Direct Shear Help

[adidasmayo]

Per ASTM 3080, it states that the displacement rate should be equal to df/tf where df is the estimated horizontal displacement at failure and tf is the total elapsed time to failure. The total elapsed time to failure, tf, is equal to 50t50 where t50 is the time required to acheive 50 percent consolidation under the specified normal stress. Does this mean that prior to conducting a direct shear test one must first run a consolidation test? Is there any way to obtain general values of t50 for the type of material being tested?
Please advise.

 

[Jalthi]

Theoretically, yes you should run consolidation test. However, I haven’t seen anyone doing it. The rates I have seen vary between 0.0005 inch/min (for clay) and 0.02 inch/min (for sand).

The rate of shear should be determined such that there is ample time for drainage. Remember the test is called ‘Direct Shear Test under Consolidated Drained Conditions”.