Rate-Dependent Fracture Properties of Concrete–Rock Interfaces under Natural and Saturated States

To evaluate the safety and stability of the concrete gravity dams constructed in earthquake-prone areas, this study investigated the rate-dependent fracture properties of concrete–rock interfaces in both natural and saturated states. Initially, direct tensile tests were performed across a wide range of strain rates, ranging from 10−5 to 10−2/s to measure the tensile strengths of concrete–rock interfaces under natural and saturated states. Subsequently, three-point bending tests were performed within the same range of strain rates to measure the fracture properties of concrete–rock interfaces under natural and saturated states. The findings demonstrated significant rate dependence in the mechanical and fracture characteristics of concrete–rock interfaces under natural and saturated states, and the rate dependence under the saturated state is more sensitive than that under the natural state due to the viscous resistance effect induced by the free water. Tensile strengths, fracture energies, and initial fracture toughness presented a positive correlation with the logarithms of strain rates. As the strain rates increased from 10−5 to 10−3/s, the tensile strengths in the natural and saturated states increased by 71.79% and 152.36%, respectively. The fracture energy in the natural and saturated states increased by 29.52% and 59.80%, respectively. The initial fracture toughness in the natural and saturated states increased by 41.48% and 41.20%, respectively. In addition, the characteristic lengths of the concrete–rock interfaces exhibited a clear decreasing trend as the strain rates rose, indicating an increased brittleness of the concrete–rock interface at higher strain rates.