Transparent Soils Wiki

Silica Powder

 

Grid under glass dish

Fig. 1 — Grid under glass dish viewed through 5 cm thick specimen of transparent soil 

The first family of transparent soils was made of precipitated amorphous silica powder commonly used as filler to manufacture paint, cosmetics, and paper. Fluids made of mineral oil and solvent or calcium bromide brine have been used as matching pore fluids.  Specimens are typically consolidated from a de-aired slurry made by mixing amorphous silica and the pore fluid (Fig. 1).   Amorphous silica powder is a commercial product of PPG, Inc., used without further processing. It consists of ultra-fine particles with individual diameters on the order of 0.02 m (Fig. 2). These particles combine to form larger porous aggregates. Amorphous silica is well suited for producing transparent claylike material because it is hygroscopic, thereby adsorbing pore fluid and dis- placing air.

Amorphous silica Powder
 SEM image of Amorphous Silica particles
Fig. 2 — Amorphous silica Powder (LHS), and SEM image of Amorphous Silica particles (RHS)

Amorphous silica is suitable for modeling strength, permeability, and consolidation behavior of low-plasticity natural clays (Fig. 3). Amorphous silica powder has been used to study flow near wick drains  and in 2D tank tests.  A wide range of foundation problems have been investigated including pile penetration, deformations near penetrometers, helical anchors, ground improvement using sand columns , and in centrifuge tests to model the behavior of suction-embedded plate anchors.

Triaxial test results  
  Fig. 3 — Typical triaxial test results on samples of amorphous silica
 
  

Primary References

  • Liu, J., Iskander, and S. Sadek (2003). Consolidation and permeability of transparent amorphous silica, Geotechnical Testing J., Vol. 26, No. 4, pp. 390–401, ASTM [link]
  • Iskander, M., J. Liu and S. Sadek (2002). Transparent amorphous silica to model clay. Journal of Geotechnical and Geoenvironmental, Vol. 128, No. 3, pp. 262-273, ASCE [link]
  • Sadek, S., M. Iskanderm and J. Liu (2002). Geotechnical properties of transparent silica. Canadian Geotechnical Journal. Vol. 39, No. 1, pp. 111-124, NRC Research Press [link]
  • Iskander, M., J. Lai, C. Oswald, and R. Mannheimer (1994). Development of a transparent material to model the geotechnical properties of soils. Geotechnical Testing Journal. Vol. 17, No. 4, pp. 425-433, ASTM [link]