10-0
33-0"
92'-0"
Services
Fig. 3. Typical section-marine span
1601
33'0"
Surfacing
For the result of the test to be considered satisfactory, a pile had to carry the test load without settling more than in. during the 24-hour period following application of the full load.
Under the terms of the contract, the contractor was required to deter mine the lengths of piles from the results of one test pile at each grid and any other investigations that he considered necessary. In the event, he proposed that probing be used to supplement the information obtained from test piles.
It was considered that piles could be driven to depths where the standard penetration (n) values were around 150. This proved to be generally the case and, in the event, only few piles required extending or cutting.
Pile manufacture
Pile casting was carried out on the site on specially prepared concrete beds using bolted steel side shutters.
Generally, lifting and handling of land piles up to 70ft. in length was done by the standard two-point system but, for longer piles, it was decided to adopt a four-point system. Rail bogies were used to transport piles on the site.
There were a few instances where exceptionally long land piles, up to 135ft. in length, were required. In order to ensure safe and practicable handling, however, no pile longer than 90ft. was cast. The additional length was obtained by extending the pile after initial driving, followed by re- driving to final set.
Prestressed piles for marine use
5-3%
Service
4-0"
were cast on 300ft. long beds. For ease of movement when detensioning, a polythene membrane was placed on the bed before pouring concrete.
A 6-ton hand operated hydraulic jack was used for pretensioning the high-tensile wires, which were stressed in a set sequence to ensure even stress distribution on the anchor block. Lengths of marine piles varied from a minimum of 20ft. at the west side of the bay to a maximum of 90ft. at the pier nearest to the sea wall.
Pile driving
On land, standard rigs were used for pile pitching while driving was done with drop hammers. A 4.8-ton
hammer was used for 16in. square piles
up to 60ft. in length, the weight being increased to 6.0 tons for longer ones. Irrespective of their length, 18in. square piles were driven with a 7.5 ton hammer.
Handling, pitching and driving of marine piles was all done from a float- ing pontoon equipped with a 20-ton derrick crane at one end and a special lattice steel tower at the other. The tower was designed to cantilever out from the pontoon to provide a means of driving raking piles in any direction simply by changing the position of the leaders within the tower. A single- acting steam hammer weighing 8.0 tons was used throughout for driving piles to sets similar to those adopted for piling on land.
Marine pile caps
The soffit level of the marine pile caps was fixed at +4.00ft. P.D. allowing them to be cast during the monthly spring tides. The top level of the caps was +9.00ft. P.D. making them visible during high tides.
One of the contractor's problem was how to design a shutter to take the dead weight of concrete and be capable of withstanding the upward forces of floatation before concrete was placed.
A satisfactory system was devised whereby timber bearers and soffit boards were held firmly and supported by steel joists bolted to 11⁄2in. diameter steel bars hanging from a steel grillage system which was propped by steel joists off the piles. The props were welded to the pile reinforcement and cast into the pile caps. End forms
were left out until the last moment to
Lifting beam to deck level prior to moving on bogies for sea span
Far East BUILDER, April 1969
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