Abstract: Loess is widely distributed in China and is markedly structural, differences plane strain problem exist in loess engineering. With the help of a true triaxial apparatus of Xi'an University of Technology, axisymmetric triaxial tests and plane strain test on the intact Q3 loess with different moisture contents are conducted under different confining pressures in order to study the strength evolution characteristics, the differences of strength, and failure modes. The results show that the intact loess of low water content is prone to brittle failure and the stress-strain relationship curve is softening under low consolidation confining pressure. However, with the confining pressure increasing, it hardens. Confining pressure enhances the strength of intact loess; moisture content attenuates the strength of intact loess. In brief, the failure strength of loess is closely related to moisture content, confining stress and spherical stress state. With the moisture content increasing, cohesion effect reduces obviously; while internal friction angle decreases slightly. Under the same conditions, the strength under plane strain condition is 1.1-1.4 times, larger than that under axisymmetric triaxial condition. The loess sample exhibits lateral dilatancy shear failure with single shear band under axisymmetric triaxial state, and shear shrinkage lateral dilatancy failure under plane strain state.

Key words: intact loess, axisymmetric triaxial test, plane strain test, strength characteristics, failure modes