Strength of Undisturbed versus Reconstituted Silt and Silty Sand Specimens

Abstract

The differences in undrained stress-strain-strength behavior between “undisturbed” and reconstituted silt and silty sand specimens tested at the same void ratio and initial stress state may be dramatic. In all tests reported herein the undisturbed specimens showed dilative and ductile behavior, whereas in all but a very few cases the accompanying reconstituted specimens at the same (or lower) density showed contraction, much lower undrained strength, and brittle behavior. The test series included samples from a natural fluvial silt deposit as well as from silty sand hydraulically placed in a tailings dam. When reconstituting specimens for laboratory testing, it is not sufficient to only satisfy the criteria of correct density and grain size distribution, but somehow the same fabric also must be reproduced. Otherwise, deformation and stability analyses based on the results of reconstituted specimens, or on in situ tests calibrated against such results, may be misleading. Most of the reconstituted specimens tested herein were prepared by moist tamping, but other methods were also used and the results compared. The reconstitution of silty sand specimens by water pluviation seems to be the most promising preparation method.