African Mining July - August 2019 | Page 44

Operations structural properties and being a renewable resource. “Timber remains a cost- effective and reliable material for mining applications and still forms a crucial part of the mining support systems,” she says. Going forward, De Haas says that the demand for timber in the mining industry will depend largely on how effectively timber can compete with other products. “Timber is a renewable resource, unlike any other support material used in mines.” Advantages and disadvantages of using timber in the mining industry Timber planks stacked neatly ready to be used. entries, and along haulage corridors,’ the article explains. mine roof by spanning two parallel mining props,’ the article states. Next it describes sawn props, which have a similar purpose to round props. The difference is that they have more of a permanent function in that they are often set in mine corridors for up to 10 years. They are also the main preference for mines because they are simple to use. When explaining the split props, the article mentioned that they would normally conform to the same standards as round props. Depending on the original diameter, spilt props are halved or quartered. This makes them versatile enough to be used for other functions such as wheel chocking and lagging. According to the three authors, lagging is described as having similar dimensions to planks which are used for shoring sides of mine entries, shafts and haulage ways. Lagging can be stacked in two ways: lengthwise or crosswise on top of crossbars for roof support. The article also mentions that it is possible to rehabilitate some wood products for other uses as well. For example, ties can be used for railway support, but also provide a large bearing surface against a soft or muddy surface. In addition, after being rehabilitated, ties can also be sawn and sacked similar to crib blocks and be used for pillar support. Another category of timber product is a header which functions as a bearing surface against mine roofs. Also known as caps, headers are ‘conventionally mounted in props to fill gaps and tighten the wood structure into the mine roof ’. The article highlights that headers can be replaced by metal. According to De Haas, Merensky Timber has seen a steady decrease in mining timber demand over the years, with volumes reducing further as a result of numerous shaft closures. “Mining timber is expected to decrease in line with the decrease in demand from mines. Price increases are expected to be inflationary, but also linked to the demand for other timber uses,” she adds. Some timber products serve more of a support function and are used together with other timber products. Crossbars are an example of supporting timber products, where they are usually used along with props and headers. ‘They help support the 42 AFRICAN MINING JULY - AUGUST 2019 The last timber product described by the journal is a wedge which is described as a pie-shaped wood slab. Typically, the slabs are sawn at the mill and then wedged on top of headers to tighten the props to the mine roof. ‘Coal mines keep a large supply of wedges on hand since they can be used for any purpose requiring tightening or blocking of a support structure,’ the article says. The future of timber use in mining Although timber in mining continues to face various challenges, De Haas maintains that the use of timber in the mining industry is still prevalent due to its unique Advantages: Timber is cost-effective for use in the mining industry. The high density of eucalyptus makes it a strong, durable and structurally-sound product. As a construction material, mining timber requires none of the special equipment needed for placing concrete or steel supports.  Another key advantage of timber over other support-system materials is the safety factor. When crushed by extreme pressure, timber collapses slowly and not suddenly like concrete or other materials. Timber is a renewable resource, unlike most other support materials used in mines. All support materials consume energy and other resources in their creation, construction and eventual demolition. At each stage, this consumption can have a significant impact on the environment at global, regional and local levels. Using environmentally sustainable support materials like timber helps reduce the use of fossil fuel energy and minimises adverse environmental impacts. Disadvantages: Timber is considered more of a fire hazard than some other support materials, although it retains its structural strength at high temperatures while it is burning. Timber can shrink, swell, twist and crack over time, although Merensky has for decades been involved in breeding eucalyptus species that are less prone to wood end-splitting and thus deliver greater strength. b Merensky Timber www.africanmining.co.za