Research on shear yield and strength failure surfaces of remold loess by true tri-axial tests

The shear strength failure surface of soil is the base of analyzing the characteristics of deformation and strength. In this paper, the tests of remold loess with different moisture contents under complicated stress condition was carried out by a true tri-axial apparatuses with a new structural cell which was developed by Xi´an University of Technology, the stress and strain curves of remolded loess were obtained under different consolidation pressures and different stress paths. The variation laws of strength failure lines under different stress paths were analyzed here. At the same middle principal stress parameter, the shear strength q_f increases with mean normal stress p. The q_f - p strength lines of remold loess with different water content pass through the same point on the p coordinate axial. In other words, the strength failure surfaces of the remolded loess with different moisture content are cone in the principal stress space. On the π plane, the points of strength failure of remold loess with same water content on the π plane changes regularly, and the strength failure surfaces of the remolded loess with different water content are similar. With increasing of moisture content, the strength curve on the π plane shrinks gradually, and the strength failure lines are similar under the different water content condition. Comparing the measured results with the strength criterion, the strength failure surface can be described by Xing Yichuan surface located at the outside of Mohr-Coulomb surface and the Matsouka-Nakai surface, and the inside of generalized Misses surface.