Field Study of a Sustainable Land Reclamation Approach Using Dredged Marine Sediment Improved by Horizontal Drains under Vacuum Preloading

Land reclamations often demand large quantities of fill materials. However, many countries commonly engaged in land reclamation are facing an escalating scarcity of natural fill sources. To address this issue, this study proposes a sustainable land reclamation approach that involves dredged marine sediments as fill materials. The dredged marine sediments are improved by a combined method that incorporates the use of horizontal drains with vacuum preloading for preliminary soil treatment and vertical drains with vacuum preloading for further improvement. A field trial has been designed and conducted to verify the performance of the proposed preliminary treatment of marine sediment slurry using prefabricated horizontal drains (PHDs) and vacuum preloading under a "membrane-free" condition. Field measurements, including settlement, pore pressure, effective earth pressure, vacuum pressure, water content, and undrained shear strength, were systematically recorded during the field trial period. After a four-month treatment, the average water content of the filled soil was slightly below 50%, which is one-third of the initial water content. Owing to the combined effect of the vacuum preloading and drying process, a crust layer with the undrained shear strength of 40 kPa was formed on the top of the treated soil. Below the crust layer, the average undrained shear strength of the treated marine deposits was approximately 32 kPa. Overall, the notable effect of using PHDs and the "membrane-free" vacuum preloading method to rapidly consolidate marine deposits slurry has been successfully demonstrated with field monitoring under the site trial condition.