US3525551A

US3525551A - Method of mining thick coal seams

Info

Publication number: US3525551A
Application number: US798652A
Authority: US
Inventors: Richard G Mallander
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1969-02-12
Filing date: 1969-02-12
Publication date: 1970-08-25
Anticipated expiration: 1987-08-25

Description

Aug. 5, 1970 R. G. MALLANDER METHOD OF MINING THICK COAL SEAMS Filed Feb. 12, 1969 INVENTOR. RICHARD G. MALLANDER ATTOR NEYS United States Patent O 3,525,551 METHOD OF MINING THICK COAL SEAMS Richard G. Mallander, Wheatridge, Cl0., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Feb. 12, 1969, Ser. No. 798,652 Int. Cl. E21c 41/00 US. Cl. 299-11 5 Claims ABSTRACT OF THE DISCLOSURE The top layer of an underground thick coal steam is mined, leaving coal pillars running from the top surface of the remaining coal seam to the roof to support the roof. These coal pillars are reinforced with wrapping and coating, and a next layer of the coal seam is mined, leaving the reinforced coal pillars and coal pillar extensions thereof, these resulting pillars extending from the upper surface of the remaining coal seam to the roof to support the roof. Such procedure is repeated until the full depth of the coal seam is mined.

BACKGROUND OF THE INVENTION This invention relates to mining, and, more particularly, to a method of mining thick underground seams of coal.

Using known procedures, the mining of underground coal seams thicker than -15 feet has created serious problems. If the seam is near the surface of the earth, it is of course possible to remove the roof or overburden from the coal and expose the coal for conventional surface mining However, when the overburden itself is quite thick, the cost of removing it becomes too great to make the mining operation economically feasible, and underground mining methods must be followed.

One of the chief problems existing in underground mining is the necessity of supporting the overburden or roof so that danger to men and equipment is kept to a minimum, meanwhile mining as much coal as possible from the seam so as not to waste this natural resource.

In mining a layer of coal 10-15 feet thick from an underground coal seam, one of the conventional methods is to remove as much coal as possible, while leaving a plurality of coal pillars to support the roof. In such an application, the problem of pillar strength is not considered too severe. However, in thick seams (perhaps 30-90 feet thick), if this same method was applied, 50% or greater of the coal would be needed as pillars to ensure that the roof is properly supported.

It is an object of this invention to provide a method of mining underground thick coal seams, utilizing pillars of coal to support the roof in a proper manner.

It is a further object of this invention to provide a method of mining underground thick coal seams which, while fulfilling the above object, provides as much yield of coal as possible from the thick seam.

SUMMARY OF THE INVENTION Broadly stated, the inventive method of mining coal from a seam beneath a roof comprises removing a top layer of coal while leaving coal pillars which extend from the upper surface of the remaining coal seam to the roof to support the roof. At least a portion of each coal pillar is wrapped with a wrapping member, and at least a portion of each coal pillar is coated with a seal coat, the wrapping and coating serving to reinforce the coal pillars. A next layer of coal is removed immediately below the removed layer while leaving the reinforced coal pillars and downward coal pillar extensions thereof, the resulting pillars extending from the upper surface of the remaining coal seam to the roof to support the roof.

3,525,551 Patented Aug. 25, 1970 BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the invention will become apparent from a study of the following specification and drawings, in which:

FIGS la-ld show the sequence of the breakdown of a conventional coal pillar when used in the mining of an underground thick coal seam;

FIGS. 2a -2g show the sequential steps of the inventive method disclosed herein.

DESCRIPTION OF THE PREFERRED EMBODIMENT Shown in FIG. 1a is a conventional coal pillar 10 used in the mining of a thick coal seam 12. Such coal pillar 10, which is of course one of a plurality of coal pillars, runs from the top surface 14 of the remaniing coal seam 12, after a thick layer of coal 16 has been mined, to the roof of overburden 18. Such coal pillar 10 supports a portion of the roof 18 between pillars.

If a reasonable yield of coal is to be expected when mining the thick coal seam 12 in this manner, the coal pillars, such as coal pillar 10, cannot be overly wide themselves, since the coal left in the pillars reduces the overall yield in the mining operations. However, if the width of each pillar 10 is kept down so that a high yield is possible, then breakdown of the pillars occurs as shown in FIGS. lb-ld. As shown in FIGS. 1b and 1c, due to the stress on the pillar 10, slabs of coal 20 eventually burst off the pillar 10, causing a coning effect. Such coning effect eventually results in pillar 10 weakening to the point where the immediate roof area of roof 18 supported by pillar 10 collapses (FIG. 1d).

