Ground Response of a Gob-side Entry in a Longwall Panel Extracting 17 m-Thick Coal Seam: A Case Study

This study presents a comprehensive field investigation of the ground response of a gateroad subjected to high stress induced by extracting a 17 m-thick coal seam. The test site is located at Datong City, Shanxi Province, China. The measurement results of the entry convergence and fracture development indicated that the gateroad with a 30 m-wide coal pillar maintained a good performance during the development period but suffered a strong response, including roof sag, floor heave, support unit failure and internal fractures sharply developed during the current panel-retreating period. During panel retreating, the impact range of the mining disturbance was about 110 m ahead of the active panel, and the mining disturbance accelerated dramatically at 50–60 m ahead of the mining panel. The results of the borehole stress measurement showed that the maximum stress induced in the virgin coal pillar and the coal pillar reached 15.3 MPa and 23.9 MPa, which are about 1.5 and 2.3 times the initial ground stress, respectively. This high stress contributed significantly to the instability of the gateroad. The average stress within the coal pillar was greater than that in the virgin coal pillar, and a high-stress zone was found at the coal pillar depth of 11–20 m. This stress distribution characteristics implies that the 30 m-wide coal pillar has a relatively sufficient bearing capacity to withstand the majority of mining-induced loads and that the coal pillar size could be reduced from 30 to 15–20 m wide to decrease the range of high stress in the coal pillar. Furthermore, taking into consideration of intense mining disturbance and abundant time interval for gateroad development as well as a high-strength support scheme, a small-width coal pillar of 8 m was recommended and tentatively applied in the field. The field application demonstrated that the newly designed pillar size and support pattern could ensure gateroad stability at some level. The study finding can help to better understand the stability control of entry driven along gob-side and its correlation with coal pillar size as well as the mining disturbance in specially thick coal seam (ETCS). In addition, the design principle and support strategy for the coal pillar in ETCS presented in this study can potentially be applied to other similar projects.