Research on the Mechanism of Multiple Key Strata Controlling Overburden Movement and Their Classification in Bedrock Gully

In most cases, there is more than one key strata in the overburden of bedrock valley mining areas, and the integrity of these layers is compromised by terrain cutting. Dynamic formation pressure and extensive surface cracks often occur during coal mining, posing significant risks to the safety of mines. Therefore, Double key stratum conditions of the overburden in the BJG coal mine are taken as the background, physical similarity model experiments are established to analyse the deformation and fracture laws, bearing capacity, and overburden migration characteristics of different occurrence states of key stratums in the bedrock valley mining area. Furthermore, the mechanism of controlling overburden movement by multiple key strata, and a method for identifying and classifying multiple key strata, are studied in the bedrock valley terrain. The results indicate that: (1) When the key stratum sequence is missing, during the mountain mining stage, the key stratum breaks frequently and the break distance is small, and the overburden undergoes intense block rotation movement; During the extraction stage, the number of key stratum fractures decreases and the fracture distance increases, and the intensity of overburden movement weakens, resulting in layered fractures; (2) In gully terrain, the occurrence state of the key strata determines their bearing capacity and the intensity of slope movement due to mining; (3) In gully terrain, key strata with missing sequences cannot effectively transmit horizontal stress and are considered weak key strata, whereas those without missing sequences are strong key strata. This study provides reference and guarantees for mine design, safe and efficient mining under similar conditions.