Properties of cement-treated soils in Trans-Tokyo Bay Highway project

Abstract

Four types of ground improvement by cement-treatment were used for the Trans-Tokyo Bay Highway project, which is now under way. In the first two methods, either a slurry mixture of sand, cement and sea water with some clay or a mixture of sand and cement in a rather dry state is produced in a vessel. The ‘slurry’ mixture was placed underwater using tremmie pipes, to construct fill embankments. Anti-segregation chemical adhesive was added to the ‘dry’ mixture immediately before placing underwater by using a special large diameter chute. In the other two methods, existing soft clay deposits were mixed in situ to considerable depths with cement slurry having either a high or a low cement content. The strength and deformation characteristics of undisturbed samples were obtained from test fills, and full-scale fill embankments constructed using cement-treated sand and existing soft clay deposits improved by mixing in situ with cement slurry. They were tested by an advanced triaxial testing method. Axial strains for a range less than 0·001% to about 1% were measured locally. The elastic stiffness obtained from triaxial tests using the least disturbed samples was comparable with that from field seismic surveys. Strength and stiffness of these cement-treated soils are similar to those of typical natural sedimentary soft rocks.