Drained and Undrained Strength Interpretation for Low-Plasticity Silts

The engineering behavior of low-plasticity silts is more difficult to characterize than is the behavior of clay or sand. Due to their tendency to dilate during shear, establishing a consistent and practically useful failure criterion for low-plasticity silts can be very difficult. Consideration of how the undrained shear strength of silt is related to changes in pore pressure provides a more useful and practical framework for understanding the undrained strengths of these materials and for characterizing undrained strengths for practical purposes. Using a value of Skemptonʹs A as a failure criterion has been found to result in very reasonable values of undrained strength and to reduce scatter in the results as compared to using other criteria. Using a failure criterion based on an appropriate value of A results in consistent values of Su/p, and tolerably small values of strain at failure. For low-plasticity, dilative silts that pose the greatest problems with respect to definition of "failure," using A=0 as a failure criterion is an appropriate and simple choice.