Borehole aerostatic ground support system

#Our invention is a method and apparatus to provide support and stabilization to an underground mine.

#Within the mining field underground support has been provided by inflatable flexible containers of various shapes and sizes. A good explanation of some of these prior art containers can be found in the U.S. Pat. No. 2,990,166 to M. A. Walsh. As shown in FIGS. 1 and 2 of the Walsh patent, the proper support is provided when the inflated containers span the roof to floor and come into bearing contact with them (column 4, lines 5-14). One of the disadvantages with these types of supports is that they provide immediate support only to the mine bearing surfaces in contact therewith and perhaps a small adjacent roof area. Thus, in auger mining where the boreholes may easily be 100 or more feet in length and around 18 to 60 inches in diameter an exceedingly large and expensive inflatable support would have to be provided to fill the borehole cavity.

#Another method that has been used in the past to support the overburden, especially in the tunnelling art, is that referred to as the plenum process or compressed-air method. The book entitled "Practical Tunnel Driving," by Harold Richardson and Robert S. Mayo -- 1975 McGraw Hill Book Co. (1st Edition 1941) on pages 275-300 describe this method as does the book "Tunnels and Tunnelling" edited by C. A. Pequignot, Hutchinson and Co., Ltd., London (1963), pages 158 to 184. Essentially what this method does is to provide compressed air to a tunnel lining which has been locked off from the free air side to allow the working face area to be under air pressure. Depending on such variables as the ambient materials making up the tunnel, the depth below water level, and the safety considerations for the workers, the pressure and amount of compressed air is determined and controlled to prevent the water and surrounding material from collasping on the workers or from exploding outwardly towards the water's surface.

#FIG. 1 schematically illustrates the preferred embodiment of our invention in a cross-sectional view with one container or two containers (in phantom lines) in situ within a mine borehole.

#FIG. 2 shows a typical auger-mining operation employing our invention.

#FIG. 3 depicts in cross-sectional view a panel auger-mining system employing our invention wherein an auger hole is bored through a coal panel.

#As shown in FIG. 1, the inflatable enlongated first container 1 is inflated and in situ within the underground mine borehole 3. To the right of the container is the borehole's deadend cavity which may be created by the natural end of the hole or by plugging the free end of the open hole by another inflatable container similar to the first. When so placed, these containers provide support for the borehole overburden 5 immediately above it and more importantly, seal the borehole for later pressurization. Extending the total length of the container through its centerline is the fluid conduit 7. This conduit receives its input of compressed fluid, usually air through a tubular hose 10, from a compressor or pump located to the left. To control the amount of fluid entering the conduit via manifold coupling 9, a conventional valve 17 with its external handle is employed in conjunction with the fluid pressure meter 11. Inflatable container 1 is filled through valve 13 from the same coupling 9 and fluid pressure source. Pressure meter 15 acts in conjunction therewith to accurately indicate the amount of pressure in the container.

#At far end of the conduit--to the right--is the quick connect coupling 19 which may allow a second inflatable container 21 with a through conduit 23 (shown in phantom lines) to be connected in fluid communication in seriatim with container 1. Connecting two containers in series would increase the safety factor. Either container by itself would be capable of containing the pressurized borehole fluid. Thus the chances of a major blowout would be reduced should either container rupture. This second container is similar to the first described. It would have an input valve 25 and meter 27 like valve 17 and meter 11 so that it could be filled via conduit 29 independently of the fluid being sent to the borehole cavity.

#Initially, compressed fluid is inputted past control valve 13 and pressure meter 15 so that it exits into the container 1. After this container is inflated to a predetermined pressure level, it forms a fluid tight borehole plug. Assuming this is the only container, valve 17 is then opened to allow the pressurized fluid to enter the borehole cavity to the right of the container. Upon entering this cavity the fluid begins to increase the pressure level therein until it is filled and a predetermined pressure level achieved. Once the fluid pressure levels in the first container and the borehole cavity have been achieved, they are maintained as long as desired to give the needed overburden support. When it is desired to remove the container and allow the borehole to collapse, the fluid pressure is simply reduced and the container removed. In an actual working arrangement, we contemplate many of these containers with at least one in separate different boreholes as shown in FIG. 2. By systematically allowing their pressure to be reduced and removing them, it is possible to cause a large mine section to collapse under the weight of its overburden in a controlled manner.