Influence of anisotropy on yielding and critical states of an unsaturated soil

A programme of controlled suction triaxial testing was performed on unsaturated and saturated samples of speswhite kaolin prepared by two different methods of compaction: isotropic and anisotropic. Tests involved probing stress paths, to investigate the initial forms of the yield surface for isotropically compacted and anisotropically compacted samples, and how the yield surface was altered by stress paths involving plastic straining. Tests also included shearing to failure, to investigate critical state conditions. The results suggest that critical states are unaffected by differences of initial anisotropy or by subsequent changes of anisotropy. Critical states can be represented by a series of parallel critical state lines in the deviator stress-mean net stress plane or by a single critical state line in the deviator stress-mean Bishop’s stress plane. Similarly, constant suction cross-sections of the yield surface can be represented by different forms of distorted ellipse in the deviator stress-mean net stress plane or the deviator stress-mean Bishop’s stress plane