A new proposed method for observing fluid in rock fractures using enhanced x-ray images from digital radiography

Fluid in rock fractures continually induces geocatastrophes in water-rock system engineering. Intuitively observing fluid in fractures is the key method for revealing the interaction mechanism of water and rock under different engineering backgrounds and providing some insights for solving engineering issues. This study proposes a visualization method for fluid in rock fractures using enhanced X-ray image digital radiography (EXIDR) and carries out coupled hydromechanical tests on the basis of the material scale of carbonate rocks, red bed mudstone (RBM) and coal. The experimental results show the transition mechanism of pipe flow (PF) to fissure flow (FF) during carbonate rock failures. The flow regime undergoes an evolution process from laminar flow to turbulent flow, which also changes with the fractal characteristics of PF-FF in carbonate rocks under multilevel stress loading. Additionally, the damage coefficient of RBM under coupled hydrodynamics and multilevel stress loading nonlinearly increases. Therefore, the initial permeability of RBM under hydrodynamics is significant for geohazard prevention in engineering and is induced by seepage and diffusion effects. In addition, the mean square flow describes how the flow rate varies with fracture growth and extension, i.e., the fractional exponential evolution relationship transitions from superdiffusion flow to subdiffusion flow. This indicates that fluid in fractures shows the dual behaviors of anomalous diffusion and nonlinear flow during coal and rock failures.