Effect of Seepage Differential Pressure on Permeability Evolution of Tunnel Lining Fracture under Hydraulic-Mechanical Coupling Process

The permeability evolution of lining fracture is of great significance for the safety evaluation of tunnel engineering in service. To date, there are few reports on the evolution in concrete fracture permeability when arbitrary seepage differential pressures are applied under the coupled hydraulic-mechanical processes. In this work, long-term water flow-through experiments on concrete single fractures are conducted to examine the permeability evolution during simulating the fractured lining concrete in service. Five seepage differential pressures from 0 to 350 kPa were experimentally designed, and it was found that the permeability of the fracture slightly increases by 13% at 0 kPa and decreases by 31%-77% at 70-350 kPa. The mineral dissolution of fracture surfaces during the flow-through experiments was analyzed using X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy-dispersive spectroscopy, and inductively coupled plasma mass spectrometry. Additionally, the distribution of water flow pressure within the fractures was investigated using computational fluid dynamics, and the potential occurrence of hydrodynamic impact was proposed. These studies reveal the evolution mechanism of the permeability of concrete fractures under the coupled processes, which provides an important help to the long-term safety evaluation of tunnel engineering.