Determination and influence of the unified strength theory parameter for loess

The parameter b of the unified strength theory was set to depict the contribution of the intermediate principal stress on the failure of materials. A large number of true triaxial tests were carried out to determine the values and variation in the parameter b for loess, with which the effect of b on the estimation of the stability for a typical loess slope was then studied. The unified strength theory could be applied to fit the experimental failure loci of loess better than the traditional strength theories. The value of the parameter b greatly depends on the stratum age, remolding state, dry unit mass (dr) and water content (w) of the loess, and the appropriate value decreases with increasing dr and w. The value of b for the undisturbed Malan loess (L1) is much greater than that for the Lishi loess (L2). Comprehensively, the range of b = 0.2–0.5 is recommended to obtain the empirical value of the loess, with which the factor of stability (FOS) for the loess slope can be estimated with a 5–15% increase compared to that when applying the Mohr–Coulomb failure law.