Abstract: Loess is a typical structured soil. It is believed that the characteristics of the microstructure and the fabric of the loess could be reflected in its stressstrain relationship. Both conventional strain controlled isotropic and anisotropic consolidation undrained shear testes on undisturbed loess samples were initially conducted by the GDS triaxial testing system. A series of stressstrain relationships on the were obtained. It is observed that a typical stressstrain curve first demonstrated a steady state for a short period of time followed by a strong strainsoftening behavior. To further explore the behavior of this structured loess, a series of stresscontrolled triaxial compression tests were conducted. It is founded that the stresscontrolled triaxial tests had a better characterization of the microstructure of the loess. The structural strength of the soil is observed at the point of stress failure. Whereas, in the conventional straincontrolled triaxial tests, the constant strain rate usually could not capture the structural strength of the loess.

Key words: Undisturbed Loess Samples, Consolidated Undrained Triaxial Shear Tests, Structured Soil Characteristics, StressStrain Relationships