Density Variation in Specimens Subjected to Cyclic and Monotonic Loads

Abstract

The undrained cyclic triaxial test is widely used to evaluate the seismically induced liquefaction potential of saturated cohesionless soil. Concern that internal‐void‐ratio changes (redistribution) due to testing characteristics may render the test inappropriate for dynamic analysis is prompting research to investigate such changes. This research requires specimens with a higher degree of density uniformity than previously demonstrated. Control specimens are tested in the triaxial chamber, frozen under back pressure and confining pressure with the top drainage line open, and then dissected into 96 elements in a cold room. The density of each segment and, consequently, the density distribution of the specimen are determined from the ice content. Homogeneity, i.e., relative density uniformity, is quantified in terms of the standard deviation of all elements about the average relative density determined for the 96 elements. Relative density dispersion with an increase in strain level is shown at three densities, approximately 40, 60, and 70% relative density. Density redistribution as a result of cyclic and monotonic loading is demonstrated and quantified in test specimens of Banding sand, which is a specific gradation of Ottawa sand. It is shown that density redistribution begins at pore‐pressure responses less than 100%, but does not become significant until nearly 100% porepressure response and/or peak‐to‐peak strain levels greater than 5% are reached.