A 5.17m diameter Herrenknecht Mixshield TBM started the second of three drives on Stage 2, Phase 2 of the Kai Tak Transfer scheme in Hong Kong, following the first breakthrough in early September.
China Harbour/Transfield JV made the first of three breakthroughs after previously tunnelling through two foamed concrete backfilled lower shafts along the alignment following initial launch at the first shaft.
The TBM has completed 1,030m of 1,420m through highly variable ground conditions, including completely decomposed granite (CDG), full-face slightly decomposed granite, alluvium and CDG with corestones beneath the streets north of the old Kai Tak airport. The JV claimed the Mixshield has proved effective for settlement control in areas of low cover, utilities and mixed faces of rock and soft ground.
The TBM has only 370m of excavation left, but two additional major challenges remain. Firstly the TBM will be turned through 90 degrees and re-launched from a jet-grouted NATM chamber for a short 90m drive with low cover while operating on flexible “umbilical” lines, allowing the back-up to be “left” behind in the first drive. Secondly, following completion of this drive, the TBM will be removed and re-launched in the opposite direction from the starting shaft for a 280m drive, which is also complicated by low cover and utilities below an existing road.
The use of a Mixshield TBM in variable ground conditions for controlling settlement, the use of flexible “umbilicals” for the TBM launches from shafts, NATM-driven headings in soft ground and shotcrete-lined permanent works shafts are considered firsts for Hong Kong.
UK-based Pigott Shaft Drilling (PSD) supplied the slurry treatment plant with support. China Harbour/Transfield JV said the system proved effective at separating the varying ground conditions and has been very reliable.
China Harbour Engineering Company is a state-owned Company who has long-term involvement in the Hong Kong construction industry. Leighton Holdings subsidiary, John Holland Pty Ltd, owns the construction arm of Transfield Holdings.
