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Rock Stability
Parameters Hoek – Brown
Parameter of rock breaking a
Parameter a is an exponent receiving values from 0,5 to 0,65 (for the original Hoek-Brown condition it is equal to 0,5) and depends on the degree of rock breaking.
Nonlinear parameters mb = m, s for a = 0,5
(index r denotes residual values)
| Carbonate rocks with well developed cleavage – dolomite, limestone, marble | Argillaceous rocks – mudstone, siltstone, shale, slate | Arenaceous rocks – sandstone, quartzite | Fine grained igneous crystalline rocks – andesite, dolerite, basalt, rhyolite | Coarse metamorphic and igneous rocks – gabbro, gneiss, granite | |
|
Intact rock material
Laboratory specimens have no discontinuities RMR=100 Q=500 |
m = 7.00
s = 1.00 mr = 7.00 sr = 1,00 |
m = 10.00
s = 1.00 mr = 10.00 sr = 1.00 |
m = 15.00
s = 1.00 mr = 15.00 s = 1.00 |
m = 17.00
s = 1.00 mr = 17.00 s = 1.00 |
m = 25.00
s = 1.00 mr = 25.00 s = 1.00 |
|
Very good quality rock mass
Rocks without isolated blocks, with non-weathered discontinuities RMR=85 Q=100 |
m = 2.40
s = 0.082 mr = 4.10 sr = 0.189 |
m = 3.43
s = 0.082 mr = 5.85 sr = 0.189 |
m = 5.14
s = 0.082 mr = 8.78 sr = 0.189 |
m = 5.82
s = 0.082 mr = 9.95 sr = 0.189 |
m = 8.56
s = 0.082 mr = 14.63 sr = 0.189 |
|
Good quality rock mass
Slightly damaged rocks with non-weathered discontinuities spaced from 1 to 3 m RMR=65 Q=10 |
m = 0.575
s = 0.00293 mr = 2.006 sr = 0.0205 |
m = 0.821
s = 0.00293 mr = 2.865 sr = 0.0205 |
m = 1.231
s = 0.00293 mr = 4.298 sr = 0.0205 |
m = 1.395
s = 0.00293 mr = 4.871 sr = 0.0205 |
m = 2.052
s = 0.00293 mr = 7.163 sr = 0.0205 |
|
Fair quality rock mass
Partially weathered discontinuities spaced from 0,3 to 1 m RMR=44 Q=1 |
m = 0.128
s = 0.00009 mr = 0.947 sr = 0.00198 |
m = 0.183
s = 0.00009 mr = 1.353 sr = 0.00198 |
m = 0.275
s = 0.00009 mr = 2.030 sr = 0.00198 |
m = 0.311
s = 0.00009 mr = 2.301 sr = 0.00198 |
m = 0.458
s = 0.00009 mr = 3.383 sr = 0.00198 |
|
Poor quality rock mass
Numerous weathered discontinuities spaced from 30 to 500 mm RMR=23 Q=0,1 |
m = 0.029
s = 0.000003 mr = 0.447 sr = 0.00019 |
m = 0.041
s = 0.000003 mr = 0.639 sr = 0.00019 |
m = 0.061
s = 0.000003 mr = 0.959 sr = 0.00019 |
m = 0.069
s = 0.000003 mr = 1.087 sr = 0.00019 |
m = 0.102
s = 0.000003 mr = 1.598 sr = 0.00019 |
|
Very poor quality rock mass
Numerous extremely weathered discontinuities with filling spaced by less than 50 mm, fine grained waste rock RMR=3 Q=0,01 |
m = 0.007
s = 0.0000001 mr = 0.219 sr = 0.00002 |
m = 0.010
s =0.0000001 mr = 0.313 sr = 0.00002 |
m = 0.015
s = 0.0000001 mr = 0.469 sr = 0.00002 |
m = 0.017
s = 0.0000001 mr = 0.532 sr = 0.00002 |
m = 0.025
s = 0.0000001 mr = 0.782 sr = 0.00002 |
Strength of rocks in simple compression σc , Poisson's number ν and bulk weight of rock γ
|
Rock
strength |
Types of rock (examples) |
Strength
σc [MPa] |
Poisson's number
ν |
Bulk weight of rock γ
[kN/m3] |
| Solid rock | most hard solid rock, intact, compact and dense quartz rock and basalt, other extraordinary hard rocks | >150 | 0,1 | 28,00 - 30,00 |
| Highly hard rock | very hard granit rock, quartz porphyry, very hard granite, hard flinty shale, quartzite, very hard sand rock and very hard cacite | 100 - 150 | 0,15 | 26,00 - 27,00 |
| Hard rock | granite, very hard sandstone and calcite, quarzite lode, hard conglomerate, very hard ore, hard limestone, marble, dolomite, pyrite | 80 - 100 | 0,20 | 25,00 - 26,00 |
| Rock | sandstone, ore, medium sandy shale, flagstone | 50 - 80 | 0,25 | 24,00 |
| Medium rock | hard mudstone, softer sand rock and calcite, chalky clay | 20 - 50 | 0,25 – 0,30 | 23 - 24,00 |
| Soft rock | shale, soft limestone, calk, salt rock, frozen ground, anthracite, marl, remoulded sandstone, soft conglomerate, ground with fels | 5 - 20 | 0,3 – 0,35 | 22,00 – 26,00 |
| Weak soil | compact clay, soil eluvium, black coal | 0,5 - 5 | 0,35 – 0,40 |
20,00 - 22,0
18,00 - 20,00 |
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