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

Table 5

The PPV of the existing tunnel lining.

Simulated condition	Vibration direction	PPV of key point (cm/s)
		Arch crown	Blasting facing side				Blasting backside
			Arch feet	Sidewall	Haunch	Spandrel	Arch feet	Sidewall	Haunch	Spandrel
III-grade rock mass	X-direction	5.99	6.23	8.86	10.70	8.38	5.26	5.33	5.46	6.36
	Y-direction	4.63	4.45	3.95	2.25	3.66	3.96	2.64	1.66	4.13
IV-grade rock mass	X-direction	1.22	1.53	2.43	2.66	1.82	1.43	1.67	1.72	1.63
	Y-direction	1.15	0.90	0.59	0.64	1.24	0.90	0.63	0.82	1.34
V-grade rock mass	X-direction	0.98	1.01	1.87	2.01	1.31	0.97	1.22	1.35	1.01
	Y-direction	0.68	0.69	0.56	0.51	0.90	0.60	0.47	0.69	0.88