Mining method

Abstract

A mining method includes removing material to be mined from one wall of a mine, and spraying a foam of plastic, polystyrene, polyurethane, or cement onto an opposite wall to continuously fill the mined cavity, except for the required immediate working area of the mining machinery. The foam controls roof fall and earth subsidence into the mined area and obviates the need for temporary roof support apparatuses and the required attending and maintaining personnel. Since the foam entirely replaces the mined material and provides its own roof support, the entire deposit area can be safely and efficiently mined.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to mining methods and more particularly to improvements in methods for controlling roof fall, subsidence, and the like.

2. Description of the Prior Art

In mining, especially for coal deposits or the like, normally one or more access tunnels or entries are cut into the seam or deposit to be mined. In one commonly used method, called the longwall method, a plow, shearer, or other such mining apparatus is driven or towed along one wall of an opening in the coal seam or face between the access tunnels to cut into and remove a portion of the wall of the opening, creating a new face at the depth cut. The product cut is removed from the mine by a conveyor or other means, and the process is repeated successively cutting away the wall until the plow has been moved the required distance into the deposit. As the cavity from where the mined product has been removed becomes large, the roof begins to crumble and fall into the mine. Usually a number of roof support apparatuses are employed to control this falling in the immediate area of the plow. The mine roof away from the plow, however, is ordinarily allowed to fall directly into the mined cavity. Thus, each time the plow removes portions of the wall, the roof supports and the conveyor or other removal means are moved towards the new wall or face, and the roof in the direction away from that of the plow progression crumbles into the mined out seam.

Over a period of time, the earth to its surface above the mine sinks or subsides into the voids created by the removal of the subsurface mined product. In many instances controlling the amount of subsidence is desirable or necessary, for example, in mining under a river the course of which may be changed by subsidence of the land areas adjacent its bed.

Because of the requirements for moving the roof support and the product removing conveyors each time the mine wall is cut, commonly a large number of underground workmen are needed, for instance, one workman to attend a specified number, such as 10, of the roof supports. Such underground work is difficult, heavy and dangerous, and is found undesirable by many mine workers. Such extra men and equipment also constitutes a direct expense of the mining operations.

Another problem encountered in present mining methods is the low extraction ratio with which the product to be mined can be removed. Typically the extraction ratio of present methods is on the order of 50 percent or less. This is because once a horizontal cavity has been mined, the roof fall in the mined area precludes subsequent mining at levels above or below the presently mined cavity, without extensive artificial support. Such support is provided, for instance, for a lower level mining effort by allowing a particular ceiling thickness between the previous mined cavity and the area to be mined, together, perhaps, with support columns or pillars in the lower mine. Also, often large pillars of coal or mine product are left to prevent caving in active mining areas.

The obtainable ceiling height or seam thickness is another factor in the extraction ratio since less than all of the material desired to be mined can be removed. Ideally, the seam thickness should be as large as possible to remove as much mine material as possible. However, there is a practical limit on the height at which the ceiling or roof supports can be safely utilized. For increased height, larger and harder to manage and move supports are required, which need more attending personnel and take more time to move.

A hazard which should be considered, especially in coal mining operations, is that poisonous or noxious fumes, explosive dusts, and the like, are often generated in the mining processes. Such fumes, dust, and the like, must be controlled or removed from the mine to prevent injury to the mine workers. Ventillation techniques used to control such fumes and dust typically employ systems which are expensive to maintain and operate, and which require elaborate stope planning to provide proper air flow paths.

SUMMARY OF THE INVENTION

In light of the above, it is, therefore, an object of the invention to provide a method for underground mining. It is another object of the invention to provide a method for supporting the roof of a mine or the like. It is still another object of the invention to present a method for controlling subsidence of overlying earth into an underground mine. It is another object of the invention to present a method for increasing mine safety. It is yet another object of the invention to present a mining method which can be remotely controlled. It is still another object of the invention to present a method for underground mining with increased production efficiency. It is still another object of the invention to provide a method for underground mining of very thick seams.

These and other objects, features, and advantages will become apparent to those skilled in the art from the following detailed description, when read in conjunction with the appended claims and accompanying drawing.

In accordance with the invention, a mining method is presented in which the product to be mined is removed from a mine wall. As the removal of the mined product progresses, a supporting foam material is deposited onto an oppoisite wall. The foam essentially fills the mined area, except as required for the operation of the mining equipment. The preferred foams are of plastic, such as polystyrene, polyurethane, or the like, or foam cement, or the like, to support the ceiling and, where required, to control the subsidence of the overlying earth. The compressive strength of the foam may be determined in accordance with the desired degree of subsidence control -- the deeper the mine, the greater the compressive strength of the foam for an equal degree of subsidence control.

