Abstract
The shear-strength anisotropy of loess-paleosol sequences (LPS) provides vital information for engineering and construction activities and mitigation against geological disasters. The shear-strength anisotropy of undisturbed and disturbed samples from a profile from Xiushidu village, Jingyang County, in the Chinese Loess Plateau, and the formation mechanisms of such anisotropy were studied through direct shear tests and the microstructural analysis of their characteristics. Our results suggest that the shear strength of loess layers L1, L2, L3, L4, and L5 along the vertical direction was greater than that along the horizontal direction, under different values of axial compression. Under the same vertical pressure, the shear strength along the vertical direction was also generally greater for the layers above the seventh paleosol layer (S6), while the opposite result appears in the layers below S6. For the disturbed samples, their anisotropic characteristics are the same as for the undisturbed samples. The microstructure characteristics, including skeleton particles, contact relations, pore forms, cementation degree, and pore area ratio (PAR), explicated the reasons for the anisotropy of shear strength. Moreover, the influence of PAR, porosity (n), and dry density (ρd) on the shear strength in the vertical direction are greater than that in the horizontal direction, and the influence of water content is opposite to that of PAR, n, and ρd. Gravity, van der Waals forces, and hydrogeochemical reactions play important roles in the shear-strength anisotropy of the LPS. Therefore, research on the anisotropy of shear strength contributes to increasing our understanding of such layers, in preventing and mitigating against potential geological disasters and in implementing more appropriate engineering construction techniques.
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