190 through conduit 198 to provide a flow of 
water into outer tube 182. An air source 200 may be selectively 
connectible to conduit 198 to provide an initial inflation of the outer 
tube to position the double wall tubing within the space the ice crib is 
to be formed. Closure means 194 may include means for expelling the air 
initially injected within outer tube 182 upon inflow of water from water 
source 196. After outer tube 182 has been filled with water, a cooling 
medium, such as brine, is pumped by pump 206 from a brine source 202 
through a refrigeration system 204 to chill the brine to a temperature 
below the freezing temperature of the first fluid, or fresh water, through 
conduit 208. The out flow of brine through extension 188 is conveyed 
through conduit 210 back to the brine source. 
As alluded to above, during deliberate melting of any ice crib, inner tube 
180 thereof may be connected to the inner tube of another ice crib to be 
formed to precool or prechill the fresh water within the ice crib to be 
formed. This procedure serves two purposes. First, it can be used to 
accelerate melting of an existing ice crib; and, secondly, the resulting 
lowered temperature of the brine flowing into the ice crib to be formed 
will draw heat from the fresh water attendant the ice crib to be formed 
and thereby certain savings in refrigeration costs may be effected. 
The apparatus illustrated in FIG. 9 from which an ice crib is to be formed, 
is, preferably, in the configuration of an elongated tube. Such a 
configuration permits folding or coiling of the tube to form almost any 
configuration necessary to fill the space within which an ice crib is to 
be formed. 
Referring to FIG. 10, there is shown an ice crib 212 having an envelope 214 
of a configuration commensurate with that of the ice crib to be formed. 
Within the envelope, the apparatus for containing and freezing the water 
is coiled, folded or otherwise positioned to occupy the requisite volume. 
It may be noted that a sheet of insulation 216 and 218 is located 
intermediate the overburden and the top of the envelope and the floor and 
bottom of the envelope, respectively. The use of such insulation serves 
two functions: First, it reduces heat transfer into the ice crib and 
thereby aids in prolonging melting of the ice crib; Secondly, it provides 
a means whereby the amount of pressure to be exerted by the ice crib upon 
freezing can be regulated through the known force necessary to partially 
or completely compress the sheets of insulation. As mentioned above, a 
third benefit available is that of shielding optional envelope 214 or the 
apparatus therein against puncture by pointed or sharp objects extending 
upwardly from the floor or depending from the overburden. 
FIG. 10 also illustrates in partial cutaway view a cross-section of the 
apparatus shown in FIG. 9 folded upon itself in serpentine manner to 
occupy the space defined by envelope 212. For ease of installation and to 
insure that all of the space within the envelope will in fact be filled 
with fresh water and brine in their respective tubes, the double wall 
tubing may be first inflated to the size it would be were water and brine 
disposed therein. Evacuation of the air within the apparatus could be 
accomplished by a vacuum pump or simply by filling the outer tubing with 
water, as described in reference to FIG. 9. It may be noted that inner 
tube 180 is lodged naturally at the bottom of outer tubing 182. Such 
positioning assumes that the inner tube is free to float or sink within 
the outer tube. The inner tube is assumed to conduct a salt brine rather 
than less dense but more expensive glycol brine, and thus sinks in the 
fresh water in the annular space. The use of the concentric tubes 
positions and distributes the inner tubes evenly throughout the space to 
be filled with ice. The added expense of employing supports on positioning 
members to carefully position the inner tube with respect to the outer 
tube presently appears unjustified. As illustrated, a valve 220 may be 
interconnected with inner tube 180 or an extension thereof to regulate the 
flow rate of brine through the inner tube. 
After each ice crib has been erected, the fresh water and brine 
interconnections therewith may be severed in the event continuing flow of 
chilled brine is unnecessary to maintain the ice crib frozen for the 
period of time during which it must provide the requisite support for the 
overburden. Alternatively, the connections may be retained intact to 
provide a means for continuous flow of chilled brine to insure non-melting 
of the ice crib during the period of time within which it must provide the 
requisite support of the overburden to remove the hazard and danger to 
equipment and personnel performing a mining function. Where the economies 
so justify, an existing ice crib which is to be melted, can be employed to 
precool the brine flowing into the refrigeration system and from which it 
flows into an ice crib to be formed. The resulting savings in 
refrigeration costs override the costs attendant the necessary conduit and 
fittings. Furthermore, by transmitting non-chilled brine through an 
existing ice crib, the melt rate thereof may be reasonably accurately 
controlled by regulating both the flow rate and temperature of the brine 
flowing into the ice crib. The chilled fresh water from a melted ice crib 
can also be pumped into an ice crib to be formed; or, it can be simply 
pumped out to collapse the ice crib. 
The apparatus illustrated in FIG. 9 may be formed of relatively inexpensive 
tubing of man-made plastic materials and inexpensive plastic fittings as 
the pressures attendant operation of the apparatus are well within the 
limits of such materials. Thereby, the apparatus may be considered to be 
disposable and in fact it is probably less expensive to permit it to 
become buried in a cavein than to expend the funds necessary to retrieve 
it, handle it, transport it and store it. It may be noted that the 
pressures resulting from the support provided by an ice crib are borne by 
the ice and not the envelopes or tubing therefor. 
Since apparatus 176 is collapsible, it is readily and economically storable 
and transportable. Moreover, it is simple to set up and operate which 
reduces the level of skilled manpower necessary for such purposes. 
While the principles of the invention have now been made clear in an 
illustrative embodiment, there will be immediately obvious to those 
skilled in the art many modifications of structure, arrangement, 
proportions, elements, materials, and components, used in the practice of 
the invention which are particularly adapted for specific environments and 
operating requirements without departing from those principles.