BRIEF DESCRIPTION OF THE DRAWING

The invention is illustrated in the accompanying drawing wherein:

FIG. 1 is a top view of a mine panel cut away to show the entries and coal face and the mining apparatus therein, in accordance with the invention;

FIG. 2 is a cross-sectional side view of the coal face taken at 2--2 in FIG. 1 showing the mining apparatus in accordance with the invention after one wall has been cut and the other wall sprayed with foam;

FIG. 3 is a cross-sectional side view of the coal face taken at 3--3 in FIG. 1 showing the sprayer apparatus of the invention after cutting one wall out prior to the deposit of foam onto the other wall; and

FIG. 4 is a cross-sectional side view of the coal face taken at 4--4 in FIG. 1 prior to cutting.

In the figures of the drawing, various parts have been exaggerated in size or dimensions for clarity of illustration and ease of description. Also, like reference numerals are used to denote like or similar parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the FIGS. 1-4 of the accompanying drawing, a mine panel in which the method of the invention can be practiced includes access haulways 10 and 11 at each end of an area 12 to be mined. In accordance with well-known "longwall" mining methods, the material in the area 12 to be mined is continuously cut and removed from a wall 13 by a plow, blade, or shearer 14. The removed product is directed by the shearer 14 onto a conveyor 15, typically a chain conveyor, for removal from the mine. The shearer 14 is carried on top of the chain conveyor 15 and is towed by a cable 21 drawn by powered reels 22 and 23.

In accordance with the invention, foam plastic or other foam material is sprayed, blown, or otherwise deposited onto a wall 24 opposite that on which the shearer 14 cuts, to fill the mined cavity 25 with the foam material. To effect this foam deposit, two sets of nozzles 31 selectable to be generally aimed rearwardly to this direction of travel are provided on a mixer assembly 32 by which the foam plastic is mixed and sprayed onto the roof and opposite wall 24. The mixer assembly 32 rides upon the conveyor 15 and is towed a desired distance behind the shearer 14 by cable 40 between powered reels 42 and 43. Alternatively, the mixer assembly 32 can be tied directly to the shearer 14 by a cable, chain, or the like (not shown) to be towed by the shearer 14 the desired distance therebehind. The ingredients for making the foam plastic mix are conducted under pressure from tanks (not shown) on the surface or other convenient location, in one or more hoses, such as hoses 33 and 34, illustrated, to the mixer assembly 32 and the selected nozzles 31.

To protect the hoses 33 and 34 from damage by dragging on the mine floor, a trough or channel 36 is provided on the conveyor 15 on which the mixer 32 rides. The hoses 32 and 34 can also be wound on respective reels 44 and 45, to be unwound or wound, as necessary, as the mixer assembly 32 is moved along the conveyor 15.

Thus, in operation, the shearer 14 is towed from one haulway 11 to the other haulway 10, cutting material from the wall face 13 and directing it onto the conveyor 15 for removal. The chemical mixer 32 is drawn along the opposite side of the conveyor 15 at a trailing distance of several feet, to spray foam, filling the mined area 25. Because the foam is directed onto the ceiling (See FIG. 2) as well as the opposite wall, no roof support apparatuses are needed. As the cutting and removal of the mined material continues, the conveyor 15 and the shearer 14 and mixing assembly 32 are moved toward the new face 19 cut by the shearer 14 by rollers 47 and 48 on the mixer assembly 32. The rollers 47 and 48 ride upon the foam previously deposited onto the opposite wall 24, so that the mixer assembly 32, riding in a fixed relationship at the side of the conveyor 15 pushes the conveyor against the newly cut face 19, as the mixer assembly 32 is towed behind the shearer 14. The rollers 47 and 48 additionally function to maintain the relative position of the shearer 14 to the face 13 to be cut.

When the shearer 14 and chemical mixer 32 reach the haulway 10, they are reversed in direction, cutting and spraying back to the haulway 11. The cable reels 22 and 23, and 42 and 43, as well as the hose reels 44 and 45 are advanced within their respective haulways 10 and 11 in the overall direction of advance of the shearer 14. The reels can be moved manually or by remote control, as desired.

