this paper gives an overview of the difficulties associated with the design of hard rock pillars in south african mines. recent examples of large scale pillar collapses in south africa suggest that these were caused by weak partings which traversed the pillars. currently two different methods are used to determine the strength of pillars, namely, empirical equations derived from back analyses o...

This paper gives an overview of the difficulties associated with the design of hard rock pillars in South African mines. Recent examples of large scale pillar collapses in South Africa suggest that these were caused by weak partings which traversed the pillars. Currently two different methods are used to determine the strength of pillars, namely, empirical equations derived from back analyses o...

Several empirical equations to estimate coal pillar strength have been presented in academic studies. The development processes of these equations are similar and are usually obtained by fitting the mathematical function (curve) to field data. One of the best criteria to evaluate the quality of fitting for such equations is the correlation coefficient R2, which has limited applicability. It is ...

In some instances, extensive room-and-pillar workings can collapse with little warning and pose a serious risk to underground miners. Traditional strength-based pillar design methods applicable to coal or hard-rock mines use a factor of safety defined as pillar strength divided by pillar stress. Factor of stability, defined as local mine stiffness divided by post-failure pillar stiffness, may o...

Pillars with width-to-height ratios of less than 1.0 are frequently created in underground hard rock mines. The strength of slender pillars can be estimated using empirically developed equations. However, the equations can provide variable results when the width-to-height ratios approach 0.5. This paper investigates some of the issues affecting pillar strength at low width-to-height ratios in h...

We demonstrate strain-rate sensitivity emerging in single-crystalline Cu nanopillars with diameters ranging from 75 up to 500 nm through uniaxial deformation experiments performed at different constant strain rates. In the range of pillar diameters and strain rates tested, we find that the size dependence of the pillar strength deviates from the ubiquitously observed power law to a relatively s...

A recent experimental pillar extraction project at a UG2 bord-and-pillar mine presented unique opportunity to compile new database. Currently, the South African hard rock mines are designed using Hedley and Grant formula with modified K-value. This empirically derived was developed for uranium in Elliot Lake district of Canada. The use this design pillars Africa is questionable. Very few failur...

A novel class of amide-functionalized pillar[5]arenes, that is, alkyl and aryl amide derivatives, has been synthesized. Highly selective binding of the dihydrogen phosphate anion over a range of anions by the new synthetic receptors is reported. First, the "binding strength-selectivity" relationship has been decided for the pillar[5]arene/anion systems.

Enhanced shear adhesion of mechanically interlocked dual-scaled micropillars embedded with silica particles is demonstrated. Arrays of elastomeric polyurethane acrylate micropillars with variable pillar diameter, height, aspect ratio (AR1⁄4diameter/height), and spacing ratio (SR1⁄4pillar-to-pillar distance/diameter) are decorated with silica particles of 100nm to 1mm on the pillar heads. The hi...