Evolution Characteristics and Instability Analysis of Stratified Roof Structure in Roadway with Different Stress Levels

With the extension of mines to deep mining, horizontal stress has become an important factor in the stability of the roadway surrounding rock, and the influence of horizontal stress on the structure of a layered roof is more complex. The simulation test of a layered roof of a roadway under different lateral pressure coefficients was carried out by using a self-designed test device and discrete element simulation software. The crack coalescence behavior of a layered roof in a roadway was analyzed, and the critical stress of rock beam failure in each layer was determined. The results show that the larger the stress levels, the larger the number and height of cracks in the layered roof were, and the relationship between them can be characterized by a quadratic polynomial. With the increase of stress levels, the layered roof was damaged gradually from the bottom to the top along the bedding plane. The maximum height of the roof caving was 9, 23, 31, and 39 mm, respectively. The width of the upper roof caving was 72, 35, 31, and 27 mm in turn. The left angle of the caving range had little change (about 60°). With the increase of stress level, the maximum caving height of the layered roof tended to increase, while the width of the top surface tended to decrease. The relationship between the stress level and the height and width can be represented by a quadratic polynomial and exponential function. According to the stability theory of the compression bar, the critical stress of failure and the decrease of the span of the rock beam in each layer were determined respectively, and the reasons for the instability of the layered roof caving are explained.