Abstract: Presented herein is an experimental analysis result of Xi’an Bailu Tableland loess tested by true triaxial apparatus, developed by Xi’an University of Technology, with the different consolidation pressures and intermediate principal stress parameters. The occurrence of loess shear band in cubical specimen may be related to its peak strength or the process of hardening regime. Some characteristic changes of the intermediate principal strain and volume change, and strength law on the meridian plane and octahedral plane have also been explored by the measured results of true triaxial tests. Strength, failure strains and the shear failure model of loess specimens have been analyzed to investigate the judgment basis of shear band occurrence under the condition of complex stresses. The results show that the obvious shear band appear in the loess specimens under true triaxial principal stresses, the softening behavior of intact loess occurs under the smaller confining pressure and intermediate principal stress parameters; and the hardening behavior occurs under the larger confining pressure and intermediate principal stress parameters. Consistent turning points on the curve of the intermediate principal strain and volume change with large principal strain indicate the behavior of deformation changing. Structural soil mass in the side of shear band, which is responding to the intermediate principal strain turning point, has a relative sliding and development of shear band. The strength line on meridian plane is linear; and the strength curve on the octahedral plane is a curved-edge-triangle shape that approaches to -SMP strength criterion. The complex changing of shear band of failure pattern is relating to the structural characteristic of natural loess and loading condition of different stresses.

Key words: loess, true triaxial test, shear band, intermediate principal stress, strength failure surface