Practices, experience, and lessons learned based on field observations of support failures in some Chinese coal mines.

Modelling, experimental study, and field observation are prevailing research methods in coal mine support application. Many criteria and rationales have been established to evaluate the stability of coal mine excavations from both qualitative and quantitative perspectives. Nevertheless, most coal mine support designs are still highly dependent on empiricism or semi-empiricism, even with the existence of the aforementioned theories. Oftentimes, most lessons are learned via the trial and error approach. A more critical fact is that further in-depth improvement of or research into coal mine support appears to be largely bottlenecked. Under such circumstances, support failures in four representative coal mines in China are selected as research objects, through which dominating implied principles are investigated and re-clarified by field observations. In the Datong coal mine, an extremely fractured roadway is successfully maintained by simply changing the end-encapsulated bolting system to a fully bonded bolting system, with the results indicating the formation of an artificial compressive stress arch. In the Kongzhuang coal mine, a deep-buried shaft with a super-large section is effectively stabilized by tieback cable bolts, and a 561-day-long load-monitoring procedure verifies the effectiveness. In the Donghuantuo coal mine, the support ideology of retaining, reinforcing, and holding functions is presented to interpret bolt support failure under an aqueous environment. In the Hulusu coal mine, 5400-mm-span entries are stabilized by simply installing four tendons on the roof; the effectiveness is further proven, and an enhanced beam building mechanism is interpreted. At the end of this study, the effectiveness of a pretension force, a fully bonded bolting system, longer tendon support, and mesh/shotcrete is discussed. All of the examples given in this study are proposed to meet the principles of high efficiency, low cost, and operational friendliness. Additionally, the authors hope that through this paper, more comprehensive research/analytical methodologies will be able to bridge support theories and applications, which is the main purpose of this work. Image 1 • Field observations of support failures were carried out in some representative coal mines in China. • Implicit mechanisms behind specific failure patterns were revealed by refining existing theories. • Mainstream support ideologies were discussed, and experience was reiterated and emphasized. [ABSTRACT FROM AUTHOR]