Codeveloped by Kajima and Hitachi Zosen, world's first three-face tunnel boring machine was used to excavate tunnel that will house new Osaka Business Park subway station.
A pioneer in the development of modern tunneling techniques in Japan, Kajima has devoted particular attention to advancing the mechanization and automation of large-scale tunneling equipment. Its latest accomplishment is the codevelopment - along with Hitachi Zosen Corporation - and commercial introduction of the world's first three-face tunnel boring machine (TBM). The huge triple-tube device recently completed excavation of a 107m-long segment of a tunnel that will house the new Osaka Business Park subway station, 32.5 meters below one of the city's busiest office and commercial centers.
Measuring 7.8 by 17.3 m, the three-face TBM enables the subway station's twin rail tubes and adjoining platform space to be excavated at the same time, thereby reducing construction time by an estimated four months over conventional tunneling methods. Moreover, the TBM successfully met various engineering challenges, including coping with difficult geological characteristics and working under extremely tight space limitations. Located directly below a skyscraper, the site is situated between two branches of a river and one of the tunnel walls is positioned just 90 cm above a major sewer line.
Tunnel Construction Process Is Fully Automated
The TBM consists of three round tunnel boring units linked side by side. As excavation proceeded in 1-m increments, three robotic assembly arms installed ductile tunnel arch segments - each weighing 2.3 tons - that formed the lining of the three circular tunnel sections, as well as specially designed 3-ton seagull-shaped segments which conencted the tubes together. Simultaneously, backfill was injected through multiple tubes set on the outer surface of the machine to stabilize the bore.
After the tunnel lining segments were secured, temporary H-shaped steel support columns were placed every meter, while permanent 9-ton columns were installed at 4-m intervals. Computer controlled placement of the columns was also accomplished by robotic manipulators. Four 3cm-diameter taps in the upper and lower seagull-shaped connector segments were aligned with holes in the permanent columns and fastened with anchor bolts, and the members were joined together working within tolerances of just a few millimeters. Beams were then place between the segments and the bearing plates on the top and bottom of the permanent columns, and the temporary columns were removed.
During excavation, individual shield cutters rotate in certain precise sequences and any adjustments for mechanical lag must be made in real time, a task which in this case was further complicated by the fact that there was three times more input/output data than for a conventional single-face TBM. Developed especially for the three-face TBM, Kajima's Comprehensive Shield Work Control System (KSGS) not only effectively controlled the complex excavation operations but also monitored face conditions for collapse, deployed mud and slurry removal equipment, and managed segment assembly.
Kajima engineers have created an advanced multimedia presentation - including computer graphics, drawings, photographs and KSGS images - for visitors to the site. Tailored to meet the audience's specific level of interest and professional knowledge, the highly acclaimed presentation has been shown to over 1,300 visitors, from professional engineers to school children.
Excavation of the tunnel began on January 12 and was completed in late April. Engineering and construction work is scheduled to be completed by the end of the year, with subway operation slated to start in late 1996.
   
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