Failure height and characteristics of overlying strata in high-intensity mining with thick soil and thin bedrock

To investigate the failure characteristics of overlying strata during high-intensity mining of thick soil layers and thin bedrock,this study examines the 12305 working face of Qianshuta Coal Mine. The movement and failure of overlying strata under geological conditions characterized by thick soil layers and thin bedrock after mining were analyzed using UDEC numerical simulation,field measurements,and theoretical analysis. The results showed that overburden failure height presented three stages:slowly increasing,suddenly increasing,and stable. The slowly increasing and suddenly increasing stages mainly occurred in thin bedrock,while the stable stage occurred in thick soil layers. Additionally,the thick soil layer exhibited a certain liquid index,leading to the lag of surface subsidence. By observing the leakage of flushing fluid and water injection tests,the height of the water flowing fractured zone inthis working face was found to be 84.5-86.5 m,and the fracture-mining ratio was 7.9-8.1. The numerical simulation and theoretical calculation results were consistent with the measured results. The "two-zone" failure mode of thick soil layers and thin bedrock was also expounded,with thin bedrock acting as support and thick soil layers as load. The study provides useful reference for enhancing the safety of mining operations under similar geological conditions.