Experimental investigation and image-based analysis of clay slurry consolidation with prefabricated horizontal drain

Abstract The characteristics of the consolidation facilitated by prefabricated horizontal drains (PHDs) combined with vacuum loading, and the evolution of the soil column surrounding the PHDs, which significantly affects the acceleration efficiency, remain insufficiently understood. This study conducts experimental investigations into PHD-assisted consolidation, employing an enhanced digital image correlation (DIC) technique. A novel texture seeding method for slurry, essential for DIC measurements, was developed and applied to consolidation model tests with varying PHD pave rates. Data on vacuum-discharged water reveal that the consolidation rate increases with the pave rate, albeit non-linearly. The DIC-observed plane strain fields exhibit distinct non-uniform features, with zones closer to the PHD consolidating significantly faster than other regions. The shape of the soil column observed through the DIC method is approximately elliptical, and its dimensions are characterized using empirical equations, highlighting the feasibility of optimizing PHD spacing in engineering design. The void ratio distribution was derived from strain information, validating the findings related to the soil column. Additionally, excess pore pressure distributions suggest that the effective range of vacuum transfer lies between 20 and 30 cm. Water content and undrained shear strength distributions provide key insights into the non-uniformity of PHD-improved consolidation. Further studies are recommended to quantify the optimal pave rate and the effective transfer distances of vacuum pressure and incorporate the observed soil column information into PHD-assisted consolidation analysis.