Effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite for engineered barrier system

This study aims to investigate the effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite buffer material for engineered barrier system. Highly instrumented unconfined compressive strength tests were performed on cylindrical specimens prepared using cold isostatic pressing (CIP) technique at varying testing conditions: (a) CIP pressures of 29.43 MPa, 39.24 MPa, and 58.86 MPa, (b) specimen sizes of 30 × 60mm, 40 × 80mm, and 50 × 100mm, and (c) loading rates of 0.5 %/min, 1.0 %/min, and 1.5 %/min. As CIP pressure increases, the unconfined compressive strength (q_u), failure strain (ε_f), and elastic modulus (E) of Bentonil-WRK increase similar to Gyeongju compacted bentonite (KJ-II). Increase in diameter results in a decrease in q_u and ε_f, and increase in E. Minimal effect of loading rate was observed on q_u and ε_f. However, increasing loading rate tends to increase E. In addition, decrease in diameter increases the elastic threshold axial strain (ε_e,th). Increase in diameter and loading rate slightly increases Poisson's ratio. Prediction models are provided for assessing the effects of specimen diameter on q_u and ε_f. Furthermore, correlation models of q_u to ρ_d and E are proposed for Bentonil-WRK bentonite buffer material.