Yasunori Kondo opened his interesting talk with a brief historical resume. He reminded us that, following their first use in the UK, shield machines were introduced to Japan for the first time in 1926. Kawasaki first manufactured them in 1963. 1976 saw a turning point in their development as mechanical shields started to overtake manual shields in popularity. The eight major Japanese shield manufacturers have now recorded a staggering total of over 7000 units manufactured, ranging in size up to 14.2m in diameter.
Each new shield machine develops a little more the systems for excavation and stabilisation of the cutting face. Now, both slurry and EPB machines are close to perfection. New developments are therefore taking different directions:
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- To increase diameters and introduce automation
- To operate without departure and arrival shafts
- To minimise the sectional area excavated.
- To change the shape of the excavated face to something more user friendly.
Larger diameters
Kondo then went on to illustrate each of these development lines with some amazing examples from Kawasaki’s recent experiences.
Although the well known Trans-Tokyo Bay project used 8 x 14.1m slurry machines, three of which were designed and made by Kawasaki in its Harima factory, the first machine illustrated was a 12.04m diameter slurry shield used for an underground river diversion near Tokyo. This machine incorporated a fully robotic segment erector, which automatically took each segment from the gantry, moved it into position, picked up and inserted the nuts and bolts and then tightened them. This was achieved without any human help and a complete ring was built in about 45 minutes.
Shaft elimination
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By GlobalDataThree examples of the second line of development (machines developed to eliminate shafts) were shown. The mother and child concept uses a sacrificial rear body in which is housed the launching eye for a smaller machine driving off at right angles. The mother shield stops while the child is brought into the tunnel and launched, after which both machines can drive simultaneously.
The double stage shield is a machine with two concentric skins. After launching at the larger size of 7.3m diameter and being driven for 1.7km at this size, the outer ring of the cutterhead was removed and the inner body released. This allowed the inner section to complete the remaining 1km of drive at 5m diameter This machine was also capable of driving a 15m radius curve, quite a feat in itself.
The underground docking shields are designed to meet head to head underground and to dock allowing the central part to be removed and the lining built through. The increased cost of all these machines is justified by the saving in shaft and associated land costs they permit.
The third area of development is that of trying to reduce sectional areas by using multi-face shields in place of driving two or three tunnels. Although the triple face shield has been used before, this needs special segments, which can take some time to build. Kondo chose to illustrate this section of the talk with the H & V shield, developed by Kawasaki.
It has many of the advantages of the DOT or triple head shield but also allows the use of circular segments, reducing the time and cost of the work. The H & V shield can be used in a horizontal configuration, as illustrated by the 13.2 x 7.1m shield for Roppongi Station, or in a vertical mode, with one circular section above the other. This was shown as a 3.3m shield above a 2.9m shield as used for another river diversion project.
A further approach to this development is the use of a square shaped shield. The cutterhead of this shield incorporated two planetary cutters on eccentric links, which ingeniously excavated into the corners of the rectangular section as the main cutterhead rotated at half the speed. Although only an experimental tunnel has been driven to date, a larger version of this machine is planned for a project in Tokyo.
The DPLEX shield is yet another ingenious concept which Kawasaki is developing to alter the basic design of the cutterhead. DPLEX stands for Developing Parallel Link Excavating Shield. It operates by mounting the cutterhead eccentrically on four parallel drive shafts that rotate simultaneously. This results in the cutterhead moving in small oscillating circles instead of rotating fully. The advantages claimed are a similar movement distance for all cutting tools, allowing longer distance between tool changes and a better mixing action for EPB operations. More significantly, such a movement also allows irregular non-circular shaped cutterheads. Rectangular, elliptical or horseshoe shapes are possible.
Following a brief mention of a new microtunnelling machine that allows navigation around curved microtunnel drives, Kondo went on to discuss the position in rock TBMs in Japan. Much of the work until recently has been in smaller diameter machines and here the trend has been towards mixed mode machines. This was illustrated by a 2.3m diameter machine which can operate in open mode in competent rock or in a slurry mode when the ground is soft or fissured.
A double articulated machine which could drive around a 30m radius was then shown. This had been developed to allow the machine to drive both bores of a twin road tunnel without having to withdraw it from the ground between drives. Another 5m machine was the Improved Open 5m machine used to excavate a pilot tunnel at Rittoh. The features of this machine are that, despite being an open main beam machine, it can also install a segmental lining when the geology deteriorates, thus combining the benefits of both open and shielded TBMs.
Finally, to demonstrate that size was not a problem even in hard rock, sections of the 12.8m machine for a motorway tunnel (the Hida Tunnel) were shown. This machine is due to be works assembled in September and will start driving in spring 2000.
Kondo’s talk was brilliantly illustrated with some impressive graphics that fully lived up to the title of the talk – ÔExotic TBMs’. It was clear from the variety of questions asked that the audience was open mouthed about some of the more bizarre developments tried out and, although the answers to how these were justified financially were not fully explained, some people were left trying to find possible applications over here for at least some of the machines.
