Abstract: To investigate the grout diffusion mechanism in shield tail clearance, we propose a visualized test method to assess the backfill grouting’s diffusion effect using transparent soil technology. Firstly, by deriving theoretical relationships, we determined the similarity scale for each physical parameter in the model test and designed the visualized test apparatus. Next, we developed transparent slurry with a refractive index matching that of transparent soil. To gauge the adaptability of the transparent slurry, we conducted a pre-grouting test using the prepared transparent soil and slurry. Subsequently, employing our self-designed test device, we performed sensitivity analysis on three factors: tunnel depth, grouting pressure, and soil properties. The results indicate that the rheological curve of the transparent slurry conforms to that of Bingham fluid, mimicking the actual slurry diffusion pattern. Deeper tunnel burying leads to faster dissipation of slurry pressure, reduced surface settlement value within a limited distance from the tunnel axis, and less dispersion. Increasing grouting pressure leads to a decreasing grouting rate increment, facilitating easier penetration and diffusion of the slurry in poorly graded soil layers.

Key words: tunnelling engineering, backfill grouting, transparent soil technique, penetration similarity, slurry diffusion, Peck’s equation