Underwater tunnels of the Hong Kong MTR

In Hong Kong there are four railway tunnels carrying trains under Victoria Habour between Hong Kong Island and Kowloon. Here is a summary of how each was constructed.

Southbound train emerges from the tunnel at Kwai Hing station

MTR Harbour Crossing Tunnel

Location: Admiralty to Tsim Sha Tsui
Railway: Tsuen Wan Line, between Tsim Sha Tsui and Admiralty stations
Carries: 2x railway tracks in separate tubes
Commenced: 1976
Completed: December 1979
Type: Immersed tube, reinforced concrete double binocular section
Length: 1400 metres
Width: 13.1 metres
Height: 6.5 metres
Depth: 24.24 metres

The tunnel is made up of 14 immersed tube units, each 100 metres long and weighing 7,800 tonnes. The tunnel was built on a 2800 metre radius curve due to the railway running north-south in Kowloon and east-west on Hong Kong Island.

Each binocular section was constructed of concrete reinforced with longitudinal prestressing, in a casting basin at Chai Wan on north-east Hong Kong Island. The units were placed on a screeded gravel mattress foundation, with the final closure joint between unit No. 12 and No. 13 achieved underwater using tremie concrete.

Eastern Harbour Crossing

Location: Quarry Bay to Cha Kwo Ling
Railway: Tseung Kwan O Line, between Yau Tong and Quarry Bay stations
Carries: 2x railway tracks, 2x dual road lanes, ventilation duct
Commenced: August 1986
Completed: September 1989
Type: Immersed tube, reinforced concrete box
Length: 1860 metres
Width: 35.45 metres
Height: 9.75 metres
Depth: 27 metres

The Eastern Harbour Crossing carries both road and rail traffic across Victoria Harbour, in five separate immersed tubes.

Each of the 15 precast reinforced concrete units are 128 metres long, and at 35.45 metres were the widest concrete tunnel sections built in the world up until that time. They were cast in three batches of five at a 5.5 hectare dry dock at Cha Kwo Ling, on the northern shore of the tunnel.

Western Immersed Tube

Location: Central to West Kowloon
Railway: Airport Express and Tung Chung Lines, between Hong Kong and Kowloon stations
Carries: 2x railway tracks
Commenced: late 1994
Completed: December 1996
Type: Immersed tube, reinforced concrete box
Length: 1260 metres
Width: 12.4 metres
Height: 7.7 metres
Depth: 28 metres

Options for combining the tunnel with the Western Harbour Crossing vehicular tunnel were considered at feasibility stage of both projects, but the alignment constraints resulted in two separate tunnels being constructed.

The ten tunnel units are of twin-cell prestressed concrete construction, each being 126 metres long. They were fabricated in three batches of 4, 2 and 4 units respectively, in the Shek O casting basin.

Due to the railway running north-south on the Kowloon side and east-west on Hong Kong Island, the alignment follows a 60° curve: tunnel units are a mix of straight, transition curves, and minimum 850 metre radius. At the Hong Kong landfall is a special tapered unit, to accommodate the turnouts towards the separate Airport Express and Tung Chung Line platforms at Hong Kong station.

Shatin to Central Link Cross Harbour Tunnels

Location: Admiralty to Hung Hom
Railway: North South Corridor, between Exhibition and Hung Hom stations
Carries: 2x railway tracks
Commenced: mid 2015
Completed: 2021 (expected)
Type: Immersed tube, reinforced concrete box
Length: 1700 metres
Width: ?
Height: ?
Depth: ?

The eleven pre-cast concrete tunnel units are being cast at the former Shek O Quarry, and are each approximately 160-metre long and 23,000 tonnes in weight.

Sources

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