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