Study on the impact of microscopic characteristics of loess at different depths on mining subsidence

In order to investigate the impact of loess micro characteristics on surface movement and deformation during the mining of thick loess layers, a case study was conducted in a mine in Shanxi Province. A combined approach of physical experiment and numerical simulation was used to analyze the particle composition and microstructural characteristics of loess at different depth conditions. A layered model of thick loess layers was established to study the deformation characteristics of the surface under different loess layer thickness conditions. The research revealed the influence of variations in loess microstructure on surface movement and deformation. Research has shown that: with the increase of loess depth, the content of silt particles decreases continuously, while the content of clay and colloidal particles increases. The microstructure changes from a columnar-like arrangement to a spherical-like embedding, ultimately forming a cemented agglomerate structure. The pore space transitions from interconnected compressible pores to embedded pores, eventually forming micropore spaces; the mining of the 150-meter thick loess layer in the mine resulted in a maximum surface subsidence of 4.112 m and a maximum horizontal displacement of 1.327 m. The movement and deformation of the 20 m loess layer were lower than those of the surface loess. The compression of the loess accounted for approximately 12.4% of the maximum surface subsidence, mainly occurring in shallow layers of the surface; as the soil-rock ratio increases, the surface subsidence and horizontal displacement exhibit a first-increase-then-decrease trend. The turning points occur at soil-rock ratios of 1.33 and 1.67, respectively. The variation of loess microstructure with depth has a buffering effect on the macroscopic subsidence of the surface.