English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

of research in South Africa and several other coal-producing countries. However, it began receiving serious attention only after the Coalbrook disaster in 1960. The most important outcomes of the initial investigations were the groundbreaking research by Salamon and Munro (1967) that resulted in the well-known power formula for pillar strength, and the work by Bieniawski (1969) that resulted in a linear formula for strength. The former approach was based on empirical back-analysis of failed and stable pillar cases, and the latter on in situ strength tests on large specimens. The Salamon and Munro (1967) formula has been widely used in South Africa and even adapted for application to hard rock pillars by researchers such as Hedley and Grant (1972). At the time of the initial work by Salamon and Munro, there were only 27 failed pillar cases suitable for analysis. It was not possible at the time to determine siteor seam-specific strength, and the result was a general formula for use in all seams in all mining districts. Since that time pillars have continued to fail and the database continued to grow – as of 2013, there were 85 cases in the database. Using the additional data, there have been a number of re-evaluations of the strength formula and it has also become possible to differentiate between the different mining seams and areas. The strength formula is used in conjunction with reasonable estimates of the pillar load to arrive at a safety factor. There are norms in place for safety factors for different purposes, such as short-term coal production panels, longer term main development, protection of overlying surface structures, etc. However, these norms are based on subjective judgement and the measure of stability cannot be quantified. Pillars with higher safety factors are logically ’more stable’ than those with lower safety factors, but ’how much more’ cannot be determined. The solution to this dilemma is to base design not on a safety factor, but on a probability of failure. The original Salamon and Munro (1967) work did give an indication of the expected probability of having a stable layout for any given safety factor, but as that was based on the characteristics of the database of failed pillars only, it was not strictly correct. This has been rectified by later work (van der Merwe and Mathey, 2013a) in which the probability of failure was determined based on a comparison of the number of failed cases to stable ones on a safety factor by safety factor basis. All the empirical work making use of databases of failed pillars has the same fundamental flaw: it is based on the as-mined dimensions of pillars (sometimes even the planned dimensions) and ignores the fact that pillars are known to scale over time. Consequently, the pillar dimensions at the time of failure cannot be the same as they were at the time of mining, and the safety factors will also not be the same. It can be argued that the stable pillars also undergo sidewall scaling and A three-tier method of stability evaluation for coal mines in the Witbank and Highveld coalfields