Ground Destressing

Two of the key elements associated with outbursts are mine gases and tectonics. Just as gas drainage involves the prevention of outbursts in the seam and or associated rock strata to prevent outbursts. Currently, there are four different mechanisms used to de-stress a seam outburst prevention, these being stress relief drilling, stress relief mining, and inducer shotfiring and water infusion.

Stress relief techniques serve to reduce outburst potential, by reducing the ability of the immediate face to store the energy necessary for outbursts. The fracturing of the immediate face insures that high gas pressures or structural stress conditions do not exist in the next cut. Structural stress is shifted to the solid coal inbye the face. Gas pressure is reduced by coalbed gas flow through the induced fracture systems. Stress relief boreholes of about 100 to 200 mm in diameter are drilled into the face to mechanically destress the coalbed by removing large volume of drill cuttings. Stress relief slot cutting on longwall faces is reported to be highly successful for reducing outbursts. Relaxation slots are systematically cut from 2.0 m to 1.0 m deep into the face, destressing the immediate face area.