Shear Band Formation and Strength of Loess in True Triaxial Tests

Abstract This study presents experimental results from a strength test of loess from China’s Xi’an Bailu plateau. The measurements were made with a true triaxial apparatus. Some explored characteristics were shear stress ratio, intermediate principal strain and volumetric strain changing with major principal strain, and strength criteria on the meridian and octahedral planes. The failure strength and the strain and shear band models of loess specimens were analyzed. The results clearly show shear bands in the loess specimens under true triaxial principal stresses. Softening of intact loess occurred under low confining pressure and small intermediate principal stress b-values. Hardening occurred under greater confining pressure and intermediate principal stress parameters. Structural soil mass adjacent to the shear band demonstrated a relative sliding movement and development of a shear band. The strength line on the meridian plane was linear, and the strength curve on the octahedral plane was a curved-edge-triangle shape consistent with Lade’s strength criterion. The complex pattern of the shear-band–induced failure mode is attributable to the structural characteristic of natural loess and the loading conditions.