A Technical Overview of Contract No. 3801 APM and BHS Tunnels on Existing Airport Island: Jacked Box Tunnels under AEL
The provision of the new Automated People Mover (APM) tunnel connecting the expanded Terminal 2 (T2) with the Third Runway Concourse (TRC) and the new Baggage Handling System (BHS) tunnel, are key works being provided as part of the expansion of the Hong Kong International Airport (HKIA) into a Three-Runway System (3RS).The alignment of the tunnels crosses under the operational Airport Express Line (AEL) and was constructed using Jack Box tunnelling techniques. This paper presents some of the technical solutions developed for the box jacking works. Two 30m long portions of the APM and BHS tunnels were jacked as continuous precast reinforced concrete boxes under the AEL embankment within a ground improved grout block. A horizontal pipe pile canopy positioned above the tunnels was constructed using micro TBM methods to allow ground movement control and enhance face stability. The two boxes were jacked forward off a jacking slab using hydraulic jacks positioned at the rear of the boxes. An additional innovative strand jacking system was employed in combination with the canopy piles as an anti-drag system, which also supplemented the slab jacks thrust. The thrust forces on the post-tensioned prestressed jacking slab were restrained by a combination of rock friction and inclined temporary ground anchors. The two boxes were safely jacked to their final position in July 2022 without disrupting MTRC AEL operations.
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