Height Development Characteristics of Water-Conducting Fracture Zone in a Fully Mechanized Longwall Face with a Large Panel Width

Abstract

To explore the height development characteristics of a water-conducting fracture zone (WCFZ) in a working face with a large panel width, a typical working face with a panel width of 330 m was used as the research background for this study. The lower limit of the height of the WCFZ was preliminarily determined via borehole televiewer observation, and the maximum height of the WCFZ in the working face was further determined via numerical simulation and empirical analysis. The prediction results obtained via the traditional empirical formulas are unsuitable for working faces with large panel widths. For the studied working face, considering its actual geological background, the deformation and failure characteristics of the overlying rock under six different panel width conditions were simulated via numerical simulation, and it was found that the height of the WCFZ exhibits a good natural logarithmic relationship with the panel width. On the basis of the statistics of data collected from 58 cases of fully mechanized coal faces with normal panel widths in the North China-type coal field, the applicability of the logarithmic variation in the in situ data was analysed and compared. The accuracy of the logarithmic variation was verified by theoretical analysis, revealing that the internal factor controlling this variation is the decrease in the burial depth of the unfractured rock stratum. The case study with the panel width of the working face of 330 m extends the applicability of the abovementioned variation to panel widths greater than 300 m in North China-type coalfields, and 300 m was proposed as the threshold panel width at which the development of the WCFZ slows. This variation can provide a reference for safe mining and optimum panel width determination under high-intensity mining conditions.