Hazard assessment of strong mine pressure at working face crossing coal pillars in shallow closely spaced coal seams

When lower seams in shallow closely spaced coal seam groups are mined beneath overlying residual coal pillars, strong mine pressure hazards characterized by step subsidence of the roof or support crushing can readily occur, and their quantitative hazard assessment is difficult for field control. With Shendong mining area as the engineering background, a method was proposed for assessing strong mine pressure hazard at working faces crossing coal pillars in shallow closely spaced coal seams. Based on a mechanical model of the coupled roof structure comprising inverted-trapezoidal overburden and interburden during coal pillar crossing, nine key indicators, including inter-mining ratio, angle between coal pillar and working face, and interburden stability, were identified; a three-level hierarchical evaluation system encompassing geological conditions, coal pillar attributes, and engineering parameters was constructed; and four-level quantitative classification criteria (weak, general, medium, and high hazard) were established for the indicators. The Analytic Hierarchy Process was used to calculate the weights of the evaluation indicators, and the top three indicators by composite weight were inter-mining ratio, angle between coal pillar and working face, and interburden stability, in descending order. The weighted summation method and fuzzy comprehensive evaluation method were used separately to assess strong mine pressure hazard during coal pillar crossing, and the applicability of the two methods was analyzed. The results showed that the maximum membership principle of fuzzy comprehensive evaluation would weaken potential risk information from non-dominant grades. Therefore, the weighted summation method was recommended as the primary evaluation model and fuzzy comprehensive evaluation as an auxiliary validation model. The rationality of the proposed method was verified using field-measured data from six typical working faces crossing parallel coal pillars in Shendong mining area.