Abstract:
To identify goafs left over from historical mining before the integration of Nanling Coal Mine, the microtremor exploration technique was adopted. A linear rolling observation array was laid out for coal mining subsidence zones formed in the north-central part of the mine field prior to integration, considering the complex topographic conditions of the working area. Microtremor data inversion calculations were carried out based on an adaptive genetic algorithm, and two survey lines WD1 and WD2 were arranged. Low-velocity anomaly zones (shear wave velocity < 1 250 m/s) were delineated at the “zigzag” or “V-shaped” inflection points where the apparent shear wave velocity of strata decreased significantly, so as to determine the boundaries of goafs. To verify the accuracy of the test results, the test results were compared with the historical mining data collected by the mine. The low-velocity anomaly areas delineated by the test were basically consistent with the historical mining areas. Drilling verification was carried out in the auxiliary air intake roadway of the No.2 mining district of No.5 coal seam. Among them, borehole No.3 was drilled to 66.3 m, borehole No.4 to 77.6 m, and borehole No.7 to 104.7 m, respectively revealing No.2 coal goaf. The boundary errors between the detected goaf and the experimentally determined goaf were all about 20 m. In the subsequent practical application, Nanling Coal Mine detected 7 goaf areas of No.2 coal seam on the surface of the No.2 mining district in the northern part of the minefield. Among them, three goaf areas in the same coal seam were revealed by drilling during the earlier roadway excavation of 2101 and 2102 working faces; two overlying No.2 coal goaf areas were revealed by drilling during the recent excavation of the air return roadway of 5211 working face, with a total of 123 000 m
3 of goaf water drained. At present, five goaf areas of No.2 coal seam have been verified underground, with the boundary error of drilling-verified goaf ranging from 25 to 30 m. The remaining two unverified low-velocity anomaly areas are still located in front of the to-be-excavated sections of the two roadways of 5211 working face. When the excavation approaches the “three lines” defined with the low-velocity anomaly areas as the center, the mine must strictly follow the goaf water detection and drainage design to eliminate the potential safety hazards caused by hidden disaster-causing factors.