Objective To accelerate ecological protection and high-quality development in the Yellow River basin, the concept of “conductivity, storage, and utilization” has been proposed to achieve the mine water storage and protection by transforming goafs into underground reservoirs and utilizing waterproof concrete dams. However, under the action of long-term water immersion and mining activity, the interfaces of composite concrete dam structures might undergo strength degradation, leading to hidden hazards.

Methods By incorporating 0.5% and 1.0% nano-SiO₂, -Al₂O₃, and -TiO₂, this study prepared specimens with one vertical interface each that comprised double semi-cylinders through casting twice. Then, through non-metallic ultrasonic detection and uniaxial compression experiments, this study investigated the variations in the interface stability and strength of nano-modified concrete specimens with interfaces after water immersion.

Results and Conclusions The failure of the specimens with vertical interfaces exhibited two stages: interface rupture and complete failure. This finding reveals the staged failure mechanisms of the specimens with vertical interfaces under compression. After 14 days of water immersion, normal specimens showed average decreases of 19.15% and 15.11% in complete failure strength and interface rupture strength, respectively. This result indicates that the water immersion environment produced a deteriorating effect on both the complete failure strength and interface rupture strength of the specimens. The analysis of the failure characteristics of the specimens reveals that only the unimmersed specimens mixed with 0.5% nano-TiO₂ exhibited shear failure through the interfaces, while the remaining specimens showed splitting failure parallel to the interfaces. This finding demonstrates that the incorporation of 0.5% nano-TiO₂ could enhance the resistance to shear of the interfaces. However, such enhancement was weakened by water immersion. Compared to normal specimens with vertical interfaces, those mixed with 0.5% nano-TiO₂ presented an increase of 35.23% in interface rupture strength, suggesting a significant enhancement in the interfaces. In contrast, the specimens incorporating 0.5% nano-SiO₂ exhibited an increase of 37.14% in complete failure strength, implying a generally high performance in matrix enhancement. The specimens incorporating 0.5% nano-SiO₂ showed the greatest improvement in elastic modulus and deformation modulus, which increased by 30.34% and 39.25%, respectively. The results of this study hold significant scientific value and provide essential engineering guidance for the long-term safe, stable operation of underground water reservoirs and related engineering facilities.