Table 5 Tunnel support strategies.
Level | Color | Basis of judgment | Support Strategy |
---|---|---|---|
I | Scarlet | extremely high stress, very high PGA | metal mesh—bolts—high prestressing anchor cable—shotcrete |
II | Red | high stress, high PGA | metal mesh-high prestressing bolt-anchor cable- shotcrete |
III | orange | medium to high stress, high PGA | metal mesh-high prestressing bolt- shotcrete |
IV | Yellow | medium stress, medium PGA | metal mesh + bolt |
V | Green | low stress | bolt |