The mining of a thick coal seam 30 under a roof 32 by use of the present method is shown in FIGS. 2a-2g. Initially (FIG. 2a), a top layer 34 of the coal seam 30 is removed immediately below and along the roof 32, leaving coal pillars, as coal pillar 36, which extends from the upper surface 38 of the remaining coal seam 30 to the roof 32 to support the roof 32. (It will be understood that a plurality of coal pillars are actually left to support the roof, and that the method disclosed, while being described in relation to a single coal pillar 36, applies to each of these other coal pillars not shown). The bottom portion 36A of the coal pillar 36 is then wrapped with a wrapping member 40 (FIG. 2b). .Such wrapping member 40 may with advantage be chain link fence material or wire rope which is tensioned while wrapping, and then released from tension after wrapping, whereby the bottom portion 36A of the coal pillar 36 is tightly wrapped. Or, the wrapping member may be a metal member applied in expanded form, and then contracted to provide a tight wrapping. The resulting wrapped coal pillar 42 is then coated over its entire surface with a seal coat 44 (FIG. 2c), which may with advantage be gunite, latex base spray, or shot crete. Such wrapping and coating serves to reinforce the coal pillar 36, providing a reinforced coal pillar 46.

A next layer 48 of coal is removed immediately below the removed top layer, meanwhile leaving the reinforced coal pillar 46 and a downward coal pillar extension 50 thereof. The resulting pillar 52 extends from the upper surface 54 of the remaining coal seam 30 to the roof 32 to support the roof 32 (FIG. 2d). The entire coal pillar extension 50 is wrapped with a wrapping member 56 as previously described, and the entire wrapped coal pillar extension is coated with a seal coat 58, also as previously described (FIG. 2e). Such wrapping and coating serve to reinforce the coal pillar extension 50, providing a reinforced coal pillar extension 60.

A next layer 62 of coal is removed immediately below the preceding removed layer, meanwhile leaving the reinforced coal pillar 46, reinforced coal pillar extension 60, and an additional downward coal pillar extension 64. The resulting pillar 66, made up of reinforced coal pillar 46, reinforced coal pillar extension 60, and additional downward coal pillar extension 64, extends from the upper surface 68 of the remaining coal seam 30 to the roof 32 to support the roof 32 (FIG. 2 The additional downward coal pillar extension 64 is then coated with a seal coat 70, as previously described.

It will be understood that additional layers of coal may be mined, if desired, with similar steps being taken to reinforce the pillars which support the roof 32.

It has been found that such reinforcement by wrapping and coating should take place as early as possible to inhibit relaxation and to cause the coal and reinforcement to begin working as a composite structure. Such wrapping and coating protects the skin or surface of the pillars from weathering, slabbing or bursting. In this way, thinner pillars can be used than in the prior art. Meanwhile, because of such reinforcing, it is ensured that the pillars will not break down under load, and will support the overburden or roof properly.

I claim:

1. A method of mining coal from a seam beneath a roof comprising:

(a) removing a top layer of coal while leaving coal pillars which extend from the upper surface of the remaining coal seam to the roof to support the roof;

(b) reinforcing at least some of the coal pillars; and

(c) removing a next layer of coal immediately below the removed top layer while leaving the reinforced coal pillars and downward coal pillar extensions thereof, the resulting pillars extending from the upper surface of the remaining coal seam to the roof to support the roof.

2. A method of mining coal from a seam beneath a roof comprising:

(b) wrapping at least a portion of each coal pillar with a wrapping member;

() coating at least a portion of each coal pillar with a seal coat, said wrapping and coating serving to reinforce the coal pillars;

(d) removing a next layer of coal immediately below the removed top layer while leaving the reinforced coal pillars and downward coal pillar extensions thereof, the resulting pillars extending from the upper surface of the remaining coal seam to the roof 5() to support the roof.

3. A method according to claim 2 wherein the wrapping member is tensioned while wrapping, and released from tension after wrapping, whereby the wrapped portion of each pillar is tightly wrapped.

4. A method according to claim 3 wherein the entire surface of each Wrapped coal pillar is coated with a seal coat.

5. A method of mining coal from a seam beneath a roof com-prising:

(at) removing a top layer of coal immediately below and along the roof while leaving coal pillars which extend from the upper surface of the remaining coal seam to the roof to support the roof;

(b) wrapping the bottom portion of each coal pillar with a wrapping member;

(0) coating the entire surface of each wrapped coal pillar with a seal coat, said wrapping and coating serving to reinforce the coal pillar;

(d) removing a next layer of coal immediately below the removed top layer while leaving the reinforced coal pillars and downward coal pillar extensions thereof, the resulting pillars extending from the upper surface of the remaining coal seam to the roof to support the roof;

(e) wrapping each entire coal pillar extension with a wrapping member;

(f) coating the entire surface of each wrapped coal pillar extension, said wrapping and coating serving to reinforce the coal pillar extension; and

(g) removing a next layer of coal immediately below the preceding removed layer while leaving the reinforced coal pillars and reinforced coal pillar extensiOns and additional downward coal pillar extensions thereof, the resulting pillars extending from the upper surface of the remaining coal seam to the roof to support the roof.

References Cited UNITED STATES PATENTS 2,191,248 2/ 1940 Cappel 6154 2,470,149 5/ 1949 Derby 61----54 2,846,205 8/1958 Bucky 2991 1 FOREIGN PATENTS 435,067 9/1935 Great Britain.

ERNEST R. PURSER, Primary Examiner US. Cl. X.R.