Abstract
To explore the characteristics of rock deformation and failure under cyclic loading and unloading, the MTS815 rock mechanics test system and acoustic emission (AE) signal acquisition system were used to perform cyclic loading and unloading tests on red sandstone samples. The results showed that, compared with the uniaxial compression test, cyclic loading and unloading had a certain strengthening effect on the strength of the samples. The plastic deformation of the rock samples increased as the number of cycles increased. Based on AE signals, the cracking mode classification was analyzed on the basis of the average frequency and the rise angle of the waveforms. It was observed that the Felicity ratio gradually decreased with the increase in the stress level, which showed a cumulative damage effect. From the perspective of energy, the obvious increase of AE energy rate was mainly concentrated in the early and late stages of uniaxial compression, while the significant increase of dissipated energy rate occurred in the late stage of uniaxial compression. During the cyclic loading and unloading, most of the work done by external forces in the compaction stage and the elastic stage was converted into elastic strain energy, and dissipated energy began to gradually increase in the stage of stable fracture development. In addition, it was found that the damage evolution of the rock samples changed from slow to fast, and the dissipated energy ratio increased when failure was approaching.
Highlights
Many engineering practices have shown that the rock mass is often under an unstable state of repeated loading and unloading during engineering construction, such as excavation and reinforcement of high slopes, underground mining, and tunneling [1]
E average compressive strength of the rock samples under uniaxial compression was 74 MPa, while the average compressive strength of the rock samples under uniaxial cyclic loading and unloading was 78 MPa with an increase of 5.4% compared to uniaxial compression. e rock sample used in the test was red sandstone in the natural state, and there were inevitably original cracks inside
The cyclic loading and unloading tests were performed to comprehensively understand the deformation and strength characteristics of red sandstone under cyclic loading and unloading from the perspective of acoustic emission (AE) and energy theory. e following conclusions are obtained: (1) Compared with the compaction stage where there were only microcracks in the uniaxial compression test, the microcracks inside the samples were repeatedly closed under the action of cyclic loading and unloading, which had a certain strengthening effect on the compressive strength of the rock samples
Summary
Many engineering practices have shown that the rock mass is often under an unstable state of repeated loading and unloading during engineering construction, such as excavation and reinforcement of high slopes, underground mining, and tunneling [1]. Meng et al [21] conducted uniaxial cyclic loading and unloading compression at six different loading rates to investigate the energy accumulation, evolution, and dissipation characteristics and analyzed the stress-strain relationship and AE characteristics of the rock deformation and failure process. It remains necessary to study the AE characteristics and energy evolution laws of rocks under cyclic loading and unloading, which is helpful to explore the corresponding relationship between the damage and destruction process of the loaded rock and the AE and energy. Cyclic loading and unloading tests of red sandstone samples were performed to mainly investigate the characteristics of AE and energy evolution in the entire process of rock deformation and failure
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