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History of Wooden Support

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Rock support is the term widely used to describe the procedures and materials used to improve the stability and maintain the load bearing capacity of rock near to the boundaries of an underground excavation. In this paper, we will discuss about active support, particularly wooden support where the supporting elements are an integral part of the reinforced rock mass, and rock support, where the supporting members are external to the rock and respond to inward movement of the rock surrounding the excavation. A critical safety component for all underground mining is intrinsic and standing support. Specifically, tabular hard rock mining exploits a wide variety of deposits that require various methodologies to safely mine the ore material.

History of wooden support

wooden supports begun before the industrial revolution. This created a high demand for timber, for which the mines were often competing with the smelting plants. The basic support system used was called a 'square timber set support' where there were two vertical supports and one horizontal on top of them. The area above the supports was covered with wood and often filled with waste rock. The vertical and horizontal supports were joined together using different methods, depending on which direction the main pressure was coming from, the side or the ceiling. In areas of low structural stability or in areas where the rock had been disturbed by prior mining, the supports were placed right next to each other, as can be seen in the midsection of the Johannes mine shaft, where the rock structure had been disturbed by open air mining.

In more advanced stages of mining, wood was also used to construct fake ceilings as mining often took place on various levels, depending on where the minerals were located. The supports often had to be repaired, but once the mine had been abandoned and began to rot, and in places close to the surface or in large chambers where the rock was unstable, the mine would often collapse and cavein. The open pit mines and the entrance mine shafts were kept in good technical condition over a long period of time as they were used to transport mined ore and drain the groundwater.

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Wooden support is often referred to as timber support. Wood is the traditional supporting material used in mines. Softwoods (spruce, fir), sometimes hardwood (oak) are mostly used for support purpose. a timber with a long fibre structure is always employed, such as spruce, fir, or other conifer wood, or eucalyptus. Timbers of these wood types shatter slowly when their loading capacity is exceeded and thus warn the miners through a definite creaking. Short-fibered timbers break without any prior, slowly-developing visible or audible indications. A dense, resinous, slow-growing wood type is always preferable for mine support purposes.

Timber support normally is not reusable. The only exception is simple prop timbering for stoping which is sometimes recovered, and the wood then reused for shorter props, head boards, breast timbers or wooden cribbing. In situations requiring excessive support, such as mining in incompetent rock, the cost off timbering becomes a significant factor in the economic analysis of the operation. Here the higher investment costs for friction prop support can result in a substantial savings in operation costs, since these support elements can be reused.

Most wooden support systems have a finite amount of energy that can absorbed during deformation. Based on laboratory tests, pack support systems appear to have a continually increasing deformation. However, it is estimated, that the useful energy absorption ability of pack support systems is limited about 50% compression, since most pack types clearly do lose structural integrity after large deformations in underground conditions, particularly under dynamic closure.


Timber-Elongated based support

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The large family of elongate support units, introduced in the gold and platinum mines over the years, was developed to accommodate stope closure rates in excess of those tolerable by normal timber props. Yield capabilities of 200mm to over 400mm are typical. These systems are used predominantly in medium to deep stopes where the rockburst potential is moderate. However, they also find application in shallow stopes where the rates of closure are abnormally high for these depths.

The main function of elongate support system is to prevent rockfalls in stopes where the hanging wall is highly fractured, and the closure rates are moderate to high. Nevertheless, they are also required to contain rockburst damage.

Pack Support Systems[pic 8]

A large variety of pack types are available, with widely diverse load deformation characteristics. The options range from relatively soft and weak skeletons packs, through mat and solid packs, combinations of concrete blocks and timber, grout packs with the grout gravitated from a surface preparation plant, combination of elongates and framework of timber slabs, to the more recent innovations of end grained timber blocks with with parallel grained slabs and lightweight foamed concrete, reinforced with either annealed steel mesh or wood fibres. These layer two types are supplied in modular sections, which interlock and can be engineered to provide a wide range of combinations of initial stiffness, yield force and strength. Thus, the challenge to the design engineer is to define the support requirements and then choose the appropriate pack type to match the requirements in the most cost-effective support system

Packs are used as panel support in many geotechnical conditions and almost universally, except in some shallow platinum mine stopes, as gully support. They comprise about 60% of support used in gold mine stopes but play a relatively minor role in platinum mines where stiff low yield ability support is generally required. The characteristics of packs, which account for their widespread usage are: high strength, at least 50% yield ability in most cases, structural integrity when subjected to eccentric loading and relatively large direct area coverage compared to prop types.



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