2510109540

Fig. 5 Diaphragm wali construction by the SSS method (courtesy of Shimizu Construction Co.)

Fig. 6 Apparatus to remove gravel, part of a slurry mole (courtesy of Tekken Construction Co.)

In the urban areas, the shield method is used quite frequently. Significant improvements have been madę in the machinery and construction methods. The Japanese Railway Construction Public Corporation excavated an under-

water tunnel Crossing Morigasaki Canal near Tokyo Bay by means of a slurry mole. The shield machinę shown in Fig. 6 is capable of drilling a tunnel the outside diameter of which is as large as 7.29 meters. This equipment successfully drilled through a very soft alluvial soil and a diluvial stratum of cemented sand and clay with no blowout inci-dent. This method enables safe, continuous excavation by balancing the porewater pres-sure at the head being excavated by means of the increased supply and pressure of water to the outlet adjustment tank. For water supply, clean water may be used, and there is no need for bentenite mud.

Driving Steel pipes horizontally forms a shape of roof in the ground which counter-acts the downward earth pressures, and makes it possible to drive a tunnel beneath the pipes. Fig. 7 shows a few cross sections with pipes installed over the portion to be excavated by this method. The diameters of the pipes used rangę from 114 to 1,500 milli-meters, with the maximum length of 120 meters. Fig. 7 illustrates the construction of a subway station by this method connecting two excavated shield tunnels. This ^MSteel Pipę Roof" method has also successfully been used to drill through fault zones encountered in the Shinkansen's Kanmon Undersea Tunnel between Honshu and Shikoku.

There are many long railway tunnels in Japan. Because most of our mountains are volcanic and rocks are very often porous, a great deal of water often comes out during tunnel excava-tions, causing depletion of well water and of rice paddy water. During the construction of Haruna tunnel of Johetsu Shinkansen, wells dried up at a place 2 kilometers away from the central linę of the tunnel. Also, high-way engineers are investigating a possibility of driving a tunnel through a hot spring area where the temperaturę of the ground is as high as 100 degrees in centigrade. Dr.

Fujii's Special Lecture tomorrow will refer to some interesting problems encountered during construction of Seikan Undersea Tunnel.

Across Tokyo Bay, there is a plan to build a road which will consist of a long sunken tunnel in the central section of the road with bridges at the both ends. The length of the road is about 16 kilometers. This is going to be one of the largest civil engineering projects in Japan. There are already several sunken tunnels completed along the shores of Tokyo Bay. Fig. 8 shows one of them. Each concrete box is 37.4 meters in width, 8.8 meters in height and 115 meters in length.

Ninę boxes are connected in tandem and form an undersea tunnel, 1,035 meters in length.

Iji the project area there is a soft clay deposit, about 30 meters in thickness. A careful dynamie analysis was conducted taking into consideration the effect of strong earth-quakes, and the flexible joints were provided to connect these boxes. Fig. 9 gives part of the records taken by seismographs placed in-side the tunnel.

216