Mining Publication: A New Method to Calculate Permeability of Gob for Air Leakage Calculations and for Improvements in Methane Control

The porosity and permeability of the caved zone in a longwall operation impact many ventilation and methane control related issues, such as air leakage into the gob, the onset of spontaneous combustion, methane and air flow patterns in the gob, and the interaction of gob gas ventholes with the mining environment. Despite their importance, the gob is typically inaccessible for performing direct measurements of porosity and permeability. Thus, there has always been debate on the likely values of porosity and permeability of the caved zone and how these values can be predicted. This study demonstrates a fractal approach that allows the calculation of porosity and permeability from the size distribution of broken rock material in the gob, which can be determined from image analyses. The fractal approach presented here constructs flow equations and fractal crushing equations for granular materials to predict porosity for a completely fragmented porous medium. The virtual fragmented fractal porous medium so generated is exposed to various uniaxial stresses to simulate gob compaction and porosity and permeability changes during this process.