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Large section tunnel in-situ expansion excavation is prone to induce ground settlement, posing a threat to the service safety of surrounding structures. However, the settlement evolution of the overlying strata during tunnel expansion excavation are not yet clear. A method combining theoretical analysis, physical model testing, and engineering practice was adopted to investigate the settlement evolution of the overlying strata during expansion excavation of tunnels. A theoretical model for tunnel expansion excavation settlement was established. The research findings indicate that the settlement of the overlying strata above the tunnel exhibits a sudden increase characteristic, with the expansion excavation settlement zone showing a parabolic distribution, which is primarily related to the cohesive force of the rock mass and its brittle fracture characteristics. The strata settlement shows a nonlinear increasing relationship with the distance from the tunnel, mainly influenced by the non-uniform attenuation of excavation unloading disturbance. The theoretical model curves can reflect the settlement evolution consistent with the physical model tests, with an average deviation of 4.8% between the experimental and theoretical values. Considering the influence of the correction coefficient α for tunnel support on the measured engineering values, the model with α=0.7 and α=0.4 can better predict the range of surface settlement after tunnel expansion excavation and support. The research results provide a theoretical method for calculating strata settlement during tunnel in-situ expansion excavation.
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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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