Monotonic Behavior of Mississippi River Valley Silt in Triaxial Compression

The static behavior of Mississippi River Valley silt was characterized using triaxial compression testing. Silt specimens, especially overconsolidated ones, showed dilation behavior. There was no unique critical state among specimens with different overconsolidation ratios (OCRs). With OCRs of 1, 2, and 8, the specimens exhibited normal behavior and dilated more as effective consolidation pressure dropped. However, for an OCR of 4, the specimens showed opposite behavior and dilated more as effective consolidation pressure rose. The friction angle of the silt was computed on the basis of several failure criteria, and the limiting strain was found to be the best one owing to better consistency and rational results of the friction angle. The silt showed a unique behavior compared with sand and clay: The critical state line was not parallel to the normal consolidation curve in the e-lnp(') space; the stress-strain behavior can be normalized by effective consolidation pressure. The normalized shear strength of overconsolidated specimens was correlated to that of a normally consolidated specimen using Ladd et al.'s equation with an m value of 0.58 for low-plasticity silts. However, the normalized shear strength of overconsolidated silts cannot be related to OCR directly. It was indicated that at least the normalized shear strength of a normally consolidated specimen needs to be tested for low-plasticity silts to obtain the normalized shear strength of overconsolidated specimen using Ladd et al.'s equation. DOI: 10.1061/(ASCE)GT.1943-5606.0000603. (C) 2012 American Society of Civil Engineers.