Synergistic optimization of stope structural parameters and backfill strength in deep large-scale backfilled stopes

Abstract To address post-peak rock damage, mining-induced disturbance superposition, and backfill-strength matching in deep large-scale stopes, this study investigated the − 400 to − 450 m test stopes of the Tianxing iron mine. A three-dimensional FLAC3D model incorporating cohesion weakening and friction strengthening was established to evaluate stope span, mining sequence, panel pillar width, and staged backfill strength. Supplementary analyses considered stope height, lateral pressure coefficient, multi-factor combinations, and rock mass–backfill contact conditions. The CWFS parameters were calibrated using monitored roof settlement and panel pillar stresses, whereas drift convergence was retained for independent validation. The results showed that the 18 m × 50 m scheme increased ore tonnage by 20.00% relative to the 15 m scheme without forming a through-going plastic zone. Interval mining with timely backfilling reduced disturbance superposition, while increasing the first-step backfill strength from 2.0 to 3.0 MPa reduced the maximum displacement by only 0.08 cm. The orthogonal analysis indicated that mining sequence, stope span, and pillar width primarily controlled roof settlement, plastic damage, and pillar stress, respectively. The comprehensive risk indices of the 15, 18, and 20 m schemes were 0.300, 0.573, and 0.700. Therefore, the 18 m span, 15 m pillar, timely backfilling sequence, and staged strengths of 2.0 and 0.5 MPa were selected as an engineering compromise between stability and production scale. Highlights 1.A wider 18 m layout increased ore production by one-fi fth while maintaining ground stability.2.Alternating excavation and prompt fi lling reduced the build-up of ground disturbance.3.Strengthening the initial fi ll beyond 2.0 MPa gave little added benefi t, saving materials.