Mechanized cross-passage construction in soft soil under high pressure: the Tuen Mun - Chek Lap Kok link – northern connection sub-sea tunnel section project, Hong-Kong
The Tuen Mun - Chek Lap Kok Link - Northern Connection Sub-sea Tunnel Section project, in Hong-Kong, involved among others the construction of two 14m tunnels, linked by emergency egress cross-passages at regular intervals. The construction of these 57 cross-passages in soft ground under high water pressure was a real challenge to the entire project, both in terms of programme and construction risks. To ensure the successful completion of these works, the Dragages HK – Bouygues Travaux Publics Joint Venture chose to develop an innovative, industrialized method to realize these cross-passages using a pipe-jacking machine, launched from one of the main tunnel tubes and retrieved in the other, inside a steel bell. This implied the definition of a multipurpose concrete tympanum, hybrid lining segments and specific methods of construction. As a result of this productioncycle-orientated approach, the construction duration of one cross-passage has been shortened to 20 days. After an introductory presentation of the concept, an overview of the many challenges raised by the development of this mechanized excavation of crosspassages, in terms of Design, Methods and Construction, is presented in this article.