Hazard assessment of groundwater inrush in crushed rock mass: an experimental investigation of mass-loss-induced change of fluid flow behavior

Groundwater inrush induced by collapse columns in crushed rock mass is a significant problem in deep mining operations. A change of fluid flow behavior is an important key to understanding inrush processes, especially regarding particle migration and mass loss. We conducted fluid-flow experiments on crushed mudstone to investigate the effects of mass loss on flow behavior in crushed rock. We consider initial porosity and Talbot power exponent as the two main influencing factors. The results indicate that particle migration leading to mass loss is the main reason for the flow change from non-Darcy seepage to turbulence, which then induces groundwater inrush. Upon an abrupt reduction of pore pressure, the inrushing water flow rapidly increases and the fluid flow change occurs with violent flushing. We apply the experimental results and statistics to discuss and assess groundwater inrush hazards using a proposed criterion related to the rate of mass loss (mp′). The groundwater inrush hazard of the studied samples is classified as low if mp′< 10 gs⁻¹ m⁻³, medium if 10 gs⁻¹ m⁻³≤mp′