Research on Overburden Movement and Surface Subsidence Control of Partial Backfill Mining in Deep Coal Seams Based on NPR-DDA

Targeting the problem of surface subsidence caused by deep coal seam mining, using the 1210 panel of the Shilawusu Coal Mine as the background and based on field-measured surface subsidence data, a numerical model of mining-induced overburden behavior under partial backfill mining in deep coal seams was constructed using the NPR-DDA bonded particle model. The evolutionary laws of overburden fracture and movement during the working face advancement were systematically studied; the dynamic characteristics of the vertical displacement and stress fields were revealed; and the effects of the backfill rate, backfill working face width, caving working face width, and section coal pillar width on surface subsidence were investigated through one-factor-at-a-time analyses to identify the response trends under the specified simulation conditions. The results show that: the measured surface subsidence exhibits an asymmetric, funnel-shaped progressive evolution, with the maximum subsidence (187 mm) located at monitoring point H52 and shifted toward the left side of the goaf; when advanced to 100 m, the immediate roof collapses first (maximum subsidence of 4.4 m), and when advanced to 300 m, sub-key stratum 1 collapses entirely while the bed-separation space beneath sub-key stratum 2 shrinks, resulting in compression and consolidation of the broken rock mass in the goaf; and partial backfilling plays an active supporting role, with the average vertical stress in the central backfilling zone reaching 19.38 MPa; under the conditions of the respective simulation groups, increasing the backfill rate, backfill working face width, and section coal pillar width reduces the magnitude of maximum surface subsidence from 1501 to 652 mm, from 1632 to 930 mm, and from 1264 to 513 mm, respectively, whereas increasing the caving working face width increases it from 1023 to 2357 mm. The findings provide a reference for evaluating partial backfill mining schemes for the unmined 1210 panel at the Shilawusu Coal Mine.