Laponite has emerged as a particularly promising material for use as a soft clay surrogate in geotechnical modeling, as it provides a relevant range of transparency, plasticity, and overall geotechnical behavior. This paper presents an investigation of the significant factors affecting the transparency of laponite for its use in physical geotechnical models. Image analysis techniques and complementary optical tests were conducted to gain an understanding of the factors causing changes in optical clarity. Aging time, laponite content, and rheological additive dosage were found to be the most significant factors affecting the transparency of laponite. Specifically, the ratio between the rheological additive dosage and laponite content (additive mass ratio) was found to serve as a relevant index to define the material’s optical behavior, and its use facilitated the determination of the optimum laponite and additive contents. The presence of inclusions within the internal laponite structure, such as trapped air pockets and unhydrated laponite crystals, identified as the key factor compromising optical clarity, could be ultimately associated with the selection of insufficient dosages of rheological additive. Overall, laponite was identified as a viable surrogate of natural clays suitable for models requiring comparatively large in-depth visualization.
The use of so-called “transparent soils” as proxy geotechnical materials has allowed for the nonintrusive observation of a variety of models representing different engineered systems. Laponite is one such soft clay surrogate that has seen increased usage in recent years. However, this material has yet to be subjected to a thorough characterization and quantification of its physical and mechanical properties. The study presented herein followed a systematic approach toward the characterization of Laponite RD colloids from a geotechnical perspective across a wide range of mixes and additive dosages. Rheology tests were conducted to study the variation in apparent viscosity with time and after remixing. These tests identified two sources/types of strength gain: a reversible thixotropic strength gain and an irreversible particle aggregation strength gain. Different mixtures tested in a one-dimensional consolidation oedometer showed that mixes with laponite colloid contents as high as 21 % could be achieved from mixes with an initial colloid content of 11 % by mass. Finally, results from vane shear tests showed that the undrained shear strength increased with: (1) increasing laponite colloid content, (2) decreasing additive dosage, (3) aging time, and (4) increasing temperature. The base geotechnical characteristics and mechanical properties of the clay surrogate as provided in this study are expected to facilitate proper interpretation of the behavior of this surrogate material in geotechnical physical models involving transparent clays.
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