Triaxial Mechanical Testing of Undisturbed Unsaturated Loess

We investigated the strength and deformation characteristics of undisturbed unsaturated loess under different moisture content conditions. The results showed that the deviatoric stress intensity increases with the increase of confining pressure at the same moisture content and decreases with increasing moisture content at the same confining pressure. Moreover, the matric suction and the shear strength of unsaturated loess gradually decrease as the moisture content increases. It was found that cohesion in unsaturated loess is significantly larger than that in saturated soil. Under the same moisture content, the volumetric strain decreases as the axial strain increases, but this effect is less significant as the confining pressure increases. Moreover, at the same confining pressure, the volumetric strain increases with the moisture content. Based on the theory of unsaturated soil strength, the increasing gradient of cohesion, internal friction angle, and the relationship between the shear strength and the matric suction of the corresponding soil layers were obtained. These findings provide a reliable theoretical basis for the optimal design of tunnel linings, the selection of appropriate construction methods, and the evaluation of the stability of tunnel soils during construction.