The Long-Term Stability of a Residual Protective Coal Pillar Under High Stress States

The stability of residual protective coal pillars under high stress is the key factor that controls mining collapse and old goaf water inrush. Aiming at the problem of long-term stability evaluation of protective coal pillar in water filled old goaf, the long-term uniaxial creep parameters of saturated coal samples were measured by laboratory testing and analyzed by numerical simulation. Combined with large-scale three-dimensional stope numerical simulation, the changes in the plastic zone of a strip coal pillar subject to long-term creep were monitored. The conclusions can be drawn as follows: the water filling conditions in the old goaf weaken the mechanical properties of coal pillars, which is not conducive to the long-term stability of protective coal pillars; a Burgers model was used to fit the creep curve of saturated coal sample under high stresses, and the parameters of the constitutive model were obtained; after long-term creep of a 100-m wide saturated coal pillar under high stress states, the plastic zone expands to 40 m, and the coal pillar will be unstable under subsequent ground motion. It can be inferred that the coal pillar remains in an unstable state for a long time from the perspective of the stress field and plastic zone. The research results can provide scientific basis for stability evaluation of waterproof coal pillars under high stress states at water-filled old goaf sites.