A proposed method for optimizing coal pillar design using coalffeld-speciffc uniaxial compressive strength

摘要

TTe research described considers whether the variability in coal material strength, as derived through a series of uniaxial compressive strength (UCS) tests, could be used to indicate the variability in coal pillar strength. TTe aim is to be able to use a distribution of UCS tests as input into the coal pillar strength calculation. TTis will allow the pillar design to be expressed in terms of a probability of failure rather than as the commonly used safety factor. To achieve this, the bulk strength factor associated with commonly used pillar strength formulae was replaced with a distribution of UCS results divided by an adjustment factor. TTe factor was determined so as to ensure that the resulting bulk strength does not deviate from the statistically determined bulk strength published in the original formulae. TTis approach enabled pillar strength distributions to be obtained using industry-accepted strength formulae, subsequently allowing for a probability of failure to be calculated for a speciffc pillar design. Using a regional coal material strength curve as a baseline, coalffelds in which the coal is stronger than the regional mean can be identiffed and the pillar designs optimized. TTis is based on the stronger coals achieving lower probabilities of failure at similar safety factors. TTe research has considered actual UCS data from multiple mines in the Mpumalanga coalffelds of South Africa, and has proved that the variability in material strength between coalffelds could allow for some optimization using the proposed approach. Based on the data used in the study, a 2.78% increase in extraction could be achieved. However, further research will be required to validate the results of the study in an underground environment.