Anisotropic Strength Characteristics of Loess under Three-Dimensional Stress Conditions

Abstract To study the failure conditions of anisotropic loess in the principal stress space, a series of true triaxial tests were performed on loess sampled in the Bailu Plateau of Xi’an, as loess deposits have a strong cross-anisotropic structure. The cuboid specimens of the prepared samples were cut along the vertical and horizontal directions to enable testing in any sector of the three-dimensional principal stress space. The shear strength laws of the p–q planes with different intermediate principal stress ratios corresponding to different principal stress spaces were revealed. The failure surface was assumed to be symmetric with respect to the vertical axis of the principal stress space octahedral plane, which varies as a function of the Lode angle. On the same octahedral plane, the shear strength of a specimen, as the major stress, is applied along the vertical direction and is larger than that along the horizontal direction. Failure surfaces in all sectors are ellipses, which are symmetric with respect to the vertical axis, and the loess structure is not damaged under the stress conditions of true triaxial compression. Once the structure was damaged, the failure surface of the cross-anisotropic loess on the octahedral planes presented as a circle or a curved triangle as the average principal stress increased.