Mine Support

a man-made structure erected in mines to prevent caveins and heaving of the surrounding rock, to preserve the required dimensions of the mine cross section, and to absorb and control rock pressure. Mine support must provide mine safety and be economical, portable, and simple to maintain, neither interfering with nor complicating the conduct of production processes.

Mine support for main and developmental workings is classified according to the support material, according to the nature of the structure (rigid, yielding, articulated, or mixed support), according to service life (permanent or temporary support), according to the type of mine cross section (trapeziform, arched [open or closed], annular, elliptical, or polygonal), and according to the type of working (flat, inclined, or vertical faces).

Cast concrete and reinforced-concrete support, prefabricated metal and reinforced-concrete support (tubing), and steel frame support are used in main workings (shafts, shaft-bottom workings, tunnels, main crosscuts, and chambers) with a long service life. Circular cast concrete-block support is a solid-walled cylinder whose outer surface is flush with the surrounding rock, with a wall thickness of 20-25 cm or more, depending on the magnitude of the rock pressure and the diameter of the working. Arched cast concrete-block support is used in horizontal and sloping workings (to 30-35°) for average stability and with strong (nonheaving) rock in the soil. When peripheral pressure is present, the walls of the arched support are made curvilinear. Cast reinforced-concrete support differs from a cast concrete-block support by the presence of reinforcement, which may be flexible (made of steel rods) or rigid (made of metal beams) and which withstand the tensile forces from considerable and nonuniformly distributed rock pressure.

Prefabricated reinforced-concrete supports are also used in horizontal main workings together with cast concrete-block sup-ports. They include solid tubing, arched, annular, or elliptical supports. Rigid supports that withstand loads within the limits of elastic deformations with no change in the shape or dimensions of the support or working are usually used in main workings.

Articulated yielding steel arches and rings are the most common kinds of supports for reinforcing developmental workings. The dimensions of yielding supports may be reduced by the effect of rock pressure, so that the dimensions of the shaft may also be reduced as a result of displacement or deformation of the elements, with preservation of the supporting power and durability of the structure. Elements of yielding metal frames are made from the specific profile and are joined together at lap joints by means of clamps and bolts. The yielding quality of the support is achieved by slippage of the elements at the joints. Mixed frame supports consist of hollow tubular and rectangular reinforced concrete props and steel bars joined by means of a suspension hitch. Roof bolting is used independently, particularly in the ore-mining industry, in conjunction with frame supports. Rigid trapeziform, arched, and annular steel supports made of I-beams and rails, with the elements joined by hitches and nuts and bolts and, less frequently, by means of special clips, are also used (mainly in ore shafts). The support frames are usually set up 0.5-1.0 m apart. The roof and wall between the frames are enclosed by lagging—reinforced-concrete slabs, metal grates, and various kinds of metal screens, planks, and half-round timbers.

Wooden frame support (including half-round timbers) is used mainly in mines of small cross section and short service life (up to 3-5 years). Mines with a long service life are usually rein-forced with fire-resistant materials (metal, concrete, and so on). Trapeziform frames are usually installed 0.5-1.0 m apart, with the roof and walls of the shaft between frames reinforced by half-round timbers, or close together. Closed (four-section) supports with a floor bar are used if the soil exerts pressure on the mine. Square timber supports constructed in vertical and sloping development faces (greater than 45°) of small cross section (test holes, blind shafts, headings, and crosscuts) may be solid, when the barring sets are installed on one another, or with props, when props 0.5-2.0 m long are mounted between the barring sets. The barring sets are made of round or squared timbers and are connected with double-notched joints, and barring sets are usually connected to props by slot joints.

Support for the broken working area is designed to reinforce the face section of broken workings where equipment is located and where mineral extraction operations are conducted. This type of support is made in the form of frames consisting of steel or wooden props and roof bars, a so-called individual support. The frames are arranged in regular rows along the working face and drift as the face advances. The support installation patterns are different for gently sloping and steep coal seams. The most advanced type of support, a movable powered support, has become widespread in modern working faces (longwalls) of coal mines. Special waste-edge supports are used in broken working for roof control (using rock pressure).

Mine support structures for main and development workings are being developed through a reduction in the consumption of materials per unit of supporting power of the support, through the use of polymer materials, and through the building of prefabricated sectional and standard reusable supports and of movable powered supports for joining development workings to the working face, temporary supports for entry faces, roof bolting fastened with polymer resins and quick-setting inorganic binders in cartridge form, and screw anchors.