Abstract
Drilling of large-diameter boreholes is regarded as an effective measure for rockburst prevention. By investigating the morphological characteristic and evolution of plastic zone in borehole surrounding rock, the pressure-relief mechanism of large-diameter borehole was ascertained, and the engineering application of large-diameter boreholes was assessed in the 13230 working face of Gengcun Coal Mine, Henan Province, China. The results showed that (1) the plastic zone in surrounding rock of borehole appear as circular, elliptical, and butterfly shapes, in which the maximum size of the butterfly wings of the plastic zone is several times larger than the borehole diameter; (2) under certain stress conditions, multiple large-diameter boreholes distributed in coal seam with rockburst risk lead to the generation and coalescence of large-range butterfly-shape plastic zone. They reduce the stress concentration and capacity for storing elastic energy of coal seam, thus reducing the rockburst risk of the coal seam; (3) large-diameter boreholes significantly decrease the stress concentration in front of the 13230 working face and improve the stress environment in the head entry, promoting the safe mining of the working face.
Highlights
Rockburst is one of the major engineering disasters caused by the violent release of accumulated strain energy in deep underground projects [1]
Jia et al [15] thought that the fundamental reason why large-diameter boreholes show the pressure-relief effect is that cracks around borehole propagate and coalesce, releasing the concentrated stress accumulating in coal seams; the pressure-relief effect of boreholes is directly proportional to the borehole diameter and depth while inversely proportional to the borehole spacing
In the case that large range plastic zones are generated and coalesce around multiple large-diameter boreholes (Figure 5), the elastic energy accumulated in the coal seam is slowly released, and the peak stress reduced as well; large pressure-relief areas are formed, and the area of stress concentration is shifted to greater depth in the coal seam
Summary
Rockburst is one of the major engineering disasters caused by the violent release of accumulated strain energy in deep underground projects [1]. In terms of pressure-relief and rockburst-prevention mechanism and the effect evaluation of large-diameter boreholes, many scholars have conducted effective studies from different perspectives. Jia et al [15] thought that the fundamental reason why large-diameter boreholes show the pressure-relief effect is that cracks around borehole propagate and coalesce, releasing the concentrated stress accumulating in coal seams; the pressure-relief effect of boreholes is directly proportional to the borehole diameter and depth while inversely proportional to the borehole spacing. By taking the specific engineering and geological conditions in Gengcun Coal Mine, Henan Province, China, as the research background, the rockburst-prevention mechanism of large-diameter boreholes was analyzed by studying the morphological characteristics and evolution of plastic zone in the borehole surrounding rock based on the butterflyshape plastic zone theory.
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