Objective  Concrete serves as a lining material for support structures used in vertical shafts in coal mines, and its seepage performance and mechanical characteristics play a crucial role in ensuring structural safety. Furthermore, shaft lining concrete is placed under the groundwater level, subjected to a stress environment significantly different from that of surface concrete.

Methods  To investigate the impacts of groundwater seepage on the performance of shaft lining concrete under triaxial stress conditions, hydraulic coupling tests were conducted using a servo pressure testing machine equipped with a seepage apparatus, yielding data on permeability, elastic volumetric strain, crack volumetric strain, and damage mechanics at various positions.

Results and Conclusions  The permeability evolution of the concrete experienced three distinct phases: downward, stable, and upward. The downward phase accounted for 6.93% of the stress-strain curves before the permeability peak appeared, with the permeability decreasing by 32.21% to 67.14%. The stable phase indicates that the specimens remained in an elastic state. The upward phase was characterized by an increase in the number of internal cracks, with the permeability increasing by 17.55 times at most. Using the elastic phase as a boundary, two mathematical models were constructed to describe the variations of permeability before and after the elastic phase with stress, following an exponential function and a power function, respectively. The crack initiation and damage stress points during the loading process of the shaft lining concrete were determined based on the characteristics of volumetric strain curves. As pore water pressure increased under the same confining pressure, the initial permeability increased by 48.94% on average, while the crack initiation stress, damage stress, and peak stress decreased by 5.60% on average. As the confining pressure rose under the same pore water pressure, the initial permeability decreased by16.62% on average, while the crack initiation stress, damage stress, and peak stress increased by 25.55% on average. During triaxial compression, the permeability of the concrete showed a similar evolutionary pattern to its damage progression, with the damage acceleration point appearing slightly earlier than the permeability increase point. Accordingly, a calculation model illustrating the relationships of permeability with damage and pore water pressure was developed. The results of this study serve as a significant reference for improving the multi-field coupling theory for the lining engineering of vertical shafts in coal mines and ensuring the engineering safety.