Research Article
Instability Process of Crack Propagation and Tunnel Failure Affected by Cross-Sectional Geometry of an Underground Tunnel
Table 3
The loading plan for physical experiments.
| | Number | Section shape | Loading (MPa) | Initial load | Maximum load (MPa) | Loading method | Excavation pattern |
| | T1 | Horseshoe | 4.94
5.40
5.52
6.06
6.30 | 2.17RC | 2.77RC | After excavation, the load is applied to the maximum load step by step, and the load is maintained at 10 min for each stage | The whole section of the tunnel is excavated. Completed in four steps. Each excavation is of 100 mm. Speedy driving. | | T2 | Circular | 4.94
5.43
5.50
5.56
5.84 | 2.17RC | 2.56RC | | Number | Section shape | Pressure stability time (min) | Initial load | Maximum load (MPa) | | T3 | Horseshoe | 8
18 | 2.47RC | 2.47RC | | T4 | Circular | 4
23
240 | 2.35RC | 2.35RC |
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Rc is the uniaxial compressive strength of model material, 2.28 MPa.
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