Strain-dependent-deformation property of Gyeongju compacted bentonite buffer material for engineered barrier system

This study aims to investigate the strain-dependent-deformation property of Gyeongju bentonite buffer material. A series of unconfined compressive tests were performed with cylindrical specimens prepared at varying dry densities (pd = 1.58 g/cm3 to 1.74 g/cm3) using cold isostatic pressing technique. It is found that as pd increase, the unconfined compressive strength (qu), failure strain, and elastic modulus (E) of Gyeongju compacted bentonite (GCB) increases. Normalized elastic modulus (Esec/Emax) degradation curves of GCB specimens are fitted using Ramberg-Osgood model and the elastic threshold strain (ee,th) is determined through the fitted curves. The strain-dependency of E and Poisson's ratio (v) of GCB were observed. E and v were measured constant below ee,th of 0.14 %. Then, E decreases while v increases after exceeding the strain threshold. The Esec/Emax degradation curves of GCB in this study suggests wider linear range and higher linearity than those of sedimentary clay in previous study. On top of that, the influence of pd is observed on Esec/Emax degradation curves of GCB, showing a slight increase in ee,th with increase in pd. Furthermore, an empirical model of qu with pd and a correlation model between qu and E are proposed for Gyeongju bentonite buffer materials.