Difference in Surface Damage between Deep and Shallow Mining of Underground Coal Resources in China

The mining of underground coal resources often results in extensive damage to the ground surface, particularly in China, which has a large amount of coal resources. However, the laws of surface damage caused by the mining of deep and shallow underground coal resources are relatively different. This study analyzes the difference in surface damage induced by deep and shallow mining and its mechanism by field measurement and similar material simulation experiments. Surface damage is mainly manifested in the form of cracks, which can be categorized as permanent and dynamic cracks. Permanent cracks occur above the mining boundary of shallow and deep coal mines. Dynamic cracks (including dynamic stretching cracks and stepped cracks) only appear above the goaf in shallow mining. This disparity is due to the fact that strata movement in deep mining occurs in a “three zones” mode, with the failure height of strata increasing with the mining degree in an “S” shape. However, rock strata movement in shallow mining follows a “two zones” mode, with the failure height of rock strata increasing exponentially with the mining degree. Thus, the rock strata are prone to slide and become unstable in the form of benched rock beams, producing dynamic cracks, such as stepped cracks on the surface. This research improves the existing mining subsidence theory and provides technical support for relevant mines to take targeted treatment measures.