The first tunnel linking Hong Kong's Island with Kowloon took 20 years between conception and formal opening. It was a substantial challenge in terms of design, construction and supervision, being the first submerged tube tunnel to be planned and built by an all British team of consultant and contractor. The tunnel was also a very early, and successful, example of privately financed infrastructure.
This was in the early 1950s when the only way to get to Hong Kong from the mainland was by ferry. A group of British businessmen realised this was a serious barrier to the development of the territory and appointed the firm I worked for, Scott Wilson Kirkpatrick & Partners - now Scott Wilson. I worked as consultant for the construction of a fixed link crossing.
A tunnelled crossing gained favour. The senior partner to whom I reported, Geoffrey Williams, suggested an immersed tube; and I with others set about determining feasibility.
There were few examples around the world to study, and much of our work involved original research. For instance, how deep should the trench backfill be to protect the immersed tube in the event of a ship dragging its anchor during a typhoon?
Eventually the firm was satisfied that a submerged tube was the right solution and a proposal was made. Later a franchise was granted to the privately owned Hong Kong Cross-Harbour Tunnel Company to build and operate a tunnel with ownership reverting to government after a fixed period.
Tenders were invited based on a concrete tunnel scheme, but British contractor Costain won with an alternative twin steel tube solution.
Total length of the tunnel from portal to portal was 1.85km with a submerged tube tunnel of 1.6km being formed of 15 units each about 107m long. The steel tubes had a 10.4m diameter, each carrying a 6.7m carriageway of two lanes of traffic. The tunnel was constructed in a maximum water depth of 30m, and was completed on time and within budget. It was officially opened by Princess Alexandra in 1972.