Insights into porosity evolution and compressive deformation of coal gangue-loess composite backfill material after lateral cyclic loading

Coal gangue backfill material undergoes continuous compressive deformation under overburden stress, leading to strata failure and surface subsidence. To address these issues, loess addition combined with lateral cyclic loading was proposed to enhance the compressive deformation resistance of coal gangue-loess composite backfill material (CGLCBM). Biaxial loading tests were conducted to investigate the effects of loess-gangue mass ratio (LGMR), lateral stress, and loading cycles on CGLCBM’s compressive deformation, lateral strain, and porosity. Macroscopic and microscopic analyses revealed the influence mechanisms of LGMR and lateral cyclic loading on CGLCBM’s mechanical behavior. The optimal LGMR was determined as 1:10. Field application at Xingdong Coal Mine’s 11235 working face employed 1.2 MPa lateral stress and four loading cycles, resulting in 0.75 m roof subsidence and 0.16 CGLCBM strain. These findings provide theoretical basis for material proportioning and lateral loading parameter design, promoting efficient solid waste utilization in mining engineering.