May_1966 — Page 65

made.

the second scheme was adopted. In view of the very com- plicated sub-structure work and the time required to produce the design drawings, etc., for the superstructure. separate tenders were invited for the two stages of the work, thus enabling the detailed design of stage II to proceed while stage I was underway.

The shape and form of the columns and cantilever beams were identical for each pier except for the variation in height, thus enabling considerable repetition of formwork. A column width of 4 ft. at the base with slopes on the column and beams of 1:9 was adopted, producing a simple, slender shape.

As prestressing work in the Colony is still very much in its infancy it was decided to keep the design of the beams as simple as possible by as- suming simply supported beams and adopting a constant cross section for all beams irrespective of length; this also enabled constant repetition of formwork and the reduction in cost of shuttering more than compensated for the additional concrete used.

The superelevation and cross fall of the roadway was incorporated in the concrete road slab SO that it varied in thickness between 7 in. and 19 in. Expansion joints were pro- vided at each pier.

Construction

Stage I Substructure

Tenders for construction of the piled foundations were called for in August 1964 and the tender of Paul Lee Engineering Co., Ltd. was ac- cepted in September 1964. Work commenced in October, 1964.

Steel shuttering for prestressed beams cast at the contractor's yard at Hung Hom

Pier No. 17 under construction in June, 1965

tractor to supply pile group at each pier capable of carrying the design load, but permitted him to design his own pile and pile grouping. Each group was paid as a lump sum but the excavation, pile caps, etc.. were all measured separately.

The contractor carried out his own standard penetration tests at each pile group prior to driving, confirming the results produced previously.

The whole pile cap area was ex- cavated to expose all the utilities prior to driving and only very minor changes were necessary to enable the piles to be driven.

The contractor had his own supply of precast piles so that after calculat- ing the length of pile required, the 14 in. x 14 in. precast concrete piles were brought straight to the site on low-loaders and were lifted and pitched direct, with the usual tackles and blocks, by the 80 ft, steel piling frame.

Piles were driven using a 7-ton drop hammer with a drop varying from 6 in. up to a maximum of 3 ft. Owing to the extremely tight site conditions available it was impossible to use the normal guy-ropes so the piling frame was weighed down using 5-ton and 7-ton hammers on the

corners.

The piles had to be driven very carefully between the existing utili- ties. The tolerance in setting and pitching was very small, being kept down to about 1⁄2 in. in any direction.

A total of 256 piles were driven in the course of the contract, without a single damaged pile. This can be attributed to the use of the heavy hammer and the excellent workman- ship of the contractor. Test loads The contract called for the con- were made on two piles selected

Far East Architect & Builder May, 1966

arbitrarily. These were required to carry a test load equal to twice the working load for a period of 48 hours with a nett settlement not exceeding 0.25 in. The maximum nett settlement recorded was 0.045 in.

Pile caps were designed after the pile groups were driven and ac- curately surveyed. The piles were stripped to expose the pile reinforce- ment and construction of the pile cap proceeded in the usual way except that ready-mixed concrete was sup- plied by a specialist supplier. This enabled work to proceed at a very fast rate and the first stage was com- pleted in January 1965 at a total cost of HK$428,066.

Stage II Flyover and Road Works

Tenders for the flyover superstruc- ture and the ancillary roadworks were called for in December. 1964 and the tender of Paul Lee Engineer-

VA

End view of Lee-Macall bars and bearing plates

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