Identification of mine roof susceptibility to air slacking

Air slacking is an intuitive term used by many underground coal miners to describe the deterioration of mine roof, usually shale, due to a change in atmospheric conditions. Several major research studies support humidity changes as being the major cause for the phenomenon. Research has also suggested a relationship between air slacking and cyclic dilation-contraction response to atmospheric humidity changes. There is evidence that, in susceptible rocks, the strains developed may be sufficient to introduce extensive fracturing, observable as mine roof deterioration. It is suggested that comparisons of specialized swelling strain measurements, made under varying humidities, to rock strength and stiffness data could provide an index correlatable to susceptibility to deterioration.