Critical state behaviors of unsaturated soil in the direct shear test under constant pressure

In this paper, we examined the direct shear test results of compacted weathered granite specimen for the critical state behavior. In the direct shear test, an opening was set between the upper and the lower shear boxes before the shear process. In the analysis, the principal stresses were decided based on several hypotheses for Mohr's stress circle, and Cam clay type stress parameters were defined. From the test results, the maximum volumetric compression point (M.C.P) line was defined as the critical state line. The volume change behaviors towards the critical state were also observed in comparison with the critical state line obtained by the triaxial test. Moreover, the existence of Hvorslev surface was verified by applying the equivalent stress (p _e′) from the normal consolidation line. Above all, these results show that the critical state behaviors can be recognized in direct shear test.