Effects of a simulated gap on anisotropic swelling pressure of compacted GMZ bentonite

Abstract

Gaomiaozi (GMZ) bentonite is a promising buffer material for Chinese high-level radioactive waste (HLW) disposal, and will be either compacted in situ or used as dense prefabricated material when constructing engineered barriers. Uniaxial compaction can induce anisotropy of the bentonite structure, resulting in anisotropic swelling. In this work, a series of swelling pressure tests were performed on compacted GMZ bentonite to investigate the anisotropy of its property and highlight the dry density effect. Two kinds of technological gaps were simulated to analyze the change in anisotropy of properties with limited swelling deformation. The relationship between swelling pressure and dry density was found to be logarithmic, and axial pressure increased more rapidly than radial pressure with dry density. The ratio of radial to axial pressure decreased significantly in the dry density range 1.395 Mg/m3–1.706 Mg/m3; beyond this, it remained at about 0.76. For the swelling volume ratio of less than 16.7%, the stable swelling pressure was controlled by the final dry density. For a larger swelling volume ratio, the axial gap induced a smaller swelling pressure compared with the case of no gap at the same final dry density.