Environmental Engineering Reference
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Figure 16.5.
Shear strength of rough clean discontinuities.
Figure 16.6.
Measurement of roughness angles (i) for first and second order roughness on a rock sur-
face (adapted from Patton, 1996).
core (Stimpson, 1981). BC Hydro (1995) recommend that the surfaces should be tested in
a wet condition to give (
b ).
The roughness angle ( i ) is generally determined by field observations of surface roughness,
at a scale appropriate to the dam foundation, in the direction of potential displacement (i.e.
the first order roughness in Figure 16.6). BC Hydro (1995) recommend that for the purpose
of dam engineering an upper bound of i
10° be applied. They also suggest that in dam
foundations normal stresses tend to be low compared to the strength of the foundation rock
so that for relatively hard (strong) rocks Equation 16.5 can be used. In soft (weak) rocks
they suggest use of Equation 16.6 with c
0.
BC Hydro suggest that the bi-linear Patton (1966) model can be replaced with the
curvilinear approach of Barton and Bandis (1991). The authors are satisfied that the
Patton (1966) approach is adequate for most situations.
a
 
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