Assessment of Subsidence Hazard in Abandoned Mine Area Using Strength Reduction Method

Mine development leads to inevitable environmental consequences resulting in so called ‘mine hazard’, which occur extensively over a long period of time across a large area. The mine subsidence is considered as one of the most serious mine hazards, while the proper method is required to evaluate the mine subsidence risk. In this study, a new assessment technique to evaluate the subsidence risk in mining areas was developed using numerical and statistical analysis. Numerical simulations using FLAC2D and strength reduction method were performed to evaluate the effect of geometrical features of cavities and rock mass conditions on the ground subsidence. Based on the numerical results, the relationship between the influencing factors and the factor of safety was quantitatively obtained. It was found that the rock mass condition, height and thickness of a mined cavity has a negative effect on the subsidence while the depth and inclination of the cavity has a positive effect. The prediction model for subsidence hazard level (SHL) was proposed from the statistical regression analysis. The proposed assessment technique considered two additional important factors which were the influence area of subsidence at surface and the interaction of multiple cavities. Finally, the developed assessment technique was applied to an actual mine site to validate its accuracy. The result showed that predicted subsidence hazard map had a good agreement with the subsidence traces observed in the mine site.