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 ratio ν and unit weight of rock γ
Rock strength | Types of rock (examples) | Strength σc [MPa] | Poisson's ratio 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 | 0.10 | 28.00 - 30.00 |
Highly hard rock | very hard granite rock, quartz porphyry, very hard granite, hard flinty shale, quartzite, very hard sand rock, and very hard calcite | 100 - 150 | 0.15 | 26.00 - 27.00 |
Hard rock | granite, very hard sandstone and calcite, quartzite 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 | 23.00 - 24.00 |
Soft rock | shale, soft limestone, chalk, 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 - 2 |