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)