Abstract
In cold regions, saturated fractured rock is prone to crack initiation, extension, and branching along the original fracture end under the effect of freeze-thaw (F-T) cycles and cyclic fatigue loadings. The resulting strength deterioration is accompanied by large amounts of pore growth, which results in localized damage and fracturing along the crack end and even causes overall failure. To study the fatigue damage behaviors of fractured rocks under F-T cycles and cyclic loadings, single-joint quasi-sandstone specimens with joint angles of 45° and 90° were prepared. Subsequently, F-T damage tests with 0, 10, and 20 cycles and cyclic loading tests with different stress levels were performed. The F-T damage features are discussed based on the binarization image of localized damage along the joint ends and their wave velocity variations. It is found that the frost damage of single-joint quasi-sandstone tends toward a strip with localized fatigue characteristics. Moreover, the changes of strain compliance and dissipated energy are studied under the effect of loading-unloading fatigue. Some of the interesting phenomena observed are as follows: (i) during the early stage of cyclic loading, the joint can be compacted; nevertheless, it tends to expand along the fracture direction once it passes the elastic stage, and the irreversible plastic deformation is stable at this stage. (ii) The cracks caused by F-T damage in the 45° single-joint samples deflect along the fracture direction, in contrast to the 90° single-joint specimens. Moreover, the samples with a 45° single joint are more susceptible to original fracture at the early stage of the failure process, which results in a different failure mode from that of the 90° single-joint samples. (iii) The F-T cycles and cyclic loadings have a coupling effect on the single-joint sandstone. The strain compliance and hysteresis energy keep increasing uniformly after the F-T cycles and cyclic loadings.
Highlights
The frost-heave effect is an important issue for many environmental and engineering problems in the permafrost region (Pei et al, 2019)
Few reports exist on the damage mechanism and fracturing process of fractured rocks in cold regions
F-T tests of 0, 10, and 20 cycles are performed on the water-saturated single-joint sandstone samples; see Figure 2B
Summary
The frost-heave effect is an important issue for many environmental and engineering problems in the permafrost region (Pei et al, 2019). During freeze-thaw (F-T) cycles, fractured rocks in cold regions are prone to localized damage and fracture failure along the crack end, which is essentially a problem of fatigue damage by repeated frost-heaving forces and melting (Ruedrich et al, 2011; Jia et al, 2015). It is necessary to carry out an experimental study of cumulative fatigue damage and tip fracture evolution of fractured rocks under F-T cycles and periodic loadings, which has practical significance for the understanding and the evaluation of the long-term stability of fractured rock damage in cold regions. To explore fatigue deformation and tip fracture of fractured rocks, Yang et al (2017) carried out cyclic loading tests on prefabricated double-fractured rock and analyzed the initiation, expansion, and penetration process of a crack group under cyclic loadings. Under the combined action of F-T cycles and cyclic loadings, different failure modes of fractured sandstone were observed at different angles
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