Experimental analysis of the influence of drainage board diameter coefficient on sludge treatment combining horizontal drain-vacuum preloading with geomembrane bags

In the combined method of horizontal drainage board vacuum preloading and sealed geomembrane bags, the horizontal drainage board serves as the sole drainage channel, making its diameter coefficient critical in determining the appropriate filling height. Based on the theoretical model for vertical drainage boards, this study analyzes the influence range of a horizontal drainage board using the sealed geomembrane bag method. Model tests show that the maximum influence diameter coefficient of the horizontal drainage board lies between 24.6 and 25.3. By referencing the minimum influence diameter coefficient typically used for vertical drains, the applicable range for horizontal drainage boards in sealed geomembrane bags is suggested to be 15.0 to 25.3. Results also reveal that the upper slurry layer drains more efficiently than the lower layer due to gravity-assisted downward flow. In contrast, upward drainage in the lower zone is less effective. Adding a drainage board at the bottom creates a direct flow path and improves consolidation in the lower zone. To mitigate clogging during testing, the drainage board was embedded in geotextile, which reduced clogging to some extent. However, as clogging is difficult to avoid in practice, the proposed coefficient does not account for its effects.