Classification Study on Instability Dangerous Source in Widespread Mined-out Area of Coalmine

On the basis of analyzing natural geological factors and index W₁,mining technology factors and index W₂ that influencing widespread mined-out area instability dangerous states,the risk of coalmine widespread mined-out area was classified with comprehensive index method,and the comprehensive index W of grade evaluation in its dangerous state was determined.The instability dangerous source in widespread mined-out area was divided into four: Ⅰ-level dangerous source(extraordinarily serious risk:W≥0.8);Ⅱ-level dangerous source(serious risk:0.6≤W<0.8);Ⅲ-level dangerous source(higher risk:0.3≤W<0.6) and Ⅳ-level dangerous source(general risk:W<0.3).According to the example,the instability risk of widespread mined-out area in one mining area of Hebei was classified and the practice showed that the classification criterions are reasonable and feasible.