Experimental study on the shear behavior of loess and paleosol based on ring shear tests

Landslide hazards frequently occur in the Chinese Loess Plateau every year, causing devastating casualties, damage to engineering structures, and reduction in land resources. This work presents an experimental investigation of four samples retrieved from Jingyang in the southeast of the Chinese Loess Plateau, using ring shear tests and microscopic observation, in an attempt to explore the shear behavior of loess and paleosol under the larger deformations that are involved in landslide hazards. The results of ring shear tests reveal that the loess and paleosol samples exhibited different strength characteristics. The residual strength envelopes could be assumed to be a straight line, and the overconsolidated state had negligible influence on the residual shear strength. After the shear experiment, shear bands were studied from both macroscopic and microscopic perspectives. Macroscopic observation and mechanical analysis indicate that all samples developed a main horizontal failure plane related to the maximum shear stress, while loess samples also developed en echelon failure planes tilting from the horizontal at angles of 14-18 degrees, which are interpreted as Coulomb slip planes. Scanning electron microscopy reveals that the particles inside shear bands tend to be re-oriented. Particle crushing occurred in the shear process, which was also verified by particle size distribution analysis.