<p>The stress concentration of the hole defect significantly impacts the mechanical properties of high-performance concrete (HPC) members in deep underground environments. Prior to the flow of pressurized liquid into the crack through the hole, confining pressure exerted by the pressurized liquid restricts the crack propagation. However, once the pressurized liquid enters the crack through the hole, it nullifies its confining effect on the crack. This study presents a novel experimental comparison scheme to investigate how the pressurized liquid flowing into the hole affect HPC’s mechanical properties. In this experimental scheme, one type of the sample is completely isolated with the pressurized liquid; while for another type of the sample, the pressurized liquid can only contact the inner surface of the hole, but cannot contact other surfaces of the sample. Experimental results demonstrate that the pressurized liquid flowing into the crack through the hole alters both the stress–strain curves and the failure mechanisms of the HPC specimens. Notably, there is no primary tensile fracture initiated from stress concentration zones around holes in either sample type; instead, shear fractures dominate their failure mechanisms. The influence of the pressurized liquid flowing into the hole primarily manifests as vertical tensile cracks generated from the compressive stress concentration areas surrounding the hole. Furthermore, the flow of the pressurized liquid into the hole weakens the triaxial compressive strength of HPC, and the Newman failure criterion is modified to predict the triaxial compressive strength of HPC with a hole in both conditions. </p>