The Trans-Tokyo Bay Highway has a length of 15.1 km, of which about 4.5 km is the bridge section and about 9.5 km is the tunnel section. The tunnel was excavated by the slurry shield method. After the completion of tunnelling, the two shields facing each other were docked together under a high water pressure at the depth of about 60 m under the sea level. This paper reports the test boring, filling of high-concentration slurry, freezing and forced thawing, etc. carried out during underground shield docking. DOCKING METHOD The seabed in the work section generally has a shape of a gently curved ship bottom. Relatively solid sandy layer is deposited below the seabed. At the depth of TP-80 to 90 m or more, the sandy soil (the upper layer of the Kazusa group) having an N value of 70 or larger exists as an engineering base for design. The ground to be excavated is an alternation of diluvial sandy soil/gravel and diluvial clay. The point of underground docking is about 26 m deep from the sea level and has an overburden of 15 m. The center cutter draw-in method was selected for shield docking in view of the following points.
The structure of the shield cutter face should be simple enough to avoid breakdown during excavation.
Safety and reliability during docking should be ensured. The freezing method was used as an auxiliary method.
DOCKING PROCEDURE Underground docking was carried out in the procedure shown in Fig. 2. A. First, the first-arriving shield continues excavation until it reaches the predetermined docking position, then halts. The slurry in its chamber is replaced with high-concentration slurry. A device is attached to prevent the thrust of the late-coming shield from causing the first-arriving shield to retreat at docking time. All through the above process, the late-coming shield continues excavation.