Page 373 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

328 Engineering Rock Mass Classification

TABLE 26.5 Values of the Constant mr for Intact Rock Material by Rock Group

Texture

Rock type Class Group Coarse Medium Fine Very fine

Sedimentary Clastic Conglomerate Sandstone Siltstone Claystone
(22) 19 9 4

Greywacke
(18)

Non- Organic ---------- Chalk ----------

clastic 7

---------- Coal ----------
(8–21)

Carbonate Breccia Sparitic Micritic —
(20)
limestone (10) limestone

8

Chemical — Gypstone Anhydrite —
16 13

Metamorphic Non-foliated Marble Hornfels Quartzite —
9 (19) 24

Slightly foliated Migmatite Amphibolite Mylonites —
(30)
25–31 (6)

Foliated* Gneiss Schists Phyllites Slates
33 4–8 (10) 9

Igneous Light Granite — Rhyolite Obsidian
33 (16) (19)

Granodiorite — Dacite —
(30) (17)

Diorite — Andesite —
(28) 19

Dark Gabbro Dolerite Basalt —
27 (19) (17)

Norite — ——
22

Extrusive Agglomerate Breccia Tuff —
pyroclastic type (20) (18) (15)

The values given are estimates. It is suggested to get the mr values from triaxial test data.
*These values are for intact rock specimens tested normal to bedding or foliation. The value of mr will be
significantly different if failure occurs along a weakness plane.

Source: Hoek, Marinos, and Benissi, 1998.