Strength of the coal seam
The strength and elastic module of the coal seam influence
the fracture mechanics of an outburst. Stored elastic strain energy is
released, and
the failure is usually brittle indicating that the strain energy is not
being used to distort the strata and a large proportion is still stored
at the moment of breakage. Therefore, the ability of the seam to accumulate
elastic strain energy is a large factor in assessing the liability of
an outburst in the seam. (Lama & Bodziony, 1996)
A commonly used index for the ‘bursting liability’ of a
coal seam is the strain energy index,known as "Wet". Wet is
the ratio of accumulated elastic strain energy to the permanent strain
energy. The Wet values for a particular seam may be found either through
laboratory experiments or by in-situ evaluations, with a Wet value greater
than 5 indicating a seam is severely prone to outburst. The strain energy
for an entire seam can be found by taking the mean of the values obtained
for samples in key areas of the strata. |