The present work takes one deep mine repairing project of rectangular crossheading at fully-mechanized caving workface as the background. Based on both the theoretical analysis and experimental implement, the failure zone and evolution law of the surrounding rock around crossheading are achieved. The main influencing factors can be regarded as the magnitude and direction of initial rock stress, the current goaf status of the adjacent workface, mining stresses, rock properties, geological structure and groundwater, respectively. Large surrounding rock deformation, roof falling, rib spalling and asymmetric deformation are treated as the failure sign. The depressurization, reinforced support and yielding pressure supporting principles are proposed in the end, which the supporting scheme is applied along with the FLAC evaluation to guarantee the accuracy. The engineering application shows that the proposed supporting parameters are reasonable and effective.
With the development of deep mining (Liu, Q., et al., 2004), gas leakage, rock blasting, high mine pressure (Wan, Y., et al., 2006), big crossheading strain, hard crossheading repair and the increasing maintenance rate (Ren, J., et al., 2014), the stability and supporting technique of deep crossheading surrounding is currently an urgent issue (Wang, F., et al., 2016), which already causes the worldwide attention (Yang, X., et al., 2013).
Due to the stress concentration of rectangular crossheading excavation, rocks around the crossheading gain large deformation (ZHANG, X., et al., 2004), and may even triggered roof fall, floor heaving and rib spalling (Li, D., et al., 2009). These problems seriously restrict the excavation speed (Wang, M., et al., 2016), which directly impact the safe and efficient exploitation of mine construction (Zhang, L., et al., 2014). At the same time, the huge maintenance rate arise from improper supporting not only bring tremendous loss, but also get the whole mine in trouble, or even worse shut down (Fu, J., et al., 2004). It is one of the key problems for the deep mining development and safety excavation to solve the problem of rectangular crossheading supporting technique in deep coal seam. Therefore, it is necessary to analyze the failure properties of the surrounding rock around rectangular crossheading and put forward a reliable repairing support technique in deep thick coal seam, which is of great significance to realize the safety production of the coal mine.
The mine is located about in northwest of Binxian 20km away, which belongs to Xianyang city of Shaanxi province. The depth of the coal seam is 600m, the maximum thickness of coal seam is 26.2 meters, which owns an average thickness of 14.49 meters. As a deep thick mine, initial stress of the crossheading is high. Coal tends to possess the same characteristics of soft rock under high stress, which results in large deformation. Taking advantage of the fully mechanized sublevel caving method, the mining crossheading has obvious dynamic pressure along with the workface stoping, which aggravates the deformation and instability of the crossheading. The specific performance is large floor heave in crossheading mining. The deformation of transportation crossheading is also serious, which lead to the failure of supporting system for the initial roadway. The roof sinks, rib spalls, influencing zone expands, which seriously affects the normal safety production. The formation parameters are shown in Table 1.