Failure analysis of residual coal pillar under the coupling of mining stress and water immersion in the goaf underground water reservoir

A novel fluid–solid coupling simulation method in coal weakening considering moisture content, immersion time, coal anisotropy, stress and plastic state was proposed in this paper. Based on this, the stability of the residual coal pillar (RCP) in the underground water reservoirs during longwall mining and water storage was studied by numerical simulation and field measurement. The results indicated that the RCP stress continually increased during adjacent longwall face mining, enhancing the development of the plastic zone of the RCP. However, in the following longwall face mining, there was minimal effect on the RCP. The fluid solid coupling analysis indicated that the plastic zone can develop further into the RCP until it breaks through it due to the instability of the RCP. Therefore, it is necessary to consider the effect of the instability of the RCP on the stability of the underground water reservoir.