Mechanisms affecting high subsoil strength in the soils of a reconstructed landscape

[Truncated abstract] On the coastal plain of south-west Western Australia mineral sands are mined from ancient strandlines buried several metres below the current ground level. The mining of these strandlines involves considerable soil disturbance which physically degrade the native soil. The successful rehabilitation of a site reconstructed less than two years prior to this study was limited by structureless subsoils with high soil strength. The increase in soil strength (determined by penetrometer resistance) was a result of the breakdown of soil aggregates due to disturbance, and the contribution of wetting and drying to the collapse of the newly constructed soils. The impact of severe disturbance on the soil materials used for soil construction is not well understood, however, effective measures of the impact of disturbance and rehabilitation processes can be identified by a comparison of native and constructed soils. The objectives of this study were i) to examine the relationship between soil strength and the physical properties of the native and constructed subsoils and ii) to determine the effects of sand and organic amendments on the strength of newly constructed subsoils. The overall theme being to determine the susceptibility of native soil materials to soil structure decline as a result of soil disturbance, and to develop alternative soil handling techniques to support sustainable long term soil function. A field experiment was designed to measure and compare the properties of the constructed soils on a recently rehabilitated land area. Seventeen treatment plots were constructed consisting of various combinations of native soil, tailings sand, and organic materials. Immediately after soil placement a trench was excavated across the field experiment.