THE CRITICAL STATE OF SANDS

There is conflicting evidence regarding the critical state and steady state of sands. It seems that in some cases the critical state and steady state are taken to be equal and in others they differ significantly. The steady state is shown to be dependent on stress path, initial fabric and initial density in some cases and not in others. This Paper examines a fine to medium, uniformly graded quartzitic sand. The critical and steady states are shown to be equal and independent of stress path, sample preparation method and initial density. Data suggest that the critical state friction angle in sands may be a function of the critical state void ratio. The steady/critical state line is shown to be non-linear, and to have a marked increase in slope at stress levels greater than about 1000 kPa. The critical or steady state point must be selected from triaxial test data with care to ensure that pseudo-steady states are not compared with true steady states. Test procedures and the intrinsic properties of the material being tested must be controlled well. The overall scatter in the steady/critical state line for the sand studied is +/- 0.01 in terms of void ratio at stress levels less than 1000 kPa. For real sands with variable intrinsic properties, the scatter may be much larger.