4.1.1 CBL is targeted to be commissioned by 2020. Hence, the construction of CBL would start end of 2016 for completion in 2020, involving a construction duration of 4 years.
4.1.2 The CBL project is composed of an approximately 1.8km long dual-lane carriage way mainly on viaduct, an outwardly leaning arch bridge, approach structures, an adjacent road (Road D9) and a cycle ramp. The proposed methodology for the construction of these is described below.
4.2 Construction Methodology for Cross Bay Link
4.2.1 The major construction works would comprise the following activities:
· Foundations – installation of piles by marine piling rigs, erection of cofferdam, building of pile caps and building of piers;
· Substructure and superstructure – erection of concrete deck segments of the approach and installation of main bridge and side spans; and
· Construction of the cycle track ramp.
4.2.2 No dredging works are envisaged for the construction of CBL.
Foundations
4.2.3
Piling and pile cap
construction would occur in three different sections for the Main Bridge,
Eastern Approach and
Western Approach.
4.2.4 Marine drilling rigs would be used for the installation of piles. One drilling rig to be used for the Eastern Approach foundations and one drilling rig to be used for the Western Approach as well as the Main Bridge foundations. There would be two marine piling fronts in total and the works undertaken in the following sequence.
4.2.5 A silt curtain would be placed around each foundation construction location to form the first line of defence against dispersion of sediment plume during pile, pile cap and pier construction. Steel sheet piling would be undertaken within the silt curtain to form a cofferdam and a second line of defence against dispersion of sediment plume during excavation of piles and construction of the pile cap.
4.2.6 Cylindrical steel casings (of the pile diameter) would be installed at each pile location within the steel sheet pile cofferdam. Excavation from within the cylindrical steel casing would be undertaken from the seabed level down to the pile founding level. The excavated materials would be transported from cylindrical steel casing by watertight closed-grab to a construction barge.
4.2.7 Following the excavation stage, a steel reinforcement cage would be lowered to the excavated void within the cylindrical steel casing. Concrete would then be poured by skipper to fill up the excavated void. The cylindrical steel casing would then be slowly retrieved by vertical pull during the concreting work.
4.2.8 For construction of the pile cap, temporary false work and formwork would be erected within the steel sheet pile cofferdam, the reinforcement placed into position and concrete would be placed to complete the pile cap.
4.2.9 This construction method would avoid the need to dredge sediment because the pile cap would be located above the sea bed. Sediment excavated from within the cylindrical steel pile casings would be placed in a barge and disposed in accordance with regulations.
4.2.10 Derrick barges would be used to transport steel pile casings to foundation locations and a crane would lift and place them into position. The pile casing would be installed using a hammer rig and the concrete would be supplied by another barge containing the concrete lorry mixer.
Substructure
4.2.11 Barges with cranes would be used to transport the formwork and materials to the pier locations. The cofferdam used for piling would remain in place while the piers would be cast in-situ.
4.2.12 After completion of the substructure, the steel sheet piles of the cofferdam would be retrieved from within the silt curtain by slow vertical pull. The silt curtain would then be removed.
Approach superstructure
4.2.13 The concrete deck segments for the Eastern and Western Approach of the bridge are proposed to be fabricated in Mainland China.
4.2.14 The deck segments would then be transported from the fabrication yard to site by barge. Segment erection would be carried out by floating cranes using balanced cantilever method. Adjacent segments would be connected using in-situ stitching method after completion of the segment erection. For the Eastern Approach, when the depth of water would be too shallow for a floating crane to operate, lifting frames would be used.
Main bridge superstructure
4.2.15 A total of eight steel deck segments of 50m length and two arch segments of 220m (440m in total) have been proposed and would be fabricated off-site in Mainland China.
4.2.16 The arch and main span deck segments, as well as the side span segments, would be brought to an assembly site in Mainland China and assembled before delivery to site in Hong Kong.
4.2.17 Cranes would be used to lift the main bridge onto a large barge at the site before being floated into position. Strand jacks attached to four corners of the bridge would lift and position the main bridge. In-situ welding would be carried out to realize the complete structure.
Cycle Track Ramp
4.2.18 The foundations of the cycle track ramp would be built on land to a suitable depth. The cycle track ramping from the ground level (~5m) up to the deck level (~10m) of Road D9 would be built on columns of varying heights.
4.3 Construction Methodology for Road D9
4.3.1 Earthworks for the modification of the seawall would include excavation and backfilling of general fill material, quarry spall and rubble. In order to avoid excessive water pressure on the existing seawall during excavation, sheet piles would be installed and the water would be pumped out prior to the earthworks.
4.3.2 Other major construction activities would include sea wall strengthening where the existing sea wall would be extended and strengthened, ground improvement works by means of compaction grouting, piling for noise barrier using pre-bored H-piles and noise barrier erection works.
4.4.1
The tentative construction
programme of CBL is provided in Appendix
4.1
4.5.1 The envisaged construction plant inventory is provided in Appendix 6.3.