STRENGTH OF ANISOTROPIC ROCK MASSES

Abstract

Mohr-Coulomb criterion is not applicable to highly anisotropic rock material and jointed rock masses. As such, taking o.2 into account, a new strength criterion is suggested because both °2 and O3 would contribute to the normal stress on the existing plane of weakness. This criterion explains the enormous strength enhancement in the underground openings because o2 along tunnel axis is not relaxed significantly. Another cause of strength enhancement is less reduction in the mass modulus reduction in tunnels due to restrained dilatancy. Empirical correlations obtained from polyaxial tests data have been suggested to estimate new strength parameters. Finally, Hoek and Brown theory is, also extended to account for a,,. The . attempt is to suggest strength criterion for supported underground openings. The effect of insitu stress, along tunnel axis, on support pressures in undrground openings has been discussed. An attempt has been made to verify the proposed polyaxial strength criterion in the insitu stress distribution.