December_1967 — Page 35

HONG KONG

T. R. B

ARCHITECTURE

DEPARTMENT

THE

пун

LION ROCK TUNNEL

OPENED TO TRAFFIC

HE 4,677 ft. long tunnel driven through the granite of Lion Rock was opened to traffic last month. It has taken two years and four months to complete, at а total cost of HK$22.17 million.

First conceived in 1960 as an economical route for conveying water from the Sha Tin filters of the Plover Cove water supply scheme to the urban areas of Kowloon, the project was later expanded to a dual-purpose scheme providing both a water supply link and an additional road link be- tween Kowloon and Sha Tin, New Territories.

The contract for driving the tun- nel, to an average diameter before lining of 34 ft., was awarded in May 1961. This work was completed in September 1964 and was followed by the laying of the water mains, con- struction of the roadway and the in- stallation of the ventilation, lighting and toll equipment. Some 325,000 tons of rock was excavated from the

tunnel and 150 tons of explosives were used in the driving.

Generally the rock encountered was of sound granite but the first 900 ft. from the Kowloon portal was in various stages of decomposition and had to have structural support. Some areas of weakness due to the intru- sion of diorite dykes were also experi- enced.

There are three water mains two of 48in. diameter and one of 54 in. These, together with an air inlet duct, are laid beneath the road. They carry at present about 80 million gal lons per day but are capable of carry- ing twice that amount.

Dimensions

The principal dimensions of the tunnel are as follows:

Length, portal to portal

4,677 ft. (1,425 m.) Finished cross-section

746 sq. ft. (69 sq. m.)

blad

Maximum clear width

28 ft. (8.5 m) Carriageway width

23 ft. (7 m)

Minimum headroom for vehicles

15 ft. 6 in. (4.7 m) Longitudinal gradient

1 in 400 from Sha Tin Portal Width of service walkways

18 in. each (0.46 m) Road construction inside the tun- nel commenced in July 1965. The reinforced concrete road slab and the two supporting walls underneath have been designed to full Ministry of Transport loading. With a minimum headroom of 15 ft. 6 in., the road is capable of taking double-deck buses and other heavy commercial vehicles.

The ceiling consists of 3 in. thick precast reinforced concrete units which are supported by precast con- crete beams secured to hanger bolts which are in turn screwed into rock bolts in the tunnel roof. The hollow compartment above the ceiling serves

Drilling

Far East Architect & Builder December, 1967

H.K. Govt. Photo

Steel arching

H.K. Govt. Photo

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