Backfilling mining technology and rational process design for coal seams beneath urban buildings

Zhang Yang; Zhou Yushun; Wang Fangtian; Lu Yan; Hao Wenhua; Wang Xu

doi:10.16186/j.cnki.1673-9787.2025080034

Abstract：Objectives To address the challenge of large amounts of coal resources constrained beneath ur-ban buildings,which restrict the sustainable development of coal mines,Chengjiao Coal Mine was selected as a test site to investigate rational backfilling mining technologies and process designs for coal seams be-neath urban buildings.Methods Using engineering analogy,scheme comparison,and theoretical calcula-tion methods,and based on the principle that backfilling mining beneath buildings must prevent surface subsidence,four mining schemes were proposed:fully mechanized mining with cemented paste backfill-ing,new solid backfilling mining,super-high-water backfilling mining,and overburden isolation grouting backfill mining.The strata control effects of different schemes were analyzed,and the optimal scheme was determined as fully mechanized mining with cemented paste backfilling.Support height was determined ac-cording to coal seam thickness,and the working resistance of the support was calculated based on resis-tance to lateral paste pressure and control of roof subsidence at the filling face.A coordinated"isolation-backfilling-coal mining"process was designed to eliminate mining-filling interference.Based on the roles of the backfilling body during the solidification and coal mining stages,the early strength,stability safety fac-tor,and later-stage strength of the backfilling body were determined.Mix proportion experiments and me-chanical property tests of paste backfilling materials were conducted.Results The minimum and maximum structural height of the paste backfilling support are 2.0 m and 3.8 m,respectively,with an extension ratio of 1.9.The working resistance of the support exceeds 8 250 kN.The compressive strength of the paste back-filling body is not less than 0.06 MPa during the solidification stage and not less than 0.16 MPa during the coal mining stage.With a strength stability safety factor of 2.5,the uniaxial compressive strength of the paste backfilling body after 28 days of curing is not less than 2.97 MPa.Economical mix proportions that satisfy strength requirements were obtained for fly ash paste and gangue-fly ash paste backfilling materials.Conclusions The rational backfilling mining technology and process design for coal seams beneath urban buildings applied at Chengjiao Coal Mines can provide valuable references for similar mines in China.