Development Between First and Second World Wars

In one of the few major projects of the time, M. R. Hornibrook devised an unusual method for construction of the river piers for the Grey Street Bridge, Brisbane in 1928. This involved the establishment of 'artificial islands' which permitted installation of concrete cylinders and caissons by simple dry land methods in preference to launching and floating them to site. Completion to 107 feet below high water involved open dredging down to rock, and final trimming of the foundation under compressed air.

Meanwhile, among a variety of methods being used to found the Spencer Street Bridge in Melbourne, concrete cylinder foundations were constructed within some remarkable circular prefabricated timber cofferdams 9 ft 6 in diameter and 37 ft deep. These were lowered through 7 ft of soft silt overlying a basalt flow, excavated and de-watered. Despite the use of small explosive charges for final trimming of the rock they remained watertight, some remaining serviceable for four uses.

For many years architects and engineers tried to overcome the effects of the highly unstable black soils found over wide areas, particularly in Queensland and New South Wales. These suffer from dimensional changes up to 20 per cent as a result of seasonal variation in moisture content, causing extensive cracking in brickwork and finishes. In 1937 A. S. Macdonald described the foundation design for the Bank of NSW at Moree, where an inspection shaft had shown numerous cracks 12 ft deep and 3.3/4 inch wide in the plastic clay. Spread footings were constructed at a depth of 18 ft, and flexible columns raised from these, with loose concrete shells providing the necessary clearances to isolate the building from the effects of soil movement.

Australian Academy of Technological Sciences and Engineering