Fig.1. Hill side failure along planar discontinuities

Fig. 2a. Portable field shear box to test rock joints (Ross-Brown and Walton, 1975)

Shear displacement

She

ar s

tres

s

Peak strength

Residual strength

Fig. 2b. Typical shear stress-shear displacement plot from direct shear test on rough rock joints

Normal stress

Sh

ea

r st

ren

gth

Residual strength

Peak strength

c

f

fr

Fig. 2c. Failure envelopes of shear strength for rough rock joint

Normal stress

She

ar s

tren

gth

(fb+i)

Failure of intact rock

Shearing on saw-tooth surfaces

Fig. 3. Patton’s simulation of asperities and bi-linear shear strength model for rock joints

Fig. 4. Barton’s shear strength model for rock joints

Fig. 5. Roughness profiles to estimate JRC (Barton and Chaubey, 1977)

Normal stress

She

ar s

tren

gth

finst

Tangent

cinst

Fig. 6. Instantaneous cohesion and friction angle for a non-linear failure criterion (Hoek, 2000)

Fig. 7. Estimation of friction angle of rock mass from RMR (Mehrotra, 1993)

Fig. 8. Estimation of Geological Strength Index (redrawn from Marinos et al., 2005)

s3

1 -3

s3=scrt

A'(s3)2

Mohr-Coulomb criterion

Modified Mohr-Coulomb criterion

sci

Fig. 9. Modified Mohr-Coulomb strength criterion

Fig. 10. Field modulus of elasticity (Mehrotra, 1992).