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The Thornthwaite Moisture Index and seasonal soil movement in Adelaide
In regions with highly expansive clay soil profiles, climate is a critical determinant of the behaviour and magnitude of seasonal surface soil heave. In this paper, the correlation between soil heave and soil moisture availability, as determined using the C.W. Thornthwaite method of estimating potential evapotranspiration, is investigated for two exposed vegetated sites near Adelaide. The study sites were characterised by highly reactive soil profiles, and were influenced by extremely variable moisture conditions due to the semi-arid climate of the Adelaide region. The effects of vegetation on soil moisture availability are demonstrated, with soil shrinkage observed to occur quite rapidly during the late spring when moisture uptake by maturing annual grasses is high. Maintaining vegetation ground cover as mulch was shown to reduce noticeably soil shrinkage during the dry summer months, thus limiting the seasonal variation in soil volume. The study results also provided good experimental justification for assuming a soil moisture capacity of 100 mm of rainfall, as recommended by Thornthwaite. Climate change predictions for Adelaide have been used to estimate future trends in soil moisture availability and Thornthwaite Moisture Index, and indicate that Adelaide’s climate will become increasingly arid. This may have significant implications with respect to footing design requirements in regions characterised by highly expansive soils.
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Annual General Meeting (AGM) and Ground Anchors and Piling Innovations
Ancorloc & Piling Contractors
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Key learnings from conducting In Situ Testing
Professor Paul Mayne, Georgia Institute of Technology
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Challenges and solutions towards natural prefabricated vertical drains
In recent years, natural fibres such as jute and coir are emerging as a reasonable alternative to synthetic materials because they do not only have favourable engineering characteristics but also degrade biologically over time. Of promising applications of those environmentally friendly materials, natural prefabricated vertical drains (NPVDs) have received considerable attention, however their application is still limited. This paper summarises existing issues which are hampering these novel drains from a wider application, followed by studies carried out by the authors to overcome those limitations. Particularly this includes: (1) hydraulic properties of NPVDs considering macro and micro features; (2) modelling NPVDS including analytical method and a novel numerical approach to capture micro-hydraulic behavior of fibre drains considering fluid-fibre interaction; (3) bioderadable characteristics of NPVDs exposed to saturated soft soils; (4) analytical and numerical solutions to incorporate biodegradation of NPVDs into consolidation of soil.
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An investigation into opportunities for improvement of surface mine haul road functional design, construction and maintenance
Mine haul roads are a key component of a mining operation. However, design of haul road pavements often follows an approach that is heavily reliant on site experience. This approach does not allow an assessment of the production impact of different design options. This paper compares the estimated haul truck energy consumption for a range of pavement wearing course materials including mine waste (overburden), select gravels, mechanically stabilised mine waste and cementitiously modified mine waste. Haul truck energy consumption was estimated from rolling resistance, which was determined from the pavement roughness. Modelling of pavement roughness included material, traffic and maintenance inputs. Samples of each material type were collected from an iron ore mine in the Pilbara region of Western Australia. The analysis shows that the energy consumption correlates best with the fines content and activity, represented by the Shrinkage Product, of unbound wearing course materials. As a result lower truck energy consumption appears possible with the use of select gravels, mechanical stabilisation and cementitious modification.
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Western Australian Pavements in Colonial Times 1829 to 1860
Western Australia’s early settlers used boats for river and sea transport or travelled along roughly cleared streets in the town sites and on rugged narrow tracks between them. As the colony extended inland the initial streets and tracks became inadequate. Also the need for organisations to take responsibility for the construction and maintenance of good roads soon became apparent.
The early organisations lacked the practical knowledge to select suitable pavement materials. The clay, probably silty clay from the river, favoured by them for use on the streets of Perth soon became a problem during the winter rains. While information on construction methods is not available there is no evidence that compaction was considered. However tender documents in the 1850s suggest the realisation of the benefits of granular material in the pavements. On the coastal plain such material was quarried from limestone outcrops, in the inland areas the use of laterite gravel gradually became accepted. Early settlers, dissatisfied by the poor performance of the roads, soon made their feelings and needs known. The arrival of the Royal Engineers in the 1850s introduced civil engineering expertise to the significant benefit of the colony.
Material for this paper was gathered from contemporary reports and to a large extent from newspaper articles and editorials written by journalists. Nevertheless, they provide some clues as to the decisions about the availability and suitability of pavement materials in the early times of Western Australia (WA).