Transparent soils have evolved in the past two decades as a useful tool for the physical modeling of soil-structure interaction mechanisms, saturated-unsaturated hydraulic behavior, and thermal processes in soils. This paper traces the history of the development of transparent soil surrogates used in laboratory 1-g bench-scale and centrifuge tests to investigate a variety of geotechnical applications. Many notable papers that appear in this special issue of the journal on modeling with transparent soils are introduced throughout the review. The paper also looks into the future to anticipate where further advances and applications of these materials and complementary technologies may be expected.

Ground movements induced by shallow tunnels affect the safety of nearby underground and aboveground structures. Therefore, the reliable prediction of these movements is important. A transparent soil model is used to investigate not only the surface settlement profile induced by shield tunneling, but also the distribution of soil deformation within the soil mass near the tunnel. The observed surface settlements are consistent with the normal probability curve commonly used for predicting settlement, with only the inflection points or trough width parameters somewhat different. The measured data are consistent with field measurements in that the trough width parameter is independent of the volume loss and linearly proportional to the tunnel depth. An analysis of the displacement field inside the transparent soil models indicates that the subsurface settlement trough at different depths can be approximated by a normal probability curve; and the horizontal displacement can be expressed by the trough width par...

The modelling capacity of transparent soil was investigated by comparing boundary soil displacement fields under a model footing in a transparent soil model with those from a natural soil model. Transparent soil is made of either amorphous silica gels or powders and a pore fluid with a matching refractive index to model sand and clay. An optical system consisting of a laser light, camera, frame grabber, and computer was developed to optically slice a transparent soil model. A distinctive laser speckle pattern was generated by the interaction between the laser light and transparent soil. Two laser speckle images before and after a deformation were used to calculate the displacement field using an image processing technique called digital image correlation. The comparative study shows that transparent soil can be used to study natural soil with some limitations. Transparent soil and the developed optical system could be used to explore opportunities for more advanced nonintrusive three-dimensional deformation measurements for various soil–structure interaction problems.