Risk of groundwater loss from an ecologically vital aquifer induced by bed separation: an assessment using strain‑softening numerical simulation

The groundwater stored in the Cretaceous strata constitutes a vital water resource for maintaining ecological stability in the Ordos Basin. This study assesses the risk of groundwater loss induced by coal mining, with particular emphasis on the influence of rock strain-softening behavior. Using the Yingpanhao Mining Area as a case study, the water-conducting fracture zone (WCFZ) was characterized using underground borehole measurements. A three-dimensional distinct-element model was developed to simulate the response of overlying strata to mining, employing both the conventional Mohr–Coulomb (MC) model and a strain-softening (SS) constitutive model. The simulation results indicate that the SS model more accurately captures progressive failure and the connectivity of plastic zones in key lithological units, including the medium sandstone within the Zhiluo Formation. The SS model predicted a WCFZ height of 124 m, in reasonable agreement with the measured height of 115.5 m. In contrast, the MC model predicted a WCFZ height of 57 m, corresponding to a relative error of 50.6%. The evolution of bed separations with increasing mining advance was also simulated, revealing four distinct separation zones. Based on the simulated WCFZ heights and protective-layer thickness distributions, a water-inrush coefficient map was generated, revealing pronounced north–south spatial heterogeneity in the evaluated water-inrush hazard, with localized areas of relatively high coefficient values concentrated in the southern region. These findings highlight the importance of incorporating strain-softening behavior when evaluating mining-induced overburden failure and provide a numerical basis for identifying areas potentially vulnerable to mining-related groundwater loss.