Effects of Strain Rate in Consolidated-Undrained Triaxial Compression Tests of Cohesive Soils. Report 1. Vicksburg Silty Clay (CL)

The results of consolidated-undrained (termed R test in Corps of Engineers nomenclature) triaxial compression tests with pore pressure measurements performed on Vicksburg silty clay (CL) are presented and analyzed in this report. All triaxial specimens were compacted with a Harvard miniature compactor to 95 percent of standard maximum density with water contents 2 percentage points wet of standard optimum. After back-pressure saturation and consolidation under four different chamber pressures, the specimens were axially loaded at rates of strain varying from 0.001 to 1.0 percent/min. The purpose of the tests was to evaluate the effects, if any, of different rates of strain on the shear strength and deformation characteristics of this particular soil. Data presented include pore pressure observations, magnitudes of deviator stresses, Mohr's diagrams, and stress path plots. R triaxial test results indicate that this lean clay, which has a liquid limit of 34, plastic limit of 22, and plasticity index of 12, is relatively insensitive to the rates of strain used in axial loading. When other materials have been tested at different rates of strain in succeeding phases of the program, more definitive guidance on rates of strain for various fine-grained soils should be possible.