EXPERIMENTAL STUDY ON SWELLING CHARACTERISTICS OF BENTONITE BUFFER MATERIAL CONSIDERING VARIOUS INITIAL CONDITIONS

Abstract

Swelling pressure tests have been conducted to determine the swelling characteristics of bentonite, which is under consideration for use as a buffer material in the geological disposal of high-level radioactive waste. In a geological disposal environment, the bentonite buffer is subjected to elevated temperatures driven by the waste's decay heat, while its mechanical behavior evolves as groundwater infiltrates and saturation progresses. Therefore, a quantitative understanding of swelling behavior under coupled thermo-hydraulic conditions is essential for designing and optimizing buffer specifications. In this study, swelling pressure tests were conducted on specimens with various initial water contents and temperatures to elucidate the relationship between the time-dependent behavior of swelling pressure and heterogeneous internal state changes. These studies confirmed that there was no clear dependence of time-dependent swelling pressure on initial water content, although transient differences before equilibrium indicated its influence during saturation. Temperature minimally affected overall swelling trends but increased hydraulic conductivity. These findings quantitatively describe the thermo-hydraulic behavior of bentonite buffers and guide the design and optimization of engineered barrier systems in geological disposal.