When the directions of the shearer 14 and chemical mixer 32 are reversed, the mixer 32 again is towed the desired distance behind the direction of travel of the shearer 14. Additionally, since in the embodiment illustrated the foam plastic is sprayed behind the mixer 14, the foam is directed to the selected rearwardly aimed nozzels 31, and the operation continued. The process is continued until the entire area 12 to be mined has been removed. It can be seen that the method can be easily adapted to be remotely controlled to eliminate the need for equipment operators in the mine, since the only operation which needs to be performed is drawing the shearer and sprayer back and forth.

The chemicals conducted to the mixer 32 by the hoses 33 and 34, when combined, result in a foam material, such as polystyrene, polyurethane, foam cement, foam plastic, or the like being produced. By appropriate choice of materials, the foam sprayed onto the wall 24 can have practically any desired compressive strength. Of particular safety advantage is that by addition of appropriate additives, the foam can be made fire retardant. Examples of materials which can be used and their physical properties can be found in the Encyclopedia of Chemical Technology, 2nd Edition at page 860 and pages 864-867, which are incorporated herein by reference. Thus, the subsidence of the overlying earth can be controlled to practically any desired extent merely by regulating the compressive strength of the foam material. It is known, for example, that polyurethane can be made with a density of, for example, 8 pounds per cubic foot, which will be sufficient to adequately prevent the subsidence at a depth of approximately 200 feet and limit the extent of subsidence at even greater depths.

Thus, as the material 12 is removed from the mine and substituted with foam, it can be seen that since the wall areas opposite that being mined are sprayed with foam in a continuous process, the entire material within the panel can be effectively removed. Also, since the entire mined void is filled to the ceiling, the principal limit on the height or seam thickness is that of the size of the available shearer or cutter. Thus, since no roof supports are used the ceiling limit can be increased with increased extraction ratio, and the personnel previously required to attend the supports are not needed for that purpose.

If desired, the material cut from the wall 13 by the shearer 14 can be removed from the mine with pneumatic suction or vacuuming devices known in the art, not shown, such as by an apparatus similar to that described in Mining Congress Journal, Dec. 1971, pp. 42 et seg. Such suction or vacuum means is a desirable method of removing the cut material, especially in coal mining operations, since noxious methane gas liberated by mining the coal can be controlled as well as any other noxious gases which might be produced by the manufacture of the foam. Furthermore, such vacuuming or pneumatic apparatuses can sufficiently control the dust which may be produced in the mining operation which can create undesired explosive atmospheres. The density of the teeth on the cutter head may be designed to cut the mined material into a small enough size to facilitate transportation of the mined material in the suction pipes to the surface.

One particular advantage of the apparatus of the invention is that it can be operated remotely, for instance, from a central control room, without personnel at the actual cutting site. Additionally, the method is much more efficient than those heretofore since no supporting or separating walls need be provided for roof support. Furthermore, since each mined cavity is completely filled with the foam generated, it is possible to mine in layers; that is, mine a fist layer, go back and mine the next upper (or lower) layer and so forth.

Although the invention has been described and illustrated with a certain degree of particularity, it is understood that various modifications and changes in the apparatus and method may be employed without departing from the spirit and scope of the invention as hereinafter claimed.

Claims

What is claimed is:

1. A method for underground mining comprising advancing a cutting device along one longitudinal wall of a mine shaft to remove a mining product therefrom and substantially concurrently advancing a foam support material dispensing device within said shaft behind said cutting device and in the same direction to progressively fill at least a portion of the enlarged void of said shaft created by the removal of said mining product so as to control roof fall and subsidence of the overlaying earth.

2. A mining method comprising the steps of advancing a material-removing plow along a wall of a mine, substantially concurrently advancing an apparatus for spraying a supporting foam onto an opposite wall from that along which said plow is advanced, supplying the ingredients for making said supporting foam to said spraying apparatus, mixing said foam making ingredients, and spraying said mixed ingredients onto said opposite wall.

3. In a method for underground mining comprising removing a mining product from a wall of a mine shaft and substantially concurrently introducing within said shaft a foam support material adapted to at least partially fill the portion of said mine shaft enlarged by the removal of said product, the improvement comprising the steps of advancing continuously along said mine shaft from one end to the other an apparatus for cutting said mining product from said wall and a sprayer for depositing said foam support material and maintaining said sprayer at a constant distance behind said cutting apparatus.

4. A method as in claim 1 wherein the direction of motion of said sprayer and said cutting apparatus is periodically reversed.

5. A method as in claim 3 wherein the advancing of said cutting apparatus and said sprayer is accomplished by means controllable remotely from said shaft and wherein said cutting apparatus and said sprayer are each towed by means of at least one cable extending substantially through the length of said mine shaft.