ABSTRACT
Figure 1 shows the tunnelling problem investigated in this paper. A 6 m diameter bored tunnel will be constructed using a slurry shield Tunnel Boring Machine (TBM) passing through the lower portion of a 10 × 5 pile group supporting a 23-storey highrise building. The tunnel axis level is −23 metres Principal Datum (mPD). The segmental tunnel linings are 0.25 m thick. The geometry of the reinforced concrete frame structure building is 17.8 m wide × 8.8 m long × 70 m high, orientated perpendicularly to the tunnel alignment. The pile cap geometry is 17.8 m × 8.8 m × 1.5 m thick. The piled foundation system comprises 50 nos. of 0.6 m diameter (d) Franki piles, spaced at 3d c/c. The Franki pile is a cast-in-situ concrete pile with an enlarged base and a cylindrical shaft. The pile head and toe levels are −1.5 and −23 mPD respectively. In plan view, 15 nos. of obstructing pile toes are cut off as they intersect the tunnel. The pile toes in Column 2 and Column 1/3 are cut to a level of −19.7 mPD and −20.3 respectively, i.e. 0.3 m above the tunnel extrados.
