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In order to explore the effect of freeze-thaw action on the strength and acoustic emission characteristic parameters of banded magnetite quartzite, the mechanical and acoustic emission tests were carried out on the banded magnetite quartzite with the freeze-thaw interval of[－20, 20]℃ and the longest freeze-thaw cycle of 280 times. The results show that the uniaxial compressive strength of the rock sample decreases from 200.93 MPa during drying to 106.64 MPa after 280 freeze-thaw cycles, with a decrease of 46.94%. Before and after 70 freeze-thaw cycles, the acoustic emission impact rate, cumulative impact number, energy rate and cumulative energy are significantly different in the compaction stage, elastic deformation stage and microcrack evolution stage. The damage of rock samples caused by high (period≥70 times) and low (period≤40 times) freeze-thaw cycles is obviously different. The cracks of rock samples in high freeze-thaw cycles are prone to friction, slip and extension under load, which leads to the stress redistribution of rock samples and the high degree of energy dissipation. Compared with the rock samples with low freeze-thaw cycle, the cumulative impact number, ringing count and energy of acoustic emission of rock samples with high freeze-thaw cycle in the accelerated expansion stage of micro-cracks decrease by 35.61%, 41.44% and 17.25%, respectively. The intensity of fracture of rock samples with high freeze-thaw cycles is significantly weaker than that of rock samples with low freeze-thaw cycles. With the increase of freeze-thaw cycles, the fracture characteristics of rock samples gradually change from brittle to ductile fracture, and the single b value of rock samples decreases first and then increases. The deterioration of rock samples under low freeze-thaw cycles is mainly caused by the increase of the number and scale of microcracks, while the deterioration of rock samples under high freeze-thaw cycles is caused by the penetration and merging of local fracture networks.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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