A Stability Analysis of an Abandoned Gypsum Mine Based on Numerical Simulation Using the Itasca Model for Advanced Strain Softening Constitutive Model

An abandoned gypsum mine has been discovered beneath the route of a highway construction in Hunan province, south China. Due to the highway construction and operations safety, there is an urgent need for a comprehensive stability analysis of the abandoned mining area. The 3D laser scanning detection technique has been adopted, and over 400 drillholes were strategically placed near the highway to capture the spatial information of the abandoned gypsum mine. The ore body has an average mining thickness of about 3 m, and the depth of the mining roof ranges from 40 to 60 m, with an average span of 16 m. Based on the research achievements in the engineering geological investigation, rock mass quality assessment, and geometry information, a simplified numerical model has been established for stability analysis. The numerical model employed the IMASS rock mass constitutive model to conduct a stability analysis of the abandoned gypsum mine during the excavation process and in the medium to long term. The IMASS constitutive model can effectively reflect the entire process of rock mass from microscopic damage to macroscopic instability, and the numerical simulation of current and long-term stages provides a much greater understanding of the mining room stability and the effect of various geo-mechanical parameters not considered in traditional empirical methods. The abandoned gypsum mine stability is guaranteed in the mining and current stages. However, the numerical results showed that a 0.4 m spalling thickness of the sidewalls can cause an overall instability and failure of the abandoned mine, and reinforcement measures must be taken for long-term safety. The stability of the abandoned gypsum mine with filling solutions was also evaluated numerically.