Reliability Evaluation of Water-Rich Loess Tunnel with Lining Crack Based on Extension Theory

Table 7

Comparing specification method for evaluation grading.

Grade	Crack state
I	General cracking, no development trend
II	l (length) < 5 m, b (width) < 3 mm
III	l (length) < 5 m, 3 mm ≤ b (width) < 5 mm, rapid development
IV	l (length) ≥ 5 m, b (width) ≥ 5 mm, rapid development, arch cracking was massive, may drop, and peeling