Numerical Study of Failure Mechanisms and Control Techniques for a Gob-Side Yield Pillar in the Sijiazhuang Coal Mine, China

Coal pillars are formed by excavation and mining activities in an intact coal seam and play a key role in underground coal mines. Most previous investigations of pillars have mainly focused on existing coal pillar failures. However, few scholars have investigated the failure mechanisms of coal pillars during their formation process. This paper focuses on the failure of a 7 m-wide coal pillar that caused the large deformation of a tailgate in the Sijiazhuang coal mine in China. Field tests and numerical modeling were used to study the initiation, propagation, and failure of cracks within this gob-side coal pillar during its formation. Field monitoring revealed that the maximum roof-to-floor and rib-to-rib convergence reached 860 mm and 1460 mm, respectively. The coal pillar became a yield pillar with substantial fractures. A numerical model was built using UDEC Trigon logic and calibrated with laboratory tests and RQD methods. Both the natural roadway deformation and crack distribution in the coal pillar were simulated. A FISH function was used to document the propagation of shear and tensile cracks in pillars with different W/H ratios, and a damage parameter was adopted to evaluate the failure of these pillars. The results suggest that the most appropriate pillar width is 10 m. Field trials prove that a 10 m-wide coal pillar combined with optimized support measures can effectively control deformation around the tailgate.