Study on Overlying Rock Movement in Mining of Thin Bedrock Face with Thick Unconsolidated Strata

Abstract

China as a big country of coal production and consumption, coal strategic position is key. The condition of thick loose layer and thin bedrock is often encountered in mining. This special geological structure causes the mechanical behavior of coal seam after mining and the deformation and failure law of overlying rock to be different from the conventional condition. Taking the 21106 working face of Xinqiao Coal Mine as the research object, this paper conducts an in-depth study on the overburden fracture law of the working face with thick unconsolidated layer and thin bedrock, and obtains the following results:(1) The mining engineering geological conditions of 21106 face were analyzed, the mining conditions of the face were mastered, the changes in bedrock thickness were revealed, the heights of caving zone and water-conducting fracture zone of the face were calculated, and the bedrock thickness of the face was classified as follows: The area with a bedrock thickness less than 51.7m is divided into thin bedrock area, the area with a bedrock thickness greater than 51.7m and less than 54.7m is divided into a transition area of bedrock thickening, and the area with a bedrock thickness greater than 54.7m is divided into a thick bedrock area, and the thin bedrock research area of the working face is determined.(2) The numerical model of the working face is established and the overlying rock breaking characteristics are mastered. The overlying rock breaking of the working face can be divided into four stages: basic roof breaking stage Ⅰ, pseudoplastic rock beam forming stage Ⅱ, loose layer caving arch forming stage Ⅲ and loose layer caving arch transverse development stage Ⅳ. The characteristics of stress arch evolution in the working face are understood: the stress arch structure gradually expands from the direct top to the loose layer, and the compaction area of caving rock continuously increases, which causes the fractal migration of stress arch and forms an asymmetric double arch structure on both sides of the goaf.