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Outline
To investigate the structural damage characteristics and deformation mechanisms of in-service metro tunnels in collapsible loess regions, this study conducted long-term structural deformation monitoring on a metro tunnel in Xi'an, China. Safety assessments of tunnel sections were performed based on monitoring data, with numerical simulations further revealing the causes of deformation in high-risk zones. The monitoring data show that the study line tunnels present a composite deformation pattern of arch subsidence and structural expansion dominated by arch subsidence. The Z5–Z6 interval was evaluated as a high-risk section due to the seriousness of the structural distress. Numerical simulations demonstrate distinct deformation mechanisms: saturation of the soil above the tunnel crown predominantly induces horizontal ovalization deformation ("horizontal egg-shaped" distortion), while saturation below the invert mainly triggers overall subsidence with minimal impact on structural dilation or surrounding rock pressure. By combining the geological investigation and deformation monitoring data, the monitored structural-expansion values match well with the predicted values for a 4-8 m flooding depth in simulation condition 3 (groundwater level rise), confirming that the compressive deformation triggered by the flooding of old loess beneath the invert is the main cause of structural deformation in this section. The findings provide valuable insights for the construction and operation and maintenance of urban rail transit systems in similar collapsible loess regions.
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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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