Review of transparent soil model testing technique for underground construction: Ground visualization and result digitalization

In geotechnical engineering, the transparent soil (also called transparent media) technique is an effective tool for conducting experimental tests and investigating the displacement characteristics and stress distribution of soils. It plays a vital role in the observation of internal soil deformations. This study aims to briefly review the current state of some of the common materials used to formulate transparent soil models and the application of the transparent soil technique to underground construction over the last 20 years. To this end, the basic concepts of transparent soils are introduced. Then, several representative applications of transparent soil in underground construction (i.e., soil deformations induced by the penetration of pile foundations, tunnel excavation-induced movements, and structural responses caused by braced excavations) are presented. Because some research gaps may exist, certain potential research topics are proposed. This review can serve as a guideline for researchers performing experiments using transparent soils.