EFFECT OF END PLATENS ON MICROSTRUCTURE EVOLUTION IN DILATANT SPECIMENS

ABSTRACT: End platen conditions are known to affect the global response of triaxial specimens during laboratory testing of soils. For example, these effects lead to barrel-shaped specimens in axial compression tests with associated difficulties in determining cross-sectional area and stress distributions. This paper presents the results of a study that used optical analysis of images captured from resin impregnated specimens at various global axial strain levels to study how internal microstructure varied as a function of the end platen conditions. Tests were performed on dilatant specimens with different slenderness ratios and different end platen configurations. The global response was quantified in terms of axial and radial strain behavior. The microstructure was quantified in terms of spatial void ratio distribution and local void ratio distribution. Analysis relating observed global response to internal microstructure evolution is presented. The results of this experimental study show that the end platen constraint is critical for microstructure evolution in dilatant specimens.

Key words: end platens, evolution, image analysis, lubrication, microstructure, non-uniformity, radial strain,specimen slenderness, void ratio distribution (IGC: D6)