Gateroad entries provide access to the operating face in longwall coal mines. These entries are subject to significant changes in the vertical and horizontal stress caused by stress redistribution around the approaching longwall panel. Estimating the required support for these extreme conditions is difficult because the rock is typically in a post-peak loading condition associated with large deformations. This paper presents a conceptual model of support loading and deformation caused by longwall-induced stress changes that is based on in-mine monitoring studies and numerical modeling results. The conceptual model is based on the principle that the volume of the detached roof that may collapse during a roof fall represents the load that must be controlled by the support system. The model also considers the fact that stress-driven roof deformations are essentially irresistible and support systems should ideally yield without shedding load. An example is provided in which the effect of roof dilation on roof reinforcement and standing supports is evaluated and the ability of the system to control the deadweight load of the detached roof strata is assessed. The conceptual model can be used to develop an understanding of likely support performance during the design of longwall gateroad support systems.
Gateroad entries provide access to the operating face in longwall coal mines. These entries are subject to significant changes in the vertical and horizontal stress caused by stress redistribution around the approaching longwall panel. The stress changes can exceed the rock and coal mass strength, resulting in large deformations of the excavation walls. Consequently, extreme support methods are implemented that may combine both internal rock reinforcement and external standing supports to maintain safe working conditions. Figure 1 shows a deformed gateroad in a U.S. coal mine that has been supported and re-supported using various types of strata reinforcement and standing supports. The support system is required to accommodate the essentially irresistible deformation of the surrounding rock that is driven by the longwall-induced loads, while preventing the collapse of the yielding roof strata.
Methods of estimating the required support density for coal mine excavations include empirical methods, based on statistical analysis of case histories (Mark, 2000; Stone, 2016), analytical models based on beam theory (Frith and Colwell, 2010; Canbulat, 2011), numerical-model-based analysis (Seedsman, 2013, Gale and Fabjanczyk, 1993), and ground response curve analysis (Barczak et al. 2003, Barczak et al., 2008, Esterhuizen and Barczak, 2006)..