1

1

Rock properties

2

Rock properties:

1) “Intact” rock

2) Discontinuities

3) Rock mass

2

3Hoek and Bray (1977)

“Intact rock strength”:Uniaxial Compression Test

Scale effect:

4Rusnak J, Mark C., 2002

Point Load Test(Franklin, 1973)

3

5

Triaxial test (Hoek Cell)(Hoek and Franklin, 1976)

6

Hoek-Brown strength criterion (1980)

a

cibci sm )

''(''' 3

31 ++=σσσσσ

4

7

Shear strength of rock discontinuities: Hoek field shear box

8

“In situ” direct shear test

5

9

Patton (1966)

“Multiple modes of shear failure..”

)tan( ibn += φστ

Shear strength of discontinuities in rock

10Barton, N., 1973. Review of a new shear strength criterion for rock joints. Engineering Geology, 7:287-332

Barton (1973) σc=uniaxial strength

σn=normal stress

6

11

Barton’s shear strength criterion (1973)

)](logtan[ 10n

bnJCSJRCσ

φστ +=

12

empirical Hoek-Brown strength criterion

Rock mass strength:

7

13

Uniaxial Compressive Strength

“Hammer Test”

14

mi coefficient

(measure of shear strength of the intact rock)

8

15

“Geological Strength Index (GSI)”

16

)1428100exp(D

GSImm ib −−

=

)39100exp(D

GSIs−−

=

)(61

21 3

2015

−−−+= eea

GSI

a

cibci sm )

''(''' 3

31 ++=σσσσσ

“Generalized Hoek-Brown strength criterion for rock masses

(1995)

9

17

“Rocklab” (download from www.rockscience.com)