Abstract
The mechanical response characteristics of rocks under cyclic loading conditions are crucial factors for evaluating and analyzing the stability of rock mass during underground excavation. In this study, based on fractal theory and a series of tests using the MTS815.02 rock mechanics test system, the classification and fractal characteristics of limestone specimen fragments are investigated. The results show that limestone specimens subjected to cyclic loading can generate more small-sized fragments than conventional compression, but the large-fragment-producing abilities of the two tests exhibit small difference. The mass fraction of the fragments in the cyclic loading test is obviously greater than that in the conventional test when the fragment size is less than 4.75 mm; however, only a small difference is observed between the cyclic loading tests with frequencies of 0.25 and 0.5 Hz. In the same type of test, a confining pressure is helpful in reducing the fragmentation of limestone specimen. As the size interval decreases, the shapes of limestone fragment transition from rectangular to long slice and then to square. The results also indicate that the confining pressure has a significant influence on the size-quantity and size-mass fractal dimensions of limestone fragments. The former has a positive correlation with the confining pressure, whereas the latter decreases with confining pressure. The conclusions obtained in this investigation can enrich the theoretical research on the failure response and mechanism of rock under cyclic loading conditions.
Highlights
Mining, tunnel excavation, and other projects in deep mines can involve repeated loading and unloading of rock [1], which has a nonnegligible impact on the strength and longterm stability
Limestone Fragment Mass Characteristics. e mass fraction of fragments with different sizes obtained under different test conditions is illustrated in Figure 9. is figure shows that, under the uniaxial stress state, the mass fraction of specimen fragments generated in the cyclic loading test is obviously greater than that generated in the conventional compression test when the fragment size is less than 10 mm, and only a small difference is observed between the cyclic loading tests with frequencies of 0.25 and 0.5 Hz. erefore, the difference in the fragment mass fractions obtained under conventional compression and cyclic loading tests is mainly reflected in the small-sized fragments
30~50 20~30 10~20 Size interval fragments generated in conventional compression and cyclic loading tests were collected. e images of some specimen fragments are shown in Figure 11. e results show that the limestone fragments exhibit obvious classification features. e number of fragments generated by conventional compression loading is smaller than that generated by cyclic loading. e phenomenon is more apparent for the small-sized fragments. is means that the damage to limestone under cyclic loading is more severe
Summary
Tunnel excavation, and other projects in deep mines can involve repeated loading and unloading of rock [1], which has a nonnegligible impact on the strength and longterm stability. The fatigue property of rock caused by cyclic loading is an important factor threatening the safety of geotechnical engineering [2,3,4]. The mechanical behavior of rock under cyclic loading tests has been widely studied, and many valuable results have been acquired. Liu and He [5] conducted triaxial cyclic loading tests at constant amplitude on sandstone specimens. Ey found that repeated loading and unloading can weaken the rock strength and that the deformation of the specimen can accumulate cycle by cycle. Yang et al [8] conducted a series
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