Transparent Soil: A Review of Material Innovation, Optical Imaging Technique, and Multidisciplinary Application

Transparent soil technology has revolutionized geotechnical experimentation by enabling non-invasive visualization of internal soil deformation, seepage, and multi-field coupling processes. This paper examines recent advances across three critical dimensions on transparent soil: material development, optical observation techniques, and engineering applications. It primarily focuses on two dominant transparent soil materials (i.e., fused quartz and fumed silica), while addressing their fabrication procedures and performance characteristics. Advanced optical techniques, including laser speckle methods and 3D digital image correlation (3D-DIC), are thoroughly reviewed for their enhanced accuracy in deformation quantification. The review encompasses diverse applications spanning pile–soil interaction, slope stability analysis, seepage visualization, and thermal field monitoring, while highlighting significant cross-disciplinary potential in environmental remediation and plant root studies. Despite remarkable progress, challenges remain in standardization protocols, material cost-effectiveness, and scalability for large-scale applications. Future research directions should prioritize material optimization (particularly dynamic-response hydrogels), multi-physical field coupling methodologies, and standardized frameworks to bridge laboratory innovations with practical engineering applications. This review provides a foundation for advancing transparent soil technology toward broader implementation in geotechnical practice.