![]() As a rule, the difficulty of maintaining openings increases with depth, but even shallow workings at times encounter very heavy ground and may also be disturbed by rock bursts. Most large mines are deep, with many miles of drifts, raises, stopes, and shafts with open spaces more or less loosely supported by rock pillars, fill, and timber or other material, or by a combination of such supports. Essentially, the difference lies in the depth and in the extent to which the two types of work are compared. Support of underground openings is much the same for both large and small mining operations. Similarly, a higher working stress for timber is also suggested, as are standards in working stresses for concrete, steel, and timber in mine-support design that are different from those used for surface structures.Īlthough headframes and ore bins are not a part of mine support, most mine plants find them necessary for this reason information on these two surface structures is also included. ![]() Designing these sets by ultimate strength procedure is discussed in some detail. Several drawings and designs are offered for actual dimensioning and design of chutes for limited tonnage operations, which has been inadequately presented in the past.įor areas where timber is scarce or expensive, reinforced concrete sets of simple design should be substituted. Also the advantage of replacing collapsed headboards or blocking before failure of the main support is discussed. Then, because rock bolts are in wide use today for replacing or supplementing timber, their use and installation are extensively outlined. Another subject introduced is treatment of timber for prolonging its life, which, on occasion, should be considered even by the modest operator. Drawings and sketches are used to show various timber sets and methods of erecting and blocking them and the accompanying text includes pertinent supplementary remarks. And because small mine operators may not be aware of the importance of properly blocking timber sets in place, this frequently slighted but important aspect of the supporting process is discussed. This Bulletin presents discussion and sketches as a guide for designing underground support of timber, concrete, or steel in relatively shallow workings.īecause timber will satisfy most support requirements, this discussion offers methods for supporting drifts, raises, shafts, and stopes, as well as suggestions for framing and later transporting packaged units into the mine. No matter how limited their extent, few underground mining operations progress very far without requiring some sort of support.
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