Characteristics of rock strength failure and identification of hazardous areas in the roof of deep mining stope

Abstract

The roof of deep mining stopes is notoriously unstable and challenging to manage due to high in-situ stress and deteriorating rock conditions. To address this issue, a comprehensive approach was employed, incorporating indoor physical experiments, numerical simulations, and field tests to investigate the stope roof rock composition characteristics and strength failure modes in the Laoyingshan deep coal mine. The study revealed the distribution characteristics of the high in-situ stress field in this mining area and delineated different levels of hazards in the roof. The results indicate that, under identical lithological conditions, the mineral composition of deep rock formations is complex. Changes in some mineral components and properties were observed, leading to increased expansiveness and water absorption in clay minerals such as sodium montmorillonite and kaolinite within the basic roof layer. In simulated tests of surrounding rock strength in deep mining stopes, as stress levels approached 2 MPa, the damage factor increased, showing a trend of localized concentration. Internal damage began to exhibit noticeable spatial evolutionary expansion patterns and gradual nucleation. When stress exceeded 8 MPa, rocks transitioned from macroscopic fracture surfaces to microscopic fragmentation zones, with a sudden decrease in stiffness degradation values, internal instantaneous collapse, and phenomena akin to “rock burst” under high stress disturbance. In-situ stress testing determined that the stress field in the deep mining zone of Laoyingshan is in a thrust fault stress state, with horizontal stress predominance. The maximum stress direction is predominantly southwest-northeast, with stress magnitude reaching 25.49 MPa. By arranging post-mining and pre-mining borehole observation stations and utilizing image grayscale fracture recognition technology in MATLAB, the roof was classified into four danger levels: “extremely broken,” “broken,” “significant fractures,” and “minor fractures.” Main control measures for coupling grouting in deep-shallow zonation rigidity were proposed based on these classifications.