Pitching piles prior to driving
After removal of the serious ob- structions, the piles, which have a design load of 45 tons, were to be driven to withstand satisfactorily a test load of 90 tons, the main criterion for acceptance being that the pile would be required to carry the test load for a period of not less than 72 hours and that during the last 48 hours of the test there should be no appreciable settlement. In addition the nett settlement after removal of the entire load should not exceed 4 in. On the basis of applying the test requirements to the Hiley Formula it was decided to drive the piles to a set of not less than 35 blows per foot with the 5 ton hammer falling through 36 in.
Most of the piles were able to achieve such a set within 60-70 ft. but those piles which drew up at a substantially lesser depth compared to those of their neighbours in a par- ticular group were test loaded. Dur- ing driving, a few of the piles were broken by unknown obstructions and these were replaced by the contractor.
One of the piles was driven to its full length of 79 ft. 9 in. with a set of only 24 blows/ft. penetration in- dicating a Hiley carrying capacity of only 76 tons but this was subsequent- ly proved to be satisfactory under the test load of 90 tons.
Although generally obstructions caused by the old Naval Dockyard were a nuisance, the flyover was able to make good use of the old dry dock which had been filled in and lay beneath the surface of Harcourt Road. The foundation of pier 2 was provided by comparatively short piles fitted with rockshoes and driven to the bottom of the dry dock. The foundations for piers 1 and 3 were provided by simple reinforced con- crete pads resting on the dock walls.
The dry dock was not in exactly the location indicated on the old re- cords and the positions and angles. of the piers had to be slightly adjust- ed so that the foundations sat truly on the line of the dock. The adjust-
Far East Architect & Builder June, 1966
ment was only small and did not necessitate major redesign of the bridge deck above. An old staircase was discovered in the thickness of the wall beneath pier 1 (which led down to the galleries at various levels run- ning the length of the dock). was pumped and cleared out, sand- bagged and filled with 20:1 concrete so as to form a level base for the foundation.
Pilecaps
This
Excavation for the pilecaps was started as soon as the driving of each group of piles was completed. The piles were stripped to expose the re- inforcement, the bottom of the ex- cavation was sealed with concrete and steelfixing and concreting up to bottom of pier level followed in the usual way. At the same time as pouring the pilecap, the first 3 in. of the piers was cast so as to provide a starter for the work which was to follow.
Deck spans under construction
The first foundation up to starter level (abutment A) was completed by mid February and the last, (pier 8) by mid July. Due to the various obstructions progress was haphazard and limited up to this period and as piles could only be driven where there were no obstructions it was not possible to drive in a logical sequence.
However, in February 1965, by which time four of the foundations were completed, the whole contract was reviewed in some detail and a reasonable forecast was made of the dates by which the remaining foun- dations would be finished. As a result of this investigation the work was planned so that the structure could be completed at the earliest possible date. The sequence decided on was that alternate spans would be cast starting from each abutment and working towards the centre and the spaces would be filled in the same directions when once the first series was completed.
This method had the advantages of the minimum transporting distance of formwork for each usage, an early opportunity to fill the ramps which would require time to consolidate. and finally that there would be no delay in forming the roads turning under the flyover. As a result of this planning the forecasted finishing dates of the foundations had to be re-as- sessed and the contractor had to make concentrated efforts to meet certain critical completion dates for some of the foundations while on others it was found there would be time to spare.
Piers and Abutments
The contractor decided to use timber formwork for the piers and was encouraged to use 1 in. plywood for linings above ground. Although the basic cost of plywood linings was about 40 per cent. more than loose boards, savings would be made be- cause of the absence of planing, was-
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