Rock strength parameters from classification and testing - Geotechnical Investigation and Design Tables - page 72

Table 6.9 Rock classification.

Rock type Descriptor Examples Allowable bearing

capacity (kPa)

Igneous Acid Granite, Microgranite 800-8000

Basic Basalt, Dolerite 600-6000

Pyroclastic Tuff, Breccia 400-4000

Metamorphic Non foliated Quartzite, Gneiss 1000-10,000

Foliated Phyllite, Slate, Schist 400-4000

Sedimentary Hard Limestone, Dolomite, Sandstone 500-5000

Soft Siltstone, Coal, Chalk, Shale 300-3000

6.10 Rock strength from slope stability
•

The intact strength between different rock types is shown.

•

For this topic, the tables that follow are used to illustrate the relative strength.
However this varies depending on the reference used.

Table 6.10 Variation of rock strength (Hoek and Bray, 1981).
Uniaxial compressive

Strength Rock classification

strength (MPa)

Sedimentary Metamorphic Igneous

40 Lowest Phyllites

50 Clay - Shale

60 Dolomites

⏐

70 Siltstones Micaschists

80 Serpentinites

100 Quartzites

110 Sandstones Marbles

120 Pegmatites

140 Granadiorites

150 Granites

170 Highest Rhyolites

6.11 Typical field geologists rock strength
•

Another example of rock strength variation, but with some variations to the
previous table.

6.12 Typical engineering geology rock strengths
•

Another example of rock strength variation, but with some variations to the
previous table.