Mechanisms of the abnormal first weighting in 'knife handle shaped face' with 7.0 m high supports
During the mining process of the 'knife handle shaped face' (KHSF) No. 52304-1 with 7.0 m high supports in Daliuta coal mine, the first weighting intensity was extraordinarily weak although the mining distance reached 171 m. This was quite different from the current experience. In this research work, field measurements and theoretical analysis were conducted to study the mechanisms of this uncommon phenomenon. The results showed that, the sub key stratum 1 (SKS 1), which commonly played a major role in mining face strata behaviour, had broken before the first weighting. And because of its high horizontal distance above the coal seam, its long breakage interval, as well as the large bulking factor of the immediate roof, its breakage did not have influence on the mining face. Therefore, the reason for the unusual weighting intensity of first weighting was not because of the breakage of SKS 1 but due to the fracturing of the upper primary key strata (PKS). Also, as PKS was far away from the coal seam, its breakage had only little influence on mining face so that the weighting intensity was quite weak.