Numerical simulation of the evolution of mining-induced stress-damage-seepage fields and surface subsidence characteristics under extremely thick water-bearing unconsolidated layers

Xu Liangji; Xu Huafeng; Liu Xiaopeng; Cao Zongyou

doi:10.16186/j.cnki.1673-9787.2025080033

Abstract：Objectives To elucidate the evolution characteristics of mining-induced surrounding-rock damage and surface subsidence under complex geological conditions involving extremely thick water-bearing uncon-solidated layers,and to investigate the effects of unconsolidated-layer thickness,bedrock thickness,and aquifer dewatering on surface subsidence.Methods The Huaibei mining area,characterized by extremely thick water-bearing unconsolidated layers,was selected as the study region.Numerical simulation was con-ducted using FLAC3D software to implement a stress-damage-seepage coupled mathematical model for coal mining beneath unconsolidated layers.The evolution of mining-induced surrounding-rock damage,perme-ability coefficient,and surface subsidence in both mined and unmined areas was analyzed.Results After mining,the surrounding-rock damage zone and high-permeability zone exhibited a saddle-shaped distribu-tion.Increasing unconsolidated-layer thickness led to the expansion and interconnection of primary fractures in the weathered zone,forming preferential seepage pathways that guided groundwater infiltration from the fourth aquifer.This induced aquifer dewatering consolidation and intensified surface subsidence,exhibiting a growth pattern characterized by an initial rapid increase followed by gradual stabilization,with the central area of the subsidence basin becoming relatively flat.Increasing bedrock thickness caused the evolutionary height of the damage and high-permeability zones to first rise and then decline.Thin bedrock resulted in greater surface subsidence and more extensive damage zones,while thick bedrock effectively restrained damage evolution in the weathered zone,reduced or prevented infiltration from the fourth aquifer,and miti-gated compressive subsidence caused by aquifer dewatering.Conclusions Both unconsolidated-layer thick-ness and bedrock thickness significantly influence the distribution of mining-induced surrounding-rock dam-age and permeability evolution.The extremely thick unconsolidated layer acts as an overburden load on the bedrock,while bedrock thickness regulates the extent of damage evolution by controlling the bearing capac-ity of key strata.The weathered zone in direct contact with the fourth aquifer is a critical factor contributing to aquifer dewatering.These findings provide a theoretical basis for water inrush prevention and surface sub-sidence control in coal mining beneath extremely thick water-bearing unconsolidated layers.