Page 168 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

136 Engineering Rock Mass Classification

TABLE 10.3 Characterization and Rating of the Joint Alteration Factor

Term Description jA

A. Contact between rock wall surfaces

Clean joints

Healed or welded joints Softening, impermeable filling 0.75
(quartz, epidote, etc.) 1

Fresh joint walls No coating or filling on joint surface, 2
except from staining (rust) 4

Alteration of joint wall 3
4
i. 1 grade more altered The joint surface exhibits one class
higher alteration than the rock

ii. 2 grade more altered The joint surface shows two classes
higher alteration than the rock

Coating or thin filling

Sand, silt, calcite, etc. Coating of friction materials
without clay

Clay, chlorite, talc, etc. Coating of softening and cohesive
minerals

B. Filled joints with partial or no contact between the joint wall surfaces

Type of filling Description No wall contact
material Partial wall contact (thick filling or
(thin filling <5 mm*) gouge)

Sand, silt, calcite, Filling of friction material 4 8

etc. (non- without clay

softening)

Compacted clay “Hard” filling of 6 6–10
materials softening and cohesive
materials

Soft clay materials Medium to low over- 8 12
consolidation of filling

Swelling clay Filling material exhibits 8–12 13–20
materials clear swelling properties

*Based on joint thickness division in the RMR system (Bieniawski, 1973).
Source: Palmstrom, 1996, 2000.