Longwall mining is a highly productive and efficient coal mining method used in the USA. During longwall retreating, the belt entry must be maintained stable, and any roof fall in the belt entry would jeopardize mine safety and substantially interrupt the continuous production of coal in the longwall face. Past experience of longwall mining has shown that belt entry stability was the greatest challenge in longwall ground control, and the occurrence of roof falls in belt entries was largely associated with high horizontal stress. To properly support the roof in the belt entry, it is important to understand how longwall-induced horizontal stress changes affect roof stability in belt entries and to strategically install supplementary support to prevent any potential roof falls. Researchers from the National Institute for Occupational Safety and Health (NIOSH) performed horizontal stress measurements in the immediate roof of the belt entries for two Pittsburgh seam longwall panels oriented unfavorably to high horizontal stress. Hollow inclusion cells (HICells) were installed in the immediate roof at the intersection in each of the belt entries, and stress changes were monitored as the longwall face was approaching and passing the intersection. Numerical models were set up to calculate the longwall-induced horizontal stress changes in the roof at the monitoring sites. With the verified model, investigations were made of how horizontal stress is concentrated and relieved in the belt entry roof near the face under different panel orientations. Both measurements and modeling results showed that high horizontal stress is concentrated in the roof in the belt entry within about 15 m outby the face when a longwall panel is unfavorably oriented to the major horizontal stress. The study demonstrated that longwall-induced differential horizontal stress can be used as an indication of the degree of horizontal stress concentration. Roof support strategies are discussed on how to maintain the stability of belt entry under high horizontal stress concentration.

长壁开采是一种在美国使用的高产高效的煤炭开采方法。长壁后退过程中，带入口必须保持稳定，带入口中的任何顶板掉落都会危及煤矿安全，并严重中断长壁工作面煤炭的连续生产。以往的长壁开采经验表明，带入口稳定性是长壁地面控制的最大挑战，带入口发生顶板塌陷在很大程度上与高水平应力有关。为了正确支撑皮带入口处的屋顶，重要的是要了解长壁引起的水平应力变化如何影响皮带入口处的屋顶稳定性，并战略性地安装补充支撑以防止任何潜在的屋顶掉落。美国国家职业安全与健康研究所 (NIOSH) 的研究人员在输送带入口的直接顶部对两个匹兹堡接缝长壁板进行了水平应力测量，这些长壁板的方向不利于高水平应力。空心夹杂物单元 (HICells) 安装在每个输送带入口处交叉口的直接屋顶上，并在长壁工作面接近和通过交叉口时监测应力变化。建立了数值模型来计算监测点屋顶的长壁引起的水平应力变化。通过验证模型，研究了在不同面板方向下，靠近工作面的带入口顶板的水平应力是如何集中和释放的。测量和建模结果都表明，当长壁板不利地定向于主要水平应力时，高水平应力集中在工作面外约 15 m 的带入口处的顶板中。该研究表明，长壁引起的不同水平应力可以用作水平应力集中程度的指示。讨论了屋顶支撑策略如何在高水平应力集中情况下保持输送带入口的稳定性。