August_1970 — Page 43

ft. high) were constructed by cut-and- cover method and waterproofing was effected by means of in. thick mastic asphalt. The walls of the sub- ways are finished with in. mosaic tiles and lighting consists of twin 48 in. 40 watt fluorescent lights at 10 to 12 ft.

centres.

The contract for Chatham Road flyover was awarded to Paul Y Con- struction Co. Ltd. in April 1968 and the work was completed in October 1969. The cost of the project was about HK$3,300,000.

Road connections (Mainland)

The main tunnel route starts north of the tunnel toll plaza and provides dual four-lane carriageways separated by a 4 ft. central divide. Available space is limited by the railway boun- dary on the east and the technical college compound on the west and, since the road has to pass over Chat- ham Road, it is being constructed on retained fill. Slip roads on embank- ments join to Chatham Road and the road continues as an elevated structure over Chatham Road where another pair of slip roads on earth fill are situated.

Two viaducts, each about 950 ft. long, complete the route by merging with Princess Margaret Road where, in order to provide grade separation, the existing level of the southbound car- riageway has to be reduced by 25 ft.

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(Fig. 3). requiring some 30,000 cu. yd. of excavation in hard material the task is made particularly difficult by the presence of the existing railway tracks at the foot of the steep slope.

One of the planning requirements during the construction period is the need to maintain the existing capacity of Chatham Road North which serves the airport and East Kowloon. It is also necessary in the completed scheme to provide a bridge along the road over the proposed new railway tracks from Hung Hom terminal. In order to achieve these requirements Chatham Road is being reconstructed on an alignment north of the existing road and parallel to it.

This phase of the work must be completed in the first instance before the existing road is abandoned. The new road is designed for a speed of 40 m.ph. and has a maximum gradient of 4.5 per cent. Elsewhere, the maximum up - slopes are limited to 5 per per cent and the down gradients to 7 per cent.

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Soil conditions vary considerably across the site

rock being present at Princess Margaret Road and in areas adjacent to the existing hills, de-

composed granite of varying density north of Chatham Road and reclaimed land south of it. Consequently, foun- dations to the structures are either on spread footings or on piles. Where sizes of spread footings are limited by the existing railway tracks they are secur- ed to rock using rock anchors. Precast concrete piles 18 in. x 18 in. of 100 tons capacity, are used in piled foun- dations.

Decks of the elevated structures are of a conventional beam and slab type employing precast post-tensioned box and I-beams which are standardised at 75 ft. length. Altogether, 54 box beams each weighing approximately 36 tons and 80 I-beams of 27 tons are needed.

The beams are stressed employing P.S.C.'s 7/0.5 in. monostrand system of prestressing. They are recessed at the ends and rest on inverted "T” capping beams. Each span of the 24 ft.

ICESS MARGARET ROAD (SOUTHBOUND)

PRINCESS

MARGARET

ROAD (NORTHBOUND)

Precast box beam

Precast I beam 6* In-situ concrete slab

Existing Canton Kowloon Railway

'5 MERGING WITH PRINCESS MARGARET

ROAD

Far East BUILDER, August 1970

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