Abstract
The hard roof of coal mines has the characteristics of high hardness, good integrity, and large layer thickness, which leads to many ground control problems. To reveal the influence of a hard roof structure on the stress performance and coal pillar stability during mining operations, the 8,104 and 8,105 working faces in the Tongxin coal mine were considered as the research object to analyze the stress behavior during the working face advance. Numerical simulation software FLAC3D was used to establish the numerical model of the longwall face under hard roof conditions. The stress distribution laws and coal pillar stability under different roof strengths were analyzed so as to explain the impacts of the hard roof on the stress distribution at the working face. The results show that during the second face proceeding, the influence zone of the front abutment pressure under hard roof conditions is 6 m wider than that under soft roof conditions, and the bearing stress at the working face is 10.4 MPa higher. At the mining position, the plastic zone of the pillar under hard roof conditions is 11 m wider than that under soft roof conditions, and the peak vertical stress is 5.13 MPa higher than that under soft roof conditions. At 25 m ahead of the working face, the plastic zone of the pillar under hard roof conditions is 6 m wider than that under soft roof conditions, and the peak vertical stress is 24.84 MPa higher than that under soft roof conditions. Additional overburden pressure produced by the uncaved hard roof increased pillar stress and plastic zones. Therefore, the hard roof is the main cause of strong ground pressure behavior in the Tongxin coal mine. Aiming at the strong mine pressure behavior, it is suggested to adopt the pre-splitting technology to reduce the influence of the hard roof on mine pressure.
Highlights
In coal mining, hard and difficult-to-collapse roofs refer to thick, stable, and hard rock layers such as sandstone, conglomerate, or limestone that occur above the coal seam or directly on the thin layer and have the characteristics of high strength, undeveloped joints and fissures, and large thickness
The mining stress distribution at the working face is analyzed based on numerical simulation and comparison with the mining process with soft roofs
It is found that the difference in the mining stress distribution is bigger in the second face mining
Summary
Hard and difficult-to-collapse roofs refer to thick, stable, and hard rock layers such as sandstone, conglomerate, or limestone that occur above the coal seam or directly on the thin layer and have the characteristics of high strength, undeveloped joints and fissures, and large thickness. The hard roof structure is frequently encountered in many mining areas. In China, the quantity of coal seams with hard overlying strata accounts for about one third of the total reserves and are distributed in over than 50% of the mining districts (Yang et al, 2019). Mining-Induced Stress Under Hard Roofs typical area characterized by hard roof strata in China (Liu et al, 2021). During mining of the coal seam with hard roofs, it is difficult to effectively predict and overcome the accompanied problems such as roadway serious deformation, abnormal mine pressure, and engineering disasters. It is necessary to intensively study the instability mechanism when mining the coal seam with hard roofs and deeply understand the rules of ground pressure performance in hard-roof coal mining
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