Management of the Soils Discharged from Shield Tunnel Excavation

This paper presents a case history where about 950,000 m3 of the excavated soils (or construction sludge) generated from Hanshin Expressway shield tunnel construction site was properly managed and reused as reclamation material. Three challenges existed to proceed this entire project. First, separated tunnel and reclamation projects were firmly connected. Reclamation was planned and conducted to fill an area of 8.3 ha which was previously used as an old lumber yard and expected to be an industrial space. The entire project connected a series of highway construction generating the excavated soils and land reclamation project. This type of project was the first attempt in Japan. Second, ICT (information and communication technology) based on the electronic toll collection (ETC) system was applied to manage the soils. In this project, the ETC manifest system was developed and operated to secure traceability concerning the transportation of a large amount of excavated soils. This system improves the efficiency of issuing manifests, minimizes traffic congestion, and avoids overloaded vehicles. Third, to avoid adverse subsidence of land and facilities adjacent to the reclamation, several countermeasures were conducted, such as improvements of reclaimed and original grounds as well as consideration of reclamation procedure. Excavated soils were subjected to soil improvement to obtain sufficient mechanical properties as reclamation material at a soil improvement plant installed at the site next to the reclamation site. Gypsum-based stabilizing agent was applied to secure the neutral condition in pH. A ground improvement method which is able to improve the ground under ripraps was applied to the original ground beneath the revetments, based on the numerical analysis of ground deformation.