Structural evolution of a quasi-granular arch within a thick loose layer and overburden movement behavior

Tan Yi; Wang Yu; Li Hui; Zhang Shaopu; Feng Yixiang; Ge Zhibo; Tang Ze; Zhang Zhixiang

doi:10.16186/j.cnki.1673-9787.2024110017

Abstract：Objectives To investigate the relationship between the development of a quasi-granular arch structure within a loose layer and surface damage,this study examines the structural evolution of the quasi-granular arch and the overburden movement behavior under a thick loose layer.Methods Taking the 2303 working face of Hemei No.5 Mine as the engineering background,PFC particle flow numerical simulation,on-site drilling leakage observation combined with microseismic exploration,and nonlinear regression analy-sis were comprehensively employed.Results The results indicate that,with the advance of the working face,the overall failure mode of the bedrock exhibits a positive trapezoidal shape.Particles at the bottom of the loose layer are disturbed by bedrock bending and subsidence,forming an arch-shaped bonded failure zone.During particle movement and compaction,a quasi-granular arch structure with a certain bearing ca-pacity is gradually formed.The fissure field,stress field,and displacement field show distinct stage-dependent evolution characteristics.The development height of the water-conducting fracture zone experi-ences four stages:rapid growth,slow growth,abrupt increase,and stabilization.The stress field evolution undergoes three stages:development of the bedrock pressure arch,coupled evolution of the pressure arch and quasi-granular arch,and independent development of the quasi-granular arch.Surface subsidence evolves through four stages:slow subsidence,accelerated subsidence,rapid subsidence,and stabilization,corresponding well to the staged evolution of the three fields.Surface subsidence measurements based on a surface monitoring circle show that the subsidence curve is approximately V-shaped.After mining,step-like cracks appear in the central area of the goaf,while tensile cracks develop on both sides,consistent with field investigation results.Field observations indicate that the height of the water-conducting fracture zone reaches 147.46 m,with a fracture-to-mining ratio of 16.49,while the caving zone height is 57.46 m,with a caving-to-mining ratio of 6.43.Based on regression theory,a multivariate nonlinear prediction model for maximum surface subsidence under thick loose layers is established,effectively reducing prediction errors caused by single-factor consideration and achieving a fitting coefficient of 0.98.Conclusions The proposed results and methods provide a useful reference for coal mine safety production and surface protection under similar geological conditions.