Main factors influencing the wide range of apertures (from 50 to 400 mm) of mining-induced horizontal fractures (Torezko-Snezhnyanskaya coal area, Ukraine) at traditional (without grout injection into bed separation) longwall coal mining were analysed. Apertures of these fractures were directly measured (using an original experimental device) in vertical boreholes drilled from ground surface to active underground coal workings. It is revealed that main factors influencing the apertures of mining-induced horizontal fractures are thickness of extracted coal seam, distance from extracted coal seam to horizontal fracture, uniaxial compressive strengths of rock layers above and below the fracture, thicknesses of rock layers above and below the fracture, and thickness of “layer-bridge” (key strata). It is argued that influence of above-mentioned factors on the aperture is strongly dependent on combinations (Cases 1–5) of values of these factors. The mathematical forms of correlations (and values of involved empirical coefficients) and role (dominant or insignificant) of each factor in each of five Cases are discussed.

中文翻译：

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影响长壁煤层开采水平裂缝口径的主要因素分析

分析了传统的长壁采煤法（未向层分离注浆）中，由采矿引起的水平裂缝（乌克兰的Torezko-Snezhnyanskaya采煤区）的大孔径（50-400mm）的主要影响因素。这些裂缝的孔径直接（使用原始实验设备）在从地表到活跃的地下煤层的垂直钻孔中进行测量。结果表明，影响水平井缝的主要因素有：煤层厚度，煤层至水平裂缝的距离，裂缝上下岩石层的单轴抗压强度，上下岩石层厚度。裂缝和“层桥”（关键层）的厚度。有人认为，上述因素对孔径的影响在很大程度上取决于这些因素的价值组合（案例1-5）。讨论了五个案例中每个案例的相关性（以及相关经验系数的值）和每个因素的作用（主要或无关紧要）的数学形式。