Table 8 Classification of water outflow from tunnel excavation face.

Dry

Excavation face is completely dry

p ∈ [0, 0.01] or q ∈ [0, 5]

Wet

Wet marks can be seen in some areas of the excavation face

Moist

Water can be seen or leached from the excavation face

p ∈ (0.01, 0.1] or q ∈ (5, 25]

Dripping

Water drips from the excavation face

Rain-like dripping

There are drops of water resembling rain on the excavation face

p ∈ (0.1, 0.5] or q ∈ (25, 125]

Linear water

The excavation face has similar water pipes, and the water column is smaller (the water volume and water pressure are smaller)

Tubular water

The excavation face has similar water pipes, and the water column is relatively thick (the water volume and water pressure are very large)

p ∈ (0.5, ∞) or q ∈ (125, ∞)

Gushing water

There is a large water outlet on the excavation face; the flow and velocity are large, which often causes great damage to the project