ABSTRACT
In a city that is attracting attention from around the world as “INZAI” due to its increasing concentration of data centers, TEPCO Power Grid, Inc. had constructed tunnels for laying underground power lines in a very short period to increase supply capacity and to meet the rapidly increasing demand for electricity. To achieve both process security and face stability in a highly collapsible sandy ground, a Dual Mode TBM which is a combined Slurry and earth-pressure-balance type TBM was adopted, and four TBMs were used simultaneously to accomplish high-speed construction. This paper will explain the construction results of tunnels with outer diameters of 4.45 m and 5.3 m and a total length of 10.1 km in just 484 days with a maximum speed of 1.2 km per month by using four TBMs at the same time. Furthermore, the outline of the Dual Mode TBM, the switching method between slurry mode and earth-pressure-balance mode and the excavation data and analysis results before and after the switching will also be described.
