Development of a New Ring Shear Apparatus for Investigating the Critical State of Sands
The present study investigates the shearing behavior of sands pertinent to liquefaction and critical state soil mechanics using an improved ring shear apparatus designed and constructed at the University of Illinois. Undrained/constant volume and drained triaxial compression and ring shear tests (sheared to about 30 m of shear displacement) were performed on two clean sands and one silty sand. Shear displacements localized when the peak friction angle was mobilized and subsequent shear displacements occur only within the shear band which was (10--14)xD50 thick. Considerable particle damage and crushing was observed within the shear band, particularly for dilative specimens, which led to volumetric contraction in the shear band. The critical state line (corresponding to the critical state after particle damage and crushing was complete) was much steeper and plotted below conventional critical state lines in e -- log sigma' space measured using triaxial tests. Both dense and loose sands reached this final state. Accordingly, two definitions of critical state of sands with and without particle damage are proposed.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign