*********** 060594B.ENG *********** Country: Japan From: Brochure from UJNR Study Tour May 1994 KEYWORDS: Japan; Osaka Port, Marine Constuction, Techno-Port- Osaka +++++ THE OUTLINE AND TECHNICAL FEATURES OF OSAKA NANNKOU TUNNEL(ONT) Port of Osaka is located at the inner part of Osaka Bay and is one of the fundamental ports in the western part of Japan. Its sphere of economic influence covers the whole area of the munici- pality of Osaka and Kyoto, total of whose population reaches ten million. There are 9 container berths for foreign trade in the port. Osaka municipality, management body of Port of Osaka is working to expand port facilities such as container wharves, roads etc, and rationalize the port distribution system for increasing cargo and, in addition, is executing the Project called Techno-Port-Osaka (TPO). The aim of the TPO is to create a large new city in the coming 21st century, where one can enjoy very convenient urban living with advanced information machines as well as conduct international business, both in the South Port man-made island and the North Port man-made island which are parts of Osaka Port. In particular, Cosmosquare district in the South Port forms the core area of TPO. ONT will be the second artery connecting the existing urban area with the Cosmosquare and is supposed to contribute to solve future traffic problems caused by the development of TPO. A location map of ONT is shown in fig. 1-1. ONT is an immersed-tube type undersea tunnel, comprised of three tubes. One includes two tracks of railroad, while the remaining two tubes are for motor vehicles, two lanes each. The plane view and longitudinal cross-section figure are shown in fig. 1-2 and 1-3 respectively. The route of ONT starts at the existing subway station named Osaka Port Station and passes through the Central Pier of Osaka Port, where we have the Minatoku side portal tower equipped with tunnel ventilation machines. The immersed tunnel element portion begins from here and dives under a main navigational channel of 400m in width and 13m in depth, and reaches the edge of the South Port reclaimed land, where we have another portal tower, and, lastly, arrives at the new station called the Kaihin-Ryokuchi Station. The construction site is divided into three parts, that is Hinatoku side cut-and-cover section, immersed-tube section and Nannkou side cut-and-cover section. The method of making the immersed-tube tunnel is first, to fabricate tunnel elements in a dry-dock of a shipbuilding yard and , secondly, to float and tug them up to the site and , third- ly, sink and form them in a line at the sea bottom We show the typical cross-section of the immersed-tube tunnel in fig. 1-4. We need ten tunnel elements, about 103m in length each. Salient features of ONT are as follows. 1 Steel-concrete composite type structure is adopted as a structure of tunnel elements. This is the first time that this type of structure has been adopted in Japan. We observe that it has not been widely adopted elsewhere. 2 Flexible joint system is adopted as a mechanism of con- necting tunnel elements with each other because of large earth- quake load. 3 Steel shell caisson type structure is adopted in the construction of ventilation portal towers. 1. Hybrid structure The structure of a conventional type tunnel element is made of reinforced concrete (RC concrete) which, in general, has exterior or covering steel plate for waterproofing. We think we can utilize this steel plate as a member resisting against external load, in addition to the function of waterproofing. As a result of design calculation, although the steel plate was required to be thicker, our attempt was successful. Consequently, outer reinforcing bar could be omitted in side walls and a bottom slab of the element. (We have not yet succeeded in the case of a to slab.) Therefore, in comparison with a conventional RC structure, we can execute concrete placing into side walls and bottom slab more reliably and shorten total construction term. However, difference of cost is very small. We can ascertain th difference between a hybrid tunnel element and a conventional on from the drawing as shown in fig. 1-5. 2 Flexible joint system As there are occasionally large earthquakes in Kansai district including Osaka, it is necessary for us to conduct an earthquake resistant design. In a tunnel joint, earthquake causes both compressive and tensile stress in longitudinal axis direction and, in addition, shear stress is generated in transverse direction (both horizontal and vertical direction). We adopt the flexible joint as shown in fig. 1-6 as a joint system resistin against such loads. A rubber gasket resists against compressive force, connecting cables against tensile force, horizontal shear key against horizontal shear, and vertical shear key against vertical shear. Of course, rotation of tunnel elements occurs in the joint, however, elasticity of the rubber gasket prevent excessive stress from being generated, which would come into existence without the rubber gasket. 3 Steel shell caisson type structure for a portal tower The construction site of Minatoku side portal tower is situated at a connection of land and water area. In such a case, conventional method of constructing a portal tower is, first, to reclaim water area in the site and, secondly, perform open-cut of the reclaimed land using retaining wall, and , after obtaining enough space at a far lower level than ttiat of the surrounding water surface, building of the portal tower begins in the space. By means of this method, the portal tower can be built very accu- rately at the previously decided point. however, iL is difficult to perform open-cut of the reclaimed land against hydrostatic pressure. On the other hand, in the case of steel shell caisson type, land portion of the site is dredged, in contrast with the conventional way, and enough space in the sea is secured to accommodate a portal tower. Next, we make a rubble mound to set up the steel shell portal tower which is already fabricated in a ship-building yard and, after that, is tugged to the site. After setting up, concrete placing into tite inside of the portal tower starts. In comparison with the conventional way, this method has a disadvantage from the viewpoint of accurate setting up at a previously decided point, but, has the advantage of obtaining steady and safe execution. The real accuracy in setting up is some 10cm, while allowable limit is less than 20cm. FIGURE CAPTIONS: Fig. 1-1 Location map of Osaka Nannkou Tunnel Fig. 1-2 Plane view of Osaka Nannkou Tunnel Fig. 1-3 Logitudinal cross section Fig. 1-4 Typical xross-section of tunnel elements Fig. 1-5 Comparison between a tunnel element of RC structure and that of hybrid structure Fig. 1-6 Joint System COLOR PHOTOGRAPH CAPTIONS: Photo-1 A bird's-eye view of the site of ONP. Photo-2 Fabricating tunnel element in a dry-dock. Photo-3 Welding studs. Photo-4 Three tunnel elements before concrete placement. Photo-5 Concrete placement for tunnel element. Photo-6 Completed tunneel element Photo-7 Towing tunnel element to the tenunporary site. Photo-8 Loading test model for hybrid structure. Photo-9 Loading test for rubber gasket. Photo-10 Steel shell caison type structure of the ventilation portal tower. Photo-11 Towing a portal tower to the site. Photo-12 Concrete placement for a potal tower after setting at the site. ************** END Msg. B.ENG **************