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This study investigated the time-dependent crack propagation of the rock–concrete interface under sustained loading. First, sustained loading tests were performed on the composite rock–concrete beams under three-point bending with respect to three interface roughness degrees, i.e., natural, 4×4 , and 7×7 interfaces, and three sustained load levels, i.e., 80% of the maximum load, the initial cracking load, and 97% of the maximum load. Then, by employing the Norton-Bailey model and the time-dependent fictitious crack model, the constitutive relationships of bilateral materials and the rock–concrete interface were established and the mechanical responses of the rock–concrete interface under sustained loading were simulated. In addition, a crack propagation criterion proposed in this study was applied in the numerical procedure to simulate the time-dependent crack propagation process under sustained loading. The criterion implied that the interface crack propagated when the difference between the average elastic strain energy densities near the crack tip caused by the external load and cohesive stress exceeded that at the initial fracture status under quasi-static loading. The results indicated that the crack propagation under sustained loading could be interpreted from the view of energy balance between the driving energy from the external load and the resistance energy from the cohesive stress. The time-dependent crack propagation under sustained loading experienced three stages, i.e., decelerated propagation, uniform propagation, and accelerated propagation. A linear relationship between the logarithms of the crack mouth opening rate in the uniform propagation period and the failure time was established to predict the failure time of the rock–concrete interface under sustained loading. [ABSTRACT FROM AUTHOR]

This study investigated the crack propagation processes and established the lifetime prediction methods of the concrete-rock interfaces under constant loading. Firstly, the constant loading tests were performed under three-point bending loading on the composite concrete-rock beams with three kinds of interfaces, i.e. natural, 4 × 4, and 7 × 7 interfaces, and under three constant load levels, i.e. initial cracking load, 80 % and 97 % of the peak loads. Then, the clip gauge method and digital image correlation method were employed to detect the crack lengths under constant loading. Finally, the effects of constant load levels on fracture properties of the concrete-rock interfaces were analyzed and the crack propagation processes under constant loading were discussed. The results indicated that the clip gauge method was an available and accurate method to detect the crack lengths of the concrete-rock interfaces under constant loading. Crack propagation processes and crack mouth opening processes under constant loading exhibited the three-stage feature, i.e. deceleration stage, uniform stage and acceleration stage. In addition, the logarithms of the constant loading lifetimes showed an approximate linear relationship with the logarithms of the crack mouth uniform opening rates, and a quantitative relationship was established by using the linear regression analysis to establish the lifetime prediction methods. This study proposed a practical method to predict the service life of concrete structure-bedrock interface. When the crack mouth uniform opening stage was recognized, the lifetime of concrete structure-bedrock interface in service can be predicted by substituting the crack mouth uniform opening rate into the pre-established prediction model. This study can provide the theoretical support for the safety assessment of the concrete structure-bedrock interface in service. [ABSTRACT FROM AUTHOR]

To investigate the fracture property of the rock–concrete interface after sustained loading, creep tests were conducted on composite rock–concrete beams with two mechanical grooving interfaces, 4×4 and 7×7 interfaces, under two sustained load levels, 50% and 75% of the maximum load. After 90-day sustained loading, the creep specimens were unloaded and reloaded to failure in the subsequent three-point bending tests. The viscoelastic characteristic of the rock–concrete interface was numerically simulated by employing the Bailey–Norton creep law to describe the constitutive relationships of bilateral materials. Based on the numerical results, the elastic and creep strain energies within the whole specimen and the core region near the crack tip were calculated during the loading process. The results indicated that during the creep tests, the local elastic strain energy decreased due to the stress relaxation near the crack tip, and the local creep strain energy increased due to the accumulated creep strain. It was found that, at crack initiation status, the average elastic strain energy density in the core region after sustained loading was identical to that under static loading, which indicates that the elastic energy in the core region dominated the fracture behavior. Then, an energy-based fracture criterion was proposed to judge the crack initiation of the rock–concrete interface considering viscoelastic characteristics. It was found that the average elastic strain energy density of the rock–concrete interface was not affected by the viscoelasticity, which can be regarded as a material parameter. [ABSTRACT FROM AUTHOR]