Safety Threshold Determination for Blasting Vibration of the Lining in Existing Tunnels under Adjacent Tunnel Blasting

Table 10

Statistics of the relationship between the PPV and the change in the healthy state of the lining.

Rock grade	Number of blasting vibration velocity distributions						Crack grade		Change in crack
	V ≤ 3 (cm/s)	3 < V ≤ 5 (cm/s)	5 < V ≤ 6 (cm/s)	6 < V ≤ 7 (cm/s)	7 < V ≤ 8 (cm/s)	8 < V ≤ 10 (cm/s)	Before	After
III	103	31	2	1	2	—	B∼1A	B∼1A	Crack width increased
IV	31	10	1	—	—	—	B∼1A	B∼1A
III	73	48	1	1	—	—	B∼1A	B∼1A	Crack length increased
IV	10	9	1	—	—	—	B∼1A	B∼1A
III	31	33	10	—	—	—	B∼1A	1A	Crack grade reduction