The transmission mechanism of bedrock-surface subsidence in ultra thick coal seam mining under the influence of aeolian sand thickness

ZHANG Cun; REN Zhaopeng; WANG Yongpeng; LIAN Yongqi; LI Quansheng; LI Xiaobin

doi:10.13247/j.cnki.jcumt.20250234

Abstract：Surface subsidence in aeolian sand-covered coal mines represents a coupled failure mechanism involving bedrock subsidence and fluid-like response of overlying granular strata,where aeolian sand properties significantly influence surface deformation.To reveal the impact mechanism of aeolian sand thickness on bedrock-to-surface subsidence propagation under high-intensity mining in Shendong Coalfield,this study integrated field measurements,theoretical analysis,and numerical simulations to investigate subsidence propagation characteristics.A dual-medium subsidence propagation model was established based on physical-mechanical prop-erty contrasts and stress interactions between bedrock and aeolian sand,with a surface predic-tion formula derived from elastic foundation beam theory that accounts for both media under full extraction conditions.A novel block-particle coupled discrete element method was devel-oped to simulate dynamic bedrock-surface coupling deformation through cyclic stress transfer between bedrock damage patterns and basal stress redistribution in aeolian sand,thereby re-vealing subsidence propagation features and quantifying surface deformation under varying sand thicknesses.Field measurements show the relative surface settlement at the top of the bedrock is only 75-126 mm,indicating primary key stratum controlled synergistic subsidence propagation.As aeolian sand thickness increased from 9 m to 23 m,the surface subsidence fac-tor decreased by 6.45％-26.58％.Simulations further demonstrate that when sand thickness rose from 8 m to 40 m,the bedrock-to-surface subsidence attenuation escalated from 6.41％to 12.82％,confirming thicker sand layers retard subsidence propagation.In addition,the poros-ity of aeolian sand increased by an average of 0.085 3 before and after mining with different ae-olian sand thickness models,causing the subsidence space of the bedrock to dissipate in the voids of aeolian sand during the upward conduction process.Cross-validation among field data,simulations,and theoretical predictions verifies the reliability of both the numerical method and dual-medium prediction model.This research elucidates the dominant control behavior of bedrock under thin aeolian sand cover and the energy-dissipation buffering effect of thick sand layers,providing a scientific basis for surface deformation prediction and control in analogous mining areas.