After the Second World War, as the construction of the socialinfrastructure such as water supply and sewage systems,communications cables, railway and road net- works advanced withurban sprawl, shallow underground installations have becomecongested, necessitating the use of greater-depth undergroundtunnels. To meet this change in construction environment, we havedeveloped a new one pass lining sys- tem. This is the world's firstboltless, mechanical joint segment (NM segment) sys- tem, whichstrengthens tunnel lining materials, assures water-tightness andfacili- tates automatic segment assembly.
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