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Suggested Methods for Closing Mine Openings

Four general types of mine openings are present in the Kansas part of the Tri-State mining district: many vertical, square shafts; numerous larger vertical, rectangular, production or hoist shafts; a few horizontal adits; and a number of large areas of roof cave-ins.

Methods and materials are suggested to close or secure the openings in such a manner that they can be reopened, if necessary. It is recommended that shafts not be filled without plugs unless they are small, dry, and fill material is readily available nearby. Chert tailings are a dwindling resource which should be utilized in the best possible manner. The methods described are designed to be simple and to use a minimum of construction material (concrete, reinforcing steel, etc.) and fill material.

In the late 1950's, in connection with improvement of U.S. 66 highway, one of the authors of this report, then an engineering geologist with the State Department of Transportation, devised a plan to blast down the roof of a small section of a mine that extended under the highway just south of the present municipal building in Galena.

A part of the roof had collapsed at the west end of the room and it was possible for the geologists to survey and map the location and volume of the room and estimate the roof thickness. This was necessary to know for bid purposes.

Under construction a small bulldozer pushed dumped fill into the room until clearance with the roof prevented further filling. This was done to reduce the distance that the roof would fall and cushioning it to reduce seismic vibrations. The roof was then drilled from the surface and shot down with a series of delays between the lines of holes to prevent vibration damage to adjacent buildings.

Another section of the mine extends under U.S. 66 under Owl Creek near the west city limits. It was decided not to attempt to blast it down because part of the room had an 80 foot floor-to-ceiling height. It was feared that the hydraulic ram effect of the falling rock might collapse mine openings off the project right-of-way. Instead, the section of the pavement over the mine was heavily reinforced to act as a bridge if the roof did collapse from traffic vibration.

In general, there are few other places where blasting could be used without incurring possible liability, and it is not recommended.

On another highway improvement project, immediately west of Baxter Springs, a 75 foot deep and 75 foot diameter cone-shaped collapse crater had formed over a vertical shaft extending into a large room at depth. The volume of the surficial material which had collapsed into the hole was not sufficient to fill the shaft and the volume of the void was not known. A sharply tapered pre-cast concrete pyramid was devised. The base dimension of the pyramid was larger than the shaft. The pyramid was guided down the sloping sides of the crater and then lodged in the shaft. The crater was then filled with chat. Little or no settlement has occurred in the approximately 20 years since filling. As stated later, this method is recommended for deeper cratered shafts.

Vertical shafts are the most numerous and, depending upon conditions at or near the surface, may be treated in two ways: If bedded rock is within a few feet of the surface, the loose gravel or soil can be cleared away to allow a precast, reinforced, concrete slab to be placed on the bedrock surface; the same method can be used for shafts with concrete collars in fair to good condition.

Cratered shafts with timbered cribbing or no cribbing can be plugged with an inverted pyramid of concrete, depending upon the shape of the opening at bedrock. The base or top of the pyramid is designed to overlap the opening by about one foot on all sides.

The nature and dimensions of most of the hazardous shafts below a depth of about 6 meters (20 feet) is difficult to determine by observation at the surface. Since most of these shafts are collapsed at the top to some extent, it is impossible to look directly down the shaft. Shafts may either (1) dead end in solid bedrock, (2) enter rooms of various vertical and lateral extents, or (3) be bridged by rock falls or concrete foundations pushed into the shaft after cessation of mining. In any of these three cases the shaft may be flooded with water to varying distances from the surface. A survey of shafts at depth either by direct observation or a remote television system may be useful to determine the best method of shaft closure. In case (1), backfilling would be recommended; in case (2), a concrete plug would be advised and the shaft survey would determine the size and shape of the plug needed to close off the shaft at solid bedrock; and in case (3), if the bridge is judged to be stable, the shaft may be backfilled; if not, plugging would be advised.

Concrete plugs may either be cast in place over the shaft opening or precast and lowered into place. The first method could be used in the Galena area. Here solid bedrock is generally close to the surface. Lightweight forms could be constructed and lowered into the shaft opening. Because of the potential hazard of driving heavy equipment in this area, cement could be pumped some distance from a cement truck, which would remain on stable ground, to the shaft opening. Precast plugs could be used in the Picher field around Baxter Springs and Treece and other areas where solid bedrock lies some distance below the surface and the placement and filling of forms would be difficult. A down-the-shaft survey would recommend the size of plug necessary and it could then be lowered in by crane. The ground in these areas, although collapsed in places, is judged to be more stable than the ground in Galena and could support heavy equipment. In either case, a portable conveyor belt should be used to place backfill so that loaded trucks do not approach or dump directly into the hole.

It is not necessary, and probably would be dangerous, to attempt to clear away loose material above bedrock because the tapered shape of the plug will tend to guide it into the hole where it will wedge tighter as backfill material is applied. Any minor settlement of backfill will act to increase the wedging action.

Adits, which are few in number, will have to be treated individually depending on the size and shape of the horizontal opening. A suggested method is to wedge concrete forms into the openings, leaving a door in the center to allow access to the back or mine side of the forms. Holes should be drilled into the rock walls, ceiling, and floors of the opening, and steel rebars grouted in to assure that the concrete is pinned to the sides of the opening. After concrete is poured and cured, and forms stripped, a steel door frame and a door fabricated of closely-spaced welded steel strap should be bolted into the opening. The door will allow access, if needed, and provide for ventilation and drainage. An appropriate "no-trespassing" or warning sign should be attached to the door.

Large collapse craters in urban areas or near roads, especially if filled with water, should be fenced with six-foot high heavy-duty steel cyclone-type fencing with barbed-wire canted out on the top. A gate should be installed for access. Appropriate warning signs should be attached and replaced promptly if removed or vandalized. The fences should be set back an appropriate distance from the edges of the hole to prevent its loss in case of future caving--distance to be judged by conditions of the walls and past observation.

Cratered areas away from roads in rural areas can be enclosed with well constructed barbed-wire fences and locked gates. "No-trespassing" and warning signs should be spaced every few hundred feet apart.

An alternate suggestion for the area north of City Hall in Galena might be to fence around the cluster of shafts and collapse craters and provide wooden-fenced walkways similar to those built by the U.S. Park Service among the mud pits and geysers in Yellowstone Park. Explanatory signs and pictures could be placed at intervals along the path. The area could be locked at night or when unattended.

An information center, in conjunction with the walkway, might be developed in City Hall which is closely adjacent. If entry to the informational walkway was through City Hall, some control to access would be possible.

Displays stressing the historical importance of the first mines in Kansas and the development of the Short Creek District, Galena, and Empire City should attract passing tourists and visitors on nearby U.S. 66.

It is probable that there still exist old photos, pictures, and maps of the exact area to the west of City Hall as well as representative photos and displays of other areas, mills, smelters, equipment, miners, and people of the area.

Displays of actual mining equipment, if available, and explanations of its use in conjunction with displays of the district's rocks and minerals would be very informational.

In addition to the historical displays, panels might be made to explain the Bureau of Mines reclamation project, its objective, and sponsors. Enlarged color photos and an automated slide show with explanatory sound tape could be inexpensively devised. The effect of this would be to show the area and the project in a positive manner to the general public.

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Kansas Geological Survey, Tri-state Mining Area
Comments to
Web version May 2004. Report from January 1983.