Environmental Engineering Reference
In-Depth Information
Figure 16.7.
The effective roughness angle (i) for seams (infilled discontinuities) (BC Hydro, 1995,
based on Ladanyi and Archambault 1977).
joints, shears, faults) which are persistent in the scale of the dam foundation. However for
closely jointed rock with several sets of joints not oriented unfavourably in respect to
potential failure surfaces; or for failure parallel to the base of the dam where the joints,
bedding and other defects are not oriented close to this failure surface, a Hoek-Brown
type failure criterion may be adopted. BC Hydro (1995) recommend the use of the Hoek
et al. (1995) approach:
a
m
b3
ci
s
(16.9)
1
3
ci
where m
b
a constant based on rock type; s,a
constants dependent upon characteris-
tics of the rock mass;
ci
uniaxial compressive strength of the intact rock pieces;
1
,
3
effective principal stresses.
The constants m
b
, s and a can be estimated using Hoek et al. (1995) which relates these
constants to the rock mass structure and discontinuity surface conditions.
Douglas (2003) reviewed the basis upon which the Hoek-Brown criteria determined,
and have recommended the following:
(a) The basic form of the shear strength equation remains unchanged from the Hoek-
Brown criterion.
m
3
s
(16.10)
1
3
ci
b
ci
