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To investigate the influence of normal stress on the seepage and damage characteristics of sandstone during dynamic constant-amplitude cyclic direct shear, red sandstone samples were subjected to dynamic constant-amplitude cyclic direct shear tests under normal stresses of 10, 15, 20 and 25 MPa. During the loading process, acoustic emission (AE) signals were simultaneously recorded, and the permeability of the sandstone was measured in real time. After testing, the fracture surfaces of the sandstone samples were scanned using a 3D scanner. The test results indicate that the permeability evolution of sandstone during direct shear exhibits distinct stage characteristics, which can be described as “gradual decrease→slow decrease→slight recovery→exponential increase.” Throughout the loading process, the permeability of samples subjected to high normal stress consistently remains lower than that of samples under low normal stress. As the normal stress increases, the initiation of AE activity in the samples is delayed. However, the Felicity effect occurs earlier and more prominently, indicating a greater extent of damage. Higher normal stress facilitates a transition in the fracture mode of sandstone from tension-dominated to shear-dominated. At the microscopic level, increased normal stress promotes the development of transgranular cracks, leading to straighter crack propagation paths. Simultaneously, crack propagation is restricted near the main shear plane, ultimately resulting in macroscopically flatter fracture surfaces with lower roughness.
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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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