Volume Reduction Method for Dredged River Sediment: A case of using a High-pressure Mechanical Dehydration System

摘要

Currently a wide-scale project is underway in Hyogo and Osaka Prefectures to modify and reinforce seashores and rivers against storm surge disasters and other such flooding. The Kanzaki River, a Yodo River tributary, is a waterway targeted by the project, and our firm was assigned the task of dredging its bottom for purposes of river improvement (channel preservation).In this project the dredging work was carried out by a backhoe-dredge, and the plan called for the dredged sediment to be transported by small barges to Phoenix Amagssaki Offshore Landfill Site for disposal. However, material dumped at the site had to meet certain standards enacted to support the site's future use as reclaimed land. Specifically, the material had to provide sufficient trafficability (i.e., a 15-ton bulldozer can travel over it), with strength rated at a minimum cone index of 400 kN/m2, and it could not be alkaline. Moreover, we needed to come up with a sediment processing method mat would extend the usable life of the disposal site.As the dredged sediment did not meet those criteria without some form of processing, we chose to employ a high-pressure mechanical dehydration system (4 MPa filter press) that not only generates soil wim ample strength, but also excels at volume reduction.By using this system, we were able to sustainably process the dredged material into cakes with strength stabilized at an average cone index of approximately 1,000 kN/m2, amply surpassing the disposal site's soil strength standard. Furthermore, we succeeded in reducing the material to about 56% of its original excavated volume. As a result, the system helped to extend the lifetime of the disposal site, a feat unachievable by processing methods that rely on sotidifiers.