Engineers Australia

Inferring soil water characteristics for Adelaide clay using fractal theory

Sachit A.J. Desa and Brendan T. Scott


A full scale trial pile wall was constructed as part of an initial investigation for a road underpass project in Adelaide, South Australia. The purpose of the trial was to determine if a soldier piled retaining wall could support a deep vertical excavation upon wetting up of the unsaturated clay behind the wall. Soils encountered in this case study were clays of low-to-medium plasticity, and were shown to be fractal via the use of sieve and hydrometer testing, whereby a linear relationship between particle size and percentage passing was obtained when plotted on a logarithmic scale. The confirmation of this Adelaide clay soil being fractal, and that fractal dimensions of particle size and pore size distributions are not equal, are findings that are of significance in gaining a greater understanding of unsaturated soil behaviour. Soil water characteristics inferred from fractal theory are described within this paper, in addition to the results obtained from laboratory testing for suction and moisture content of soil sampled during the trial investigation.