On swelling behaviours of a bentonite under different water contents

Abstract

This study starts from a question: how would initial water content (w i ) affect equilibrium swelling pressure (p eq ) of compacted bentonites in swelling pressure tests (p s tests)? However, discussions based on experiments involving a bentonite, Kunigel V1 (K_V1), are extended to the following issues: (a) the effect of w i on p eq ; (b) pore water density (ρ pw ); (c) the co-existence of crystalline and osmotic swelling; and (d) relation between p eq and compaction tests (p c tests). It is revealed that w i has an insignificant effect on p eq in general, although a significant effect may appear for relatively high w i and dry density (ρ d ) conditions. Two swelling types, crystalline swelling with basal spacing of montmorillonite (d 001 = 1·0–1·9 nm) and osmotic swelling (d 001 ≥ ∼4·0 nm), co-exist in a w range from 36 to 65%. With the fact that ρ pw of K_V1 may range from 1·1 to 1·2 Mg/m 3 , it is expected that crystalline swelling may mainly govern p eq in p s tests if the final dry density of a specimen (ρ df ) is larger than 1·46 Mg/m 3 , while osmotic swelling may mainly govern if ρ df < 1·05 Mg/m 3 . Together with the results of p c tests, the effects of w i on p eq are explained by the proposed conceptual model.