Rock Mass Classification for Columnar Jointed Basalt: A Case Study of Baihetan Hydropower Station

Table 5

Weak plane tightness classification.

Weak plane tightness	Tight	Relatively tight	Moderate tight	Relatively loose	Loose
Weak plane opening (mm)	<0.5	0.5~3	3~5	5~10	>10
Columnar joints opening (mm)	0	<0.5	0.5~1	1~3	>3
Geological condition	Unweathering	Slightly weathering~unweathering	Weak weathering~slightly weathering	Weak weathering	Weathering