Pillar stability continues to be a significant concern in multiple-level mining conditions, particularly for deep mines when pillars are not stacked or the thickness of interburden between mining levels is thin. The National Institute for Occupational Safety and Health (NIOSH) is currently conducting research to investigate the stability of pillars in multiple-level limestone mines. In this study, FLAC3D models were created to investigate the effect of interburden thickness, the degree of pillar offset between mining levels, and in situ stress conditions on pillar stability at various depths of cover. The FLAC3D models were validated through in situ monitoring that was conducted at a multiple-level stone mine. The critical interburden thickness required to minimize the interaction between the mining levels on top-level pillar stability was explored, where the top level mine was developed first followed by the bottom level mine.

The model results showed that there is an interaction between numerous factors that control the stability of pillars in multiple-level conditions. A combination of these factors may lead to various degrees of pillar instabilities. The highest degree of local pillar instability occurred when pillar overlap ranges between 10 and 70%. On the contrary, the highest degree of stability occurs when the pillars are stacked, the underlying assumption is that the interburden between mining levels is elastic (never fails). Generally, for depths of cover investigated in this study, the stability of top-level pillars shallower than 100 m (328 ft) or with interburden thicknesses greater than 1.33 times the roof span—16 m (52.4 ft) in this study—does not appear significantly impacted by pillar offset. The results of this study improve understanding of multiple-level interactions and advances the ultimate goal of reducing the risk of pillar instability in underground stone mines.

矿柱稳定性仍然是多级采矿条件下的一个重要问题，特别是对于矿柱未堆叠或采矿层之间的夹层厚度较薄的深矿。美国国家职业安全与健康研究所 (NIOSH) 目前正在进行研究，以调查多级石灰石矿中支柱的稳定性。在这项研究中，创建了 FLAC3D 模型来研究夹层厚度、采矿层之间的矿柱偏移程度以及地应力条件对不同覆盖深度的矿柱稳定性的影响。FLAC3D 模型通过在多层石矿进行的现场监测得到验证。

模型结果表明，在多层次条件下，控制支柱稳定性的众多因素之间存在相互作用。这些因素的组合可能导致不同程度的支柱不稳定性。当支柱重叠范围在 10% 到 70% 之间时，会出现最高程度的局部支柱不稳定性。相反，最高程度的稳定性发生在柱子堆叠时，潜在的假设是采矿层之间的夹层是弹性的（永不失效）。一般来说，对于本研究中调查的覆盖深度，浅于 100 m（328 英尺）或夹层厚度大于 1.33 倍屋顶跨度（本研究中为 16 m（52.4 英尺））的顶层柱的稳定性不似乎受到支柱偏移的显着影响。