Hydraulic fracturing (HF) has emerged as a widely used ground control strategy in Chinese coal mining practice, often employed in combination with ground support techniques. HF campaigns can be broadly categorized into two types based on the size of the targeted region: local campaigns, which are applied to smaller areas such as the roof above a coal pillar, and large-scale campaigns, which encompass a broader area, such as the entire width of a longwall panel. This paper presents two case studies that examine the use of both local and regional HF as a ground support strategy in Chinese coal mines. The field studies demonstrate that HF is effective in reducing or redistributing mining-induced stresses, preconditioning hard rock strata, and, in some cases, decreasing mining-induced microseismicity.
In contrast to civil tunnels, underground coal mine roadways possess a distinctive characteristic: they are unavoidably subjected to mining-induced stresses, particularly in the entries of longwall panels. As the longwall extraction proceeds, abutment stresses form around the periphery of the mined-out area. The presence of high abutment stresses can result in a range of problems concerning the stability of longwall entries and pillars, such as roof fall, rib failure, floor heave, and even coal burst. At greater mining depths, these challenges become more pronounced owing to the high overburden stresses associated with the relatively brittle response of coal measures. Thus, the development of protective measures to counteract the damaging effects of excessive stresses is necessary.
Destress blasting is a long-established stress relief technique utilized in underground coal mining. Its primary objective is to shift stress concentration zones to the interior rock mass and establish a protective barrier surrounding the excavation (Konicek et al., 2011). In China, destress blasting was successfully implemented to control floor heave in deep coal mines (Kexin, 1995; Xia et al., 2007), as well as to mitigate coal burst issues in Poland, the Czech Republic, China, and Germany (Konicek et al., 2011; Dvorsky et al., 2005; Gu et al., 2016; van As et al., 2004; Catalan et al., 2012). The technique is believed to release stored strain energy and reduce modulus values, thereby ensuring that the rock mass does not bear a critical stress level (Sedlak, 1997).
