A Rock Mass Classification Method for Tuff Tunnel Based on the High-Pressure Gas Expansion Method

Table 4

Tunnel rock mass classification for HPGEM.

Rock mass grades	(MPa)		Quantitative indices (BQ value)
	150∼100	0.86∼0.7	637.2∼554
	100∼60	0.7∼0.55	554∼417.5
	60∼30	0.55∼0.4	417.5∼290
	≥150	≥0.86	≥637.2
	≤30	≤0.4	≤290