Foundations Post-Second World War

The Narrows Bridge, in Perth, incorporated 'Gambia piles' (so named because an early form of them were used in the Gambia), consisting of 31 inch diameter reinforced concrete cast inside a permanent steel casing. The casings incorporated 15 ft long reinforced concrete toe sections and were driven with a maximum length of 150 ft by means of a 12 ton drop hammer acting inside the casing.

In 1962, John Holland Constructions incorporated slender composite piles in their alternative design for the Captain Cook Bridge, Sydney, based on the research of Professor Francis and others at the University of Melbourne. With an overall length of 220 ft, they consisted of 20 inch square pre-stressed concrete upper sections joined to 14 x 14 1/2 inch steel H piles. These were, at the time, claimed to be the longest driven piles in the world; they may well remain the most slender. Soon after, construction of the Tasman Bridge at Hobart designed by Maunsell and Partners, utilised 52 inch diameter grouted 'Colcrete' piles cast inside steel casings, sunk by oscillation and grabbing to a maximum depth of 260 ft. Tests on some of these piles showed excessive deflection under load; this was remedied by a novel procedure of cyclic pre-loading developed by Dr. D. H. Trollope.

Westgate Bridge, in Melbourne, incorporated 5 ft diameter cylinders, sunk to a depth of 200 ft by oscillation and internal excavation, to which record test-loads (1500 tons of concrete kentledge blocks) were applied (Fig. 24).

24 Westgate Bridge Nov. 1968 -East minor spans, piling and test load (By courtesy of Westgate Bridge Authority)

Finally, a few years later in 1970, interest returned to the Hawkesbury River, where a world record was again challenged with driven hollow composite piles up to 283 ft long installed for a new expressway bridge.

Outstanding examples of deep ground compaction techniques, now part of the standard repertoire of foundation engineering, are provided by two major projects constructed in Western Australia in the early 1970s. Construction of a major freeway interchange and city car park in Perth involved the reclamation of some 90 acres from a stagnant reach of the Swan River. Underlain by some 40 to 100 ft of very soft organic silty clay, a complex system of vertical sand drains and surcharge loads speeded the consolidation of this layer (up to 23 ft of settlement was measured) to permit embankment construction within a reasonable construction period. To eliminate lateral and drag down forces on the piled foundations for the interchange structures, the 4 ft diameter pile cylinders were isolated from the surrounding material by 7 ft diameter steel caissons. The C.B.H. Grain Terminal at Kwinana was founded on Frankipiles installed over a 10 hectare site in a deep sand stratum which had been previously compacted to a depth of 80 feet by Vibrocompaction, a technique involving the use of vibrating probes (Fig. 25).

25 Pile Driving at Kwinana (By Courtesy of Frankipile)

Australian Academy of Technological Sciences and Engineering