For the first time, a Developing Parallel Link Excavation (DPLEX) shielded tunnelling machine, capable of accommodating circular, rectangular or horseshoe shaped cutter heads, is to be used on a railway tunnelling contract in Japan. The cutter frames make parallel link motions via crankshafts and are resistant to wear, impact shock and damage.The decentered multi-shaft is claimed to reduce cutter torque saving power consumption and enabling economical long distance drives. The tunnel will form part of the new metro system being developed by Yokohama City.
The 7.1m o.d machine, built by NKK at its Tsurumi works, will be used to dig the Honcho shield tunnel, part of the Minato Mirai (MM) 21 line project. The tunnel, being constructed by a consortium which is led by the Hazama Corporation, entails construction of a 452.9m long up-line tunnel from Kenchomae to Kitanaka (provisional) Station.
Then the DPLEX shield will be turned round to bore a 431.8m long down-line tunnel, thereby completing two single-track tunnels.
The new MM21 metro line, extending 4.1km is scheduled to begin service in 2003.