Effects of Water Saturation on the Mode I and II Fracture Behaviors of Rock–Concrete Interfaces Under Static–Dynamic Fatigue Loading and Monotonic Static Loading Conditions
摘要
Concrete gravity dams are in different water-saturated states when in different zones, and they may be subjected to various complex loads during their operations. To investigate the influences of water saturation and loading conditions on the fracture mechanics of the rock–concrete interface, which is a weak zone of the structure of a dam, three-point bending and four-point shear fracture tests were conducted on rock–concrete composite specimens under static–dynamic fatigue loading and monotonic static loading conditions in dry, natural, and saturated states. Acoustic emission (AE) and digital image correlation (DIC) techniques were used to monitor the entire fracture process of the interface in real time. On the basis of the experimental results, the mode I and II fracture characteristics of rock–concrete interfaces with different water saturation states were systematically analyzed. The entire damage–fracture process and the crack propagation behavior of the interface were revealed. The evolution characteristics of the acoustic emissions and failure precursors of interface fractures were investigated. The water action and fatigue-induced cracking mechanisms of the interface were discussed. The results showed the following: (1) Water saturation has little influence on the interfacial crack propagation path and its failure section morphology. The distribution of aggregates in the interfacial zone and the mismatch between the material properties of the two sides of the interface are the main factors that affect the crack propagation behavior of the interface. (2) The effect of water saturation on the fracture toughness and fracture energy of the rock–concrete interface varies under different loading conditions. The initial fracture toughness and unstable fracture toughness of mode I fractures under static loading conditions for dry and saturated interfaces are lower than those for natural interfaces. However, the fracture toughness of the saturated interface at the initiation of mode II is the greatest. (3) The fatigue life of mode I and II fractures of the rock–concrete interface significantly improve with increasing water saturation level. (4) Compared with that of a natural interface, the number of AE signals produced during interfacial fracture failure processes for a dry and saturated interface decreases to a certain degree. The evolution characteristics of AE signals can provide precursor information for predicting and warning of interfacial fracture failures. (5) A dual effect of water on interfacial fracture has been identified: free water degrades mode I parameters under monotonic loading ("static weakening"), yet enhances fatigue resistance and mode II fracture performance through the Stefan effect and viscous damping ("dynamic strengthening"). The results provide a scientific reference for fracture mechanism analyses and safety assessments of rock–concrete interfaces in real working water environments.
Highlights The effects of water saturation on the fracture toughness and fracture energy of rock–concrete interfaces vary under different loading conditions. The fatigue life of mode I and II fractures of rock–concrete interfaces significantly increase with increasing water saturation. The number of AE signals produced during the interfacial fracture failure processes of a dry and saturated interface decrease to a certain degree relative to that of a natural interface. The distribution of aggregates in the interfacial zone and the mismatch between the material properties of the two sides of an interface are the main factors that influence its interfacial crack propagation behavior. Free water has both enhancing and weakening effects on the fracture characteristics of rock–concrete interfaces.