Strength criterion of rock and effect of medium principal stress

Abstract：Drucker*.Prager criterion and Murrell criterion including medium principal stress are not verified by the results of true triaxial stresses testing thoroughly.Triaxial extension strength may be infinite in D*.P criterion outer*.joining with Coulomb criterion.The effect is too lower of minimum principal stress in D*.P criterions inner or tangent joining with Coulomb criterion, and too higher of medium principal stress.In Murrell criterion, rock can load tensile stress more than its uniaxial tensile strength, while the stress in the other two dimensions is its uniaxial compression strength.And the effect is too lower of minimum principal on the strength.

Keyword：strength criterion;medium principal stress;pseudo*.triaxial compression;triaxial extension;