Study on Instability Characteristics of the Directional Borehole on the Coal-Seam Roof: A Case Study of the Tingnan Coal Mine

Abstract

Directional long drilling on the roof is an effective gas control measure in the goaf, but there is little research on the stability of the surrounding rock. In this study, the geological conditions of the #4 coal seam in the Tingnan Coal Mine, Shaanxi Province, China taken as the application background, and the deformation characteristics of boreholes under four typical coal and rock conditions were first analyzed based on the Universal Distinct Element Code (UDEC) numerical simulation. Secondly, the stress, strain, and plastic deformation of the rock surrounding the borehole with different diameters were carried out using the Fast Lagrangian Analysis of Continua 3D (FLAC 3D). The effect of the casing on the stability of the borehole was also simulated. The results showed that the borehole stability of coal and mudstone was lower than that of fine-grained sandstone and coarse-grained sandstone. The larger the borehole diameter, the lower the stability. The borehole tended to be unstable, especially when the diameter was 160 mm and 200 mm. Traditional pipes can provide some protection, but for large boreholes, the protection is poor. Based on the above research, uniaxial compression tests were carried out on various internal support tubes, such as ‘line-shaped’, ‘Y-shaped’, and ‘cross-shaped’. The results showed that the cross-shaped pipe had the highest compressive strength, which was 4–5 times that of the other types of protective pipe and had a good protective effect. The research results can provide reliable technical support for the protection of directional boreholes on roofs through strata and have important implications for the popularization and application of the directional long borehole technique.

A Study of the Top-Coal-Drawing Law of Steeply Inclined and Extremely Thick Coal Seams in the Wudong Coal Mine

“…In recent years, in the practice for mining steeply inclined and thick coal seams, a series of mining technologies has gradually been formed. However, the top-coal-drawing rate of the fully mechanized drawing in a steeply inclined coal seam is generally low, which severely restricts the efficient production of coal resources [11][12][13][14][15].…”

Special Issue “Process Safety in Coal Mining”

“…Shuanlin Wang and coworkers [12] combined rock mechanics and fracture mechanics to analyze the influence of the shadow effect of the stress field between cracks on the evolution of equivalent stress and the plastic zone. Zhie Wang and coworkers [13] analyzed the deformation characteristics of boreholes under three typical coal-rock conditions and analyzed the stress, strain, and plastic deformation of rocks around boreholes with different diameters. They simulated the effect of casings on borehole stability.…”