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Deformation law is of significant for ensuring the safety of structures and environment during the large diameter shield tunnelling. Particularly for shallow and large diameter shield tunnelling in soft soil, the mutual coupling of high compressibility and low shear strength of soft soil and low overburden load under shallow burial conditions as well as the unloading effect of large excavation will lead to a more complex construction deformation mechanism. Hence, the characteristics of structure vertical deformation, structure convergence deformation and surface deformation caused by shallow and large diameter shield tunnelling in soft soil and their mechanism were studied, based on the dynamic deformation monitoring of a shallow buried large-diameter shield tunnel of Shanghai Suburban Railway Airport Link Line. The results show that the ephemeral demarcation times for different deformation types were closely related. The vertical deformation of the structure can be divided into 4 stages: prior uplift, fluctuating uplift, continuous uplift, and relative stability. The structure convergence deformation can be divided into 3 stages: fluctuating convergence, continuous convergence, and stable convergence. And there are 3 stages, perturbation settlement, rapid consolidation, and relative stability in the vertical deformation of the axial surface. There are significant differences in the vertical structure deformation caused by uneven distribution of additional pressure on the tunnel structure. The maximum vertical surface deformation in the tunnel axis would exceed the warning value and the final settlement deformation would be approximately 84.3% the maximum deformation. The width of the surface sinkhole and location of the maximum settlement are closely related to the depth-to-diameter ratio, but the “swell ridge” distribution would be evident when the depth-to-diameter ratio is relatively large. In about 21~50 d after the excavation construction, the amplitude of structure vertical deformation, structure convergence deformation and surface vertical deformation is significant, and the deformation trend is relatively explicit, which is the key stage to improve the deformation control and remediation effect. The findings of this study are intended to serve as a significant reference for the control of structure deformation and environmental safety protection of shallow and large diameter shield tunnelling in soft soil.
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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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