Asymmetric evolution of overburden fractures and roof water-hazard zoning during sequential mining of closely spaced coal seams

Sequential mining of closely spaced coal seams creates complex relations among residual fractures, cumulative damage, current loading, and roof water hazards. Panels 11,201, 11,200, and 22,201 at Hujia-ta Coal Mine were investigated in their actual sequence using empirical calculation, physical simulation, abutment-pressure and microseismic monitoring, 3DEC, TEM surveys, and drainage drilling. After adjacent extraction of panels 11,201 and 11,200, visible fracture height increased from 55.3 to 56.2 m (1.6%), whereas the boundary-angle difference increased from 0° to 7°, showing a clearer response of boundary geometry. After repeated extraction of panel 22,201, the maximum fracture-height ratio between the 11,200 and 11,201 zones was K H = 1.65, while the right-to-left abutment-pressure peak ratio was K P = 1.93, indicating spatial non-coincidence between the cumulative visible-damage extreme and current load peak. At a mean burial depth of 254.3 m and an interburden thickness of 44 m, the empirical damage height was 110.2 m. Integrated evidence delineated Class I coupled priority zones and Class III anomaly target zones; no Class II target was identified, only interpretable areas not assigned to Classes I–III were classified as Class IV background zones, and the 1520–1940 m equipment-interference section was left unclassified. Two drainage stages completed 8 drill sites, 27 boreholes, 2450 m of drilling, and 15,024 m 3 of drainage. All 21 Stage−2 boreholes reached the target goafs; maximum inflow and water pressure were 22 m 3 /h and 0.32 MPa. After drainage, the goaf-water-related low-resistivity response was not detected under comparable surveys, and roof-aquifer anomalies decreased from three to one. Mechanical damage, electrical response, and hydraulic connectivity should be treated as distinct but complementary evidence layers for drilling targets and drainage priorities.