Studies have indicated that the shear strength of soils is influenced by the intermediate principle stress. Generally

the shear strength of soils is correspondent with Mohr-Coulomb criterion under the condition of compression and extension in triaxial tests; but in the condition of three-dimensional stresses

soils have a higher shear strength

and the failure points on π-plane are beyond Mohr-Coulomb criterion. Based on true triaxial tests

this paper proposes an angle of equivalent internal friction and a failure criterion for cohesionless soils. The criterion can take into account the influence of intermediate principle stress. Compared with the results of true triaxial tests

it is found that this failure criterion is better than Mohr-Coulomb criterion. It is promising that the failure criterion can be applied to the cohesive soils in the future.