In underground coal mining, there is often a need for supplemental support for mine openings In the past, one of the most common types of supplemental support was wooden posts that were installed against the roof using opposing wooden wedges. Underground, wood has the tendency to shrink from moisture loss and dislodge if not under load Another drawback to using wood is the variability in strength between posts. Defects in the wood such as knots can cause weaknesses that often lead to premature failure of supplemental support.Many mines that install large amounts of supplemental support in certain areas of the mine such as bleeder entries in longwall mining have switched to using steel props rather than wood posts or cribbing. The reactions of steel props under loading are well-defined and there is little variability in strength between props. Steel props and can be fabricated so they can be used in a variety of roof heights without modification. Wooden posts often have to be cut to a usable length underground before installation. This adds to the installation time of the wooden posts. Steel props are more compact and can be lighter than their wooden counterparts, depending on the length and carrying capacity. Often times it is desirable to prestress the supplemental support to improve roof stability. This is often problematic and time consuming with some types of supplemental support.With these factors in mind, research was undertaken at Southern Illinois University Carbondale (SIUC) to design a new steel roof prop Several new clamping designs were developed and prototypes were fabricated and tested in the labs at SIUC in the spring of 2003. The designs were modified and refined and the first full-size prototype roof prop was tested in Ianuary 2004 With the success of the full-size prototypes, a cooperative research program was established between SIUC and Excel Mining Systems, Inc to further develop the new prop Development went smoothly and the prop has performed as expected.In February 2005, SIUC and Excel entered into an exclusive licensing agreement The prop design under license, the K-Prop, will be installed using a lightweight portable hydraulic jacking system under design that can be used to prestress the props, applying load to the roof and floor during installation By varyingthe installation load, the prestress load can be varied from about 1,000 to 10,000 pounds (4.448 to 44 48 kN) and at the same time, the carrying capacity of the K-Prop can be varied fiom 10,000 to 100,000 pounds (44 48 to 444 8 kN). The K- Prop is composed of only 3 pieces and laboratory testing has suggested that it can be installed by a pair of workers in less than two minutes. The speed of installation of the K-Prop should significantly reduce the total installed cost for supplemental support and should provide a safer working environment by prestressing the prop, which will add support load to the roof and floor during installation.
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