Engineering Classification of Jointed Rock Mass Based on Connectional Expectation: A Case Study for Songta Dam Site, China

Table 4

Classification standard for the evaluation index of rock mass quality [8, 10, 18].

Evaluating index	Classification grade of rock mass
	1	2	3	4	5
Rock strength (MPa)	250∼1000	100∼250	50∼100	25∼50	0∼25
Joint spacing (m)	3∼100	1∼3	0.3∼1	0.05∼0.3	0∼0.05
RQD (%)	90∼100	75∼90	50∼75	25∼50	0∼25
Roughness	1∼3	3∼5	5∼7	7∼8	8∼9
Aperture	1∼2	2∼3	3∼4	4∼5	5∼6
Weathering	1∼1.5	1.5∼2.0	2.0∼2.5	2.5∼3.0	3.0∼4.0
Groundwater	1∼2	2∼3	3∼4	4∼5	5∼7
Dip difference (°)	20∼35	5∼20	−5∼5	−20∼−5	−35∼−20