Page 146 - Rock Mechanics For Underground Mining

ROCK STRENGTH AND DEFORMABILITY

Figure 4.45 Relations between nor-
mal stress ( n ), shear stress ( ), nor-
mal displacement (v), and shear dis-
placement (u) in constant displace-
ment shear tests on rough discontinu-
ities (after Goodman, 1989).

Equation 4.35 suggests that there are three components of shear strength – a basic

frictional component given by , a geometrical component controlled by surface
r

roughness (JRC) and an asperity failure component controlled by the ratio (JCS / ).
n
As Figure 4.46 shows, the asperity failure and geometrical components combine to
◦
give the nett roughness component, i . The total frictional resistance is then given by
◦

( + i) .
r
Equation 4.35 and Figure 4.46 show that the shear strength of a rough joint is

both scale dependent and stress dependent. As increases, the term log (JCS/ )

n 10 n
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