| 摘要 |
<p>The tunnel driving system uses a mobile shield with stays and prefabricated rings forming arch sections, as the shield moves forward as revetment. In a first phase one or more almost complete rings of prefabricated arch sections are assembled inside the shield, keyed together and with seals round the periphery. In a second phase the shield is advanced for a distance equal to a ring width, so as to free the last ring upstream of the shield. In a third one, the last ring is expanded and provisionally keyed and sealed to the one directly upstream of it, and in the fourth it is finally keyed up.</p> |
