Despite the increasing popularity of open-pit mining, underground mining remains to be the more efficient method, particularly when there are digging restrictions. For instance, when excavation has to be done in an area where there are surrounding structures, the pit must be small enough to avoid disturbing the integrity of the soil on which the structures are founded. Underground mining, however, entails the building of a shaft system.
A shaft system is the structure where materials and people are transported to and from the underground mine. It consists of metal frames that hold the earth and a conveyance system for miners and ore. Its diameter is measured based on the estimated volume of ore to be extracted and the size of workforce. Large shaft systems may have more than one mine cage and a set of intricately installed skips.
Excavation and Sinking Considerations
Considering the changing soil condition as excavation goes deeper, there are crucial factors mine shaft designers consider.
High Foundation Loads. The buildings and houses surrounding the mine site have often been in an undisturbed balance with the ground for a long time. A sudden deep excavation could disrupt that balance and result in collapse of those structures. In addition, as the site develops, heavy equipment and structure are expected to be built above ground. Concrete piles are driven into weak regions of the ground to ensure that loads won’t depress the soil and compromise the shaft’s stability. The shaft and its components therefore must be designed and built with the toughest materials to withstand inward pressure.
Groundwater and Rock Cracks. The edge of the shaft and its surroundings can be a high-traffic area. Groundwater pooling along this section may weaken the edge of the shaft. This is remedied by grouting to increase the elevation of the shaft’s edge to prevent water from flowing in, which helps keep the shaft, skips, and mine personnel cages dry.
Resistance to Friction, Tension, and Compression
Besides the inward pressure exerted by the soil, the shaft is also subjected to friction, tension, and compression created by the moving and stationary load within it. The mine cages and skips must be made of the toughest alloys of steel to withstand tension. This is to protect the passengers and reduce the stress passed on to them through each conveyance cycle.
Mine companies have to entrust the manufacture of shaft conveyances to reliable mine equipment manufacturers like Wabi Iron & Steel Corp. These companies follow the highest industry standards to ensure that their equipment perform well and last long, and employ highly skilled tradespeople. Engaging equipment manufacturers such as these will ensure the continuity and success of the mining operation.
Source:
Geotechnical Design Considerations For Mine Shafts, srk.com
Deep Thinking: Shaft Design and Safety for a New Generation of Mines, e-mj.com
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