Mechanical behaviour of heavily compacted bentonite under high suction changes

Abstract

The paper reports the results of an experimental study carried out on a bentonite compacted to a dry density of up to 1·7 Mg/m3, a high value for this type of soil. The soil fabric has been studied using a variety of techniques, revealing a clear bimodal pore distribution that corresponds to two distinct structural levels: a microstructural one and a macrostructural one. The main testing programme has been performed using oedometers especially designed to apply a very large range of suctions. By applying the axis-translation technique (using nitrogen as the gas fluid), it has been possible to reach suctions up to 15 MPa. The higher suction range has been achieved by applying a controlled atmosphere where the relative humidity has been fixed by a solution of sulphuric acid or salts. In this way suctions up to 550 MPa could be reached. The maximum vertical stress that could be applied in the apparatus was 10 MPa. Two types of test have been carried out: (a) tests in which a combination of loading paths at constant suction and drying/wetting paths at constant load were applied; (b) swelling tests under constant-volume conditions in order to determine the swelling pressure and the stress path followed during wetting. The results of the experimental programme are examined, taking into account the role of the soil fabric in controlling observed mechanical behaviour. In addition, the results of the laboratory tests are reproduced and interpreted using a generalised plasticity model that considers explicitly the interaction between macrostructure and microstructure. In this way, it is possible to achieve a more complete understanding of the mechanisms that underlie observed behaviour, and in particular the interplay between the two structural levels.

Effect of thermo-coupled processes on the behaviour of a clay barrier submitted to heating and hydration

“…In the same figure, the results of the swelling pressure tests coded as SP1 and SP2 are shown. Test SP1 and SP2 are described in detail in Lloret et al (2003). The model results can be considered satisfactory, the stress path is quite well reproduced, as well as the predicted value of the swelling pressure.…”

DISCUSSION: Compaction behaviour of clay. A. TARANTINO and E. DE COL (2008). Géotechnique 58, No, 3, 199–213

“…Also represented is the total porosity of each sample that shows that, as observed by the authors, mercury filled almost all the voids at maximum applied pressure. This is not the case in compacted smectites in which a significant amount of intra-aggregate porosity too small to be detected by MIP is observed (Marcial, 2003;Lloret et al, 2003;Delage et al, 2006). Unlike smectites, kaolinite particles, made up of stacks of elementary kaolinite layers, are stable and do not change with changes in water content (Mitchell & Soga, 2005).…”

A nonlinear elastic approach to modelling the hydro-mechanical behaviour of the SEALEX experiments on compacted MX-80 bentonite

“…Instead of representing an effect of pore fluid pressure, the internal strain factor therefore represents the coupled hydro-mechanical effect of the double structure of porosity observed in bentonites and the swelling mechanism operating at different water contents (Madsen and Müller-Vonmoos 1989;Lloret et al 2003;Agus 2005;Pusch and Yong 2006;Wayllace 2008;Navarro et al 2015). Furthermore, this process is dry density dependent because the volume of macro-void space that can accommodate expanding clay clusters is reduced for a highly compacted sample in comparison with a low dry density sample (Fig.…”