<p>Large volumes of alkali slag are generated annually, yet its geotechnical utilization is hindered by poor dewaterability. To address this problem, three novel plastic drainage boards(X-type, Y-type, Z-type) were specifically for the vacuum preloading of alkali slag. Their reinforcement performance was benchmarked against that of an ordinary drainage board through a series of large-scale laboratory tests. Results indicate that Y-type drainage board filter membrane permeability and bending resistance is more excellent, reinforcement of alkali slag effect is the best. Compared with ordinary drainage board, Y-type drainage board increases the cross plate shear strength of alkali slag by 10.2%, reduces the average water content by 10%, and enhances the overall drainage capacity by 22.3%. Compared with X-type drainage board, Y-type drainage board construction is more three-dimensional, due to the presence of steel wire mesh, making the gap between the filter membrane and the filter element, effectively slowing down the migration speed of fine particles of alkali slag and the accumulation speed, and improving the treatment effect. In the project, it is recommended to choose the better filter membrane permeability and more three-dimensional structure drainage board for vacuum preloading.</p>