Construction of the Lion Rock Tunnels

September 7, 2021 Tymon Construction

Tymon Mellor: The Lion Rock Tunnels are a key part of the Hong Kong road network, linking Kowloon to the New Territories, allowing goods and people to move across the territory. However, they were not originally conceived to serve vehicular traffic but as tunnels to carry large diameter water mains from the Shatin Treatment works to new service reservoirs in Kowloon. The first tunnel was required to support the new Plover Cove water supply scheme, an integrated supply network using new northern reservoirs and water supplies from the mainland East River.

Conception

As reported by Mr Arthur Grenfell Clarke, the Financial Secretary to Legco in March 1961[i], “It is necessary under the Plover Cove Scheme for a tunnel to be driven through Lion Rock to carry three large pipes through which filtered water will flow from Sha Tin. It occurred to us that as we had to drive the tunnel in any case, it might be worth while making it big enough ultimately to take a road.”

The estimated cost for driving the tunnel was $5.5 million and there would be additional costs to fit the tunnel out for the water and road traffic. As Clark noted, “It will be some years before the road materializes, but when it does, it will provide a route to Sha Tin alternative to that now in use along Nathan Road and round Kowloon Reservoir.”

In the summer of 1958 work commenced on the Plover Cove scheme by Messrs Binnie Deacon and Gourley in collaboration with Scott and Wilson Kirkpatrick and Partners. The scheme would establish new reservoirs in the New Territories, connected by tunnels and a new reservoir in the Shing Mun valley to supply a new water treatment plant at Shatin. From the treatment works, the water would be delivered by pipelines to service reservoirs in Kowloon. An assessment was undertaken on the operational benefits of pumping the water over the Kowloon Hills or constructing a tunnel, and the latter was found to save $5 million a year in pumping costs[ii]. The capital cost of the tunnel was not considered to be significantly higher than the alternative due to the cost of the additional pumps and pipework. The final design required a single 1.4m and two 1.2m diameter steel mains.

At the March 1960 Finance Committee meeting, funding was approved to proceed with Stage 1 of the Plover Cove scheme, including the Lion Rock tunnel. The approach roads would be addressed later. Tenders for the work were issued and in June 1961 construction of the tunnel was awarded to the Societe Francaise D’Entreprises De Dragages Et De Travaus Public (Dragages) for $15 million. Dragages had an excellent record having just successfully completed Kai Tak runway and Shek Pik Dam.

Design

The tunnel was designed to be 1,424m long with a width of 9.7m and a face excavation area of 77m², and this was the largest tunnel to be constructed in Hong Kong at the time. The tunnel is a horse-shoe shape to provide the optimum arrangement for the operational requirements and the 600mm concrete lining.

The tunnel portals were strategically located to allow integration with the existing road network on the Kowloon side and in close proximity to the new treatment plant on the Shatin side. To minimise mobilisation costs, the tunnel was driven from the Kowloon side where access was easily available. To minimise the impact of water inflow during construction and operation, the Shatin portal was set 3.3m higher allowing water to drain to the Kowloon portal.

Tunnel Construction

The rock on the Kowloon end of the tunnel was heavily fractured and exploratory drilling indicated good rock would not be encountered until 122m into the drive. Tunnelling commenced in January 1962 through badly decomposed granite and competent rock was not encountered until 174m of tunnel had been excavated. Through the difficult ground, steel arches were placed at 900mm centres to secure the tunnel roof and sides.

Excavation of the tunnel was undertaken using a travelling steel drilling “jumbo” manufactured in France. The drilling jumbo, weighing nearly 32T, ran on rails and supported five compressed air drills each with a 4.3m long steel drill bit. The drill pattern required 130 holes across the face between 1.8m to 4m long depending on the quality of the rock. A daily blast consisting of around 340kg of gelatine initiated using electrically fired detonators, produced around 800-900T of rock to be removed. The blasted rock was removed with an electrically powered Landsverk L85 tunnel loading shovel served by regular diesel trucks. Problems were encountered with poor tunnel ventilation due to pollution from the diesel vehicles requiring upgrading of the system.

With a daily advance rate of 3.6m a day, the tunnel reached halfway by April 1963 after encountering a number of major faults, slowing production due to the need to construct steel arches to support the ground.

The tunnel broke through on the 20^th November, 1963 after 23 months driving when Mr E Wilmot-Morgan, the Deputy Director of the Public Works Department, set off the last blast under the direction of Mr J Payne the Public Works Department engineer in charge of the tunnelling works. Following the blast, the two vehicles carrying guests, press and engineers entered the tunnel before having to climb over the debris and walking the final 180m to the Shatin portal[iii].

The tunnelling work had created 325,000T of rock, used 150T of explosives, 380T of steel supports, 1,000 rock bolts, and 100,000T of concrete[iv].

In August 1964 work commenced on the 3.2km road connection to the Shatin portal, and by the end of 1964 work commenced on the road to the Kowloon portal.

By the summer of 1964, installation of the three water mains within the tunnel progressed allowing two of the pipelines to be brought into service, along with the rest of the Plover Cove stage 1 works on the 1^st March 1965[v]. Construction of the concrete road deck and ceiling commenced in the summer of 1965 and were completed within 24 months.

In February 1965, the Government announced that motorists using the tunnel would have to pay a toll, and that this would be set at 50 cents a car. In January 1967, a contract was awarded to Jardine Engineering Corp and Plessey (NZ) Ltd to supply toll equipment and a tunnel control system. With the completion of the ventilation system, lighting and emergency power supply, the tunnel was ready for opening. Thus, on the 14^th November 1967 with a final cost of $22 million, the Governor Sir David Trench cut a ribbon between two of the toll booths, opening the tunnel.

2^nd Lion Rock Tunnel

The High Island water scheme was to provide additional water supply, requiring the upgrading of the Shatin Treatment works and new water supply mains to Kowloon, and thus a second Lion Rock tunnel was proposed. This new infrastructure would also help address the growing concern over supporting the growing development of Shatin. As recorded by Mr Oswald Cheung in Legco 1970[vi] “It is true that, for present purposes, the Lion Rock Tunnel has spare capacity, but put another million or even half a million people into Sha Tin, and it will become obvious that development of roads and other means of communications will be a prime necessity. I am glad to see that a new tunnel might be made in connection with High Island Reservoir project, but I am inclined to think that a four or six lane highway along the present Tai Po Road would be needed”.

The tunnel would be the same design as the first tunnel but this time with two 1.5m diameter water mains. In November 1972 tenders were called and in January 1973 the work was awarded once more to Dragages for $29 million. A further $10 million was estimated for road works and $11 million for the new waterworks.

Work commenced with the preparation of the tunnel portals to the west of the existing tunnel, before tunnel excavation commenced from both ends. At the end of April, 1974 after 10.5 months of excavation the two tunnels met up when the Director of Public Works Mr David McDonald fired the final blast[vii].

Installation of the two water mains commenced allowing installation of the concrete road deck to commence in the summer of 1975 with completion within 18 months. By July 1977 installation of the $2.25 million control system once more supplied by Plessey (NZ) Ltd had commenced.

On the 18 January, 1978 the Governor Sir Murray MacLehose formally opened the tunnel before driving through the $68 million project in the company car.