CEMENT-MIXED SOILS IN TRANS-TOKYO BAY HIGHWAY PROJECT

The focus of this paper is on the significant role of several soil-cement-mixing technologies employed in Trans-Tokyo Bay Highway project. The two major issues are the large scale improvement of existing soft clay deposits by cement-mixing in place controlling the strength, and the construction of large offshore embankments by the underwater placing of slurry type cement-mixed sand at the ramp sections controlling the strength and density, and dry type cement-mixed sand at flat places of one of the man-made islands. These issues are described in relation to the construction of the world's largest diameter shield tunnels and a huge offshore diaphragm wall. A new method to determine the design strength of cement-mixed soil for limit equilibrium stability analysis was developed based on CD and CU triaxial test results. Advanced laboratory stress-strain tests contributed greatly to the geotechnical design and construction control. The importance of accurate measurements of small strain in triaxial tests to obtain relevant design parameters is emphasized. The strength and deformation characteristics of cement-mixed soil encountered in this project are summarized. It is shown that they are comparable with those of natural sedimentary soft rocks which support a number of important heavy infra-structures allowing a limited amount of ground deformation.