Mechanisms of abrupt surface subsidence induced by repeated mining beneath residual coal pillars: a case study of Tashan Coal Mine, China

Abstract

Clarifying the formation mechanism of residual pillar instability and abrupt changes in surface subsidence induced by repeated mining beneath residual coal pillars is important for subsidence-hazard prevention and control under this special geological and mining condition. Based on the 8104 working face of Tashan Coal Mine, a two-dimensional numerical model was established to analyze the evolution of overburden stress, displacement, and plastic failure during repeated mining, and to examine how geological and mining parameters affect the development of abrupt subsidence changes. The results show that surface subsidence develops in stages during repeated mining. The maximum surface subsidence is 112 mm when the working face advances to 600 m, but increases sharply during the 600–800 m stage, reaching 2700 mm at 800 m. The development of abrupt subsidence changes is jointly controlled by mining disturbance intensity and the bearing capacity of the residual pillar group. Smaller interburden thickness, lower pillar width-to-height ratio, and larger lower-seam mining thickness make the residual pillar group more prone to reactivation and instability, causing abrupt changes in surface subsidence to occur earlier. The results provide a reference for risk identification of abrupt subsidence changes and mining-parameter optimization under similar conditions.