Numerical analysis and prediction of ground surface movement induced by coal mining and subsequent groundwater flooding

Ground surface movement shows different features during mining and post-mining period. If the mine goaf is dry, surface subsidence is observed in both periods. If the mine goaf is flooded by groundwater, however, ground surface uplift can be observed although much smaller in amplitude compared to the preceding subsidence. A numerical modeling strategy is proposed to predict uplift during the flooding process of an excavated coal mining area under complex geological conditions. The modeling approach considers three phases: virgin state before mining, stage immediately after mine closure, flooding phase. The model considers elasto-plastic material behavior including faults represented by interfaces. In-situ measurements are used for calibration of the model. The Oelsnitz abandoned coal mine is used for model validation and prediction. The measured subsidences up to 17 m were reproduced as well as the uplift within the last 10 years with values between 0.5-2.0 mm/year. Spatial distribution of uplift areas is well reproduced. Predictions up to the year 2051 show an increase in uplift velocity between 0.5-3.0 mm/year and additional total uplift of up to 300 mm.