| Abstrakt: |
The Central Interceptor (CI) main tunnel is a 14.7-kilometre-long, 4.5-metre-diameter sewer tunnel currently in construction under central Auckland. It will provide additional capacity in the network to meet planned population grown and development, provide a more resilient wastewater system, and mitigate west weather overflows. The tunnel runs from the Mangere Wastewater Treatment Plant, passes under central Auckland and finishes in Tawariki. It will be New Zealand's largest and longest bored wastewater tunnel. The single-pass tunnel lining is designed for a 100-year design life. It consists of 324.5-millimetre-thick concrete lining with an inner 3-millimetre high-density polyethylene (HDPE) corrosion protection layer. The thickness of concrete lining includes a sacrificial concrete layer per the client's specification. As the tunnel will be excavated through a range of different ground conditions, going from very loose sand to competent rock with an overburden ranging from 15 metres to 110 metres above the tunnel crown, several segment reinforcement types have been designed for the CI main tunnel. In the area where the tunnel encounters soft ground with low overburden, three types of segments using hybrid reinforced concrete (rebar and steel fibre) are being utilised to take into account the highly variable design conditions. For the remaining alignment that is fully in rock, steel fibre reinforced concrete (SFRC) segments are being utilised. Because of the inherent uncertainty of ground conditions along the tunnel length, several strategies are being employed to align the segment type and associated design assumptions with the conditions encountered during tunnelling. This paper will discuss the challenges, lesson learned and detailed considerations in designing the tunnel segmental lining from the structural, geotechnical and constructability perspectives. Furthermore, some of the observations and lessons learned from segment production and lining installation will also be discussed, with recommendations for improvements relevant to similar future projects. [ABSTRACT FROM AUTHOR] |
