Set number | Characteristics and parameters of rock mass | Rating rock masses | ||||
81 - 100 (I) | 61 - 80 (II) | 41 - 60 (III) | 21 - 40 (IV) | <20 (V) | ||
1 | Rock classification | Very good | Good | Relatively good | Poor | Very poor |
2 | Average time of self supporting capacity | 10 years for active opening of 15 meters | 6 months for active opening of 8 meters | 1 week for active opening of 5 meters | 10 hours for active opening of 2.5 meters | 30 minutes for active opening of 1 meter |
3 | Cohesion of rock mass (Mpa) | >0.4 | 0.3 - 0.4 | 0.2 - 0.3 | 0.1 - 0.2 | <0.1 |
4 | Angle of internal friction | >45 degrees | 35 - 45 degrees | 25 - 35 degrees | 15 - 25 degrees | <15 degrees |
5 | Load bearing capacity (T/M2) | 440 - 600 | 280 - 440 | 135 - 280 | 45 - 135 | 30 - 45 |