Pillars in mines are conservatively designed by means of empirical approaches or numerical methods. However, some pillars may become unstable during mining operations. To investigate the possibility of cabling pillars as a means of controlling their stability, a number of typical rock specimens (as for compressive strength tests) were cabled and then subjects to standard compressive strength tests. These tests were extended well beyond the typical strain ranges so as to achieve axial strains of over 5%, estimate the residual strength and measure axial and radial strain up to the end of the test. Complete stress-strain curves for the reinforced specimens tended to behave less stiffly in the post-peak state; furthermore, residual strength increased and dilation and the ability of the specimens to withstand residual loading after great straining decreased. The results were extended to understanding the behaviour of mine-scale cabled pillars.
Although room-and-pillar underground mining is a poor method in terms of mineral recovery, it is still widely used for economic and environmental reasons. Pillar stability plays a key role in the feasibility of these mines, so pillars are conservatively designed using empirical approaches or numerical methods. Pillar instability is often the result of natural variability in rock strength, discontinuity occurrences and local geometry changes. This kind of problem has to be resolved rapidly to prevent overloading the remaining pillars, as this could lead to extended or progressive instability and failure. Once pillars have attained their peak strength, steel cables can be used to enhance stability by controlling lateral strain and yield (Figure 1).
The authors successfully applied this concept to a small iron room-and-pillar mine (Arzúa et al. 2014a). The main aim of our research was to enhance understanding of the method by demonstrating its sound scientific grounding. A number of typical rock specimens (as for unconfined compressive strength (UCS) tests) were cabled and subjected to standard compressive strength tests. Particular attention was paid to extending the tests well beyond typical strain limits in order to achieve axial strains of well over 5%, estimate the residual strength of the cabled specimens and measure axial and radial strain up to the end of the test. This paper describes and interprets laboratory test results and extends them to mine-scale pillar behaviour.