Table 5 Tunnel support strategies.

From: Failure control of large-scale exposed tunnels under the combined effects of excavation damage and dynamic disturbance at a depth of 1240 m

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