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Cement stabilisation of road base course: A chronological development in Western Australia
The use of cement stabilisation technologies was first pioneered in Australia as early as the 1950s. However, its use did not spread to Western Australia until the 1970s when an investigation was commissioned by Main Roads Western Australia (MRWA) to assess an alternative for bitumen stabilisation of base course. Cement stabilisation was identified to be a potential option as strength parameters of cement stabilised pavements were comparable to those of bitumen stabilised pavements. This paper presents the development of cement stabilisation technology from the laboratory investigation in 1970s, through to the construction of Leach Highway Trial Pavements, followed by the extensive laboratory testing by MRWA, and finally to the construction of Reid Highway Trial Pavements. In these investigations, cement has been assessed for its use as a stabilisation agent and subsequently a modifying agent and was found to be problematic, i.e. cement stabilised pavements exhibited issues of binder permanency, fatigue and shrinkage. As an immediate reaction to the observations of these investigations, MRWA prohibits the use of any appreciation in pavement strength from cement treatment when designing pavement thicknesses as covered in the current Engineering Road Note 9 (ERN9) 2010. A review of these events leading up to the publication of ERN9 2010 is presented along with testing regimes identified to close the knowledge gap.
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In situ Stress Testing for Tunnel Design in Sydney – Hydraulic Fracturing and Overcoring
Over the last decade there have been several road and rail tunnels designed within the Sydney Metropolitan area that are now well into construction. For these tunnelling projects, a key design input has been an estimate of the magnitude and orientation of the in situ stress. Designers typically consider the measurement of in situ stress from boreholes located along the project alignment and also from published stress measurements and empirically derived relationships for the Sydney Basin. This is because there is often significant variability in the results obtained from limited stress measurements for a given project and a reasonable interpretation of these results needs to take into account a number of factors such as geological and topographical situation. Measurement technique is also a source of variation and practitioners need to be aware of the limitations and advantages of these to ensure that a stress measurement program has the opportunity to deliver the required project needs. This paper considers in situ measurements made within boreholes in Sydney using the commonly-used hydraulic fracturing method and the more recently used overcoring method by the Sigra IST tool. Results from two infrastructure projects, where these two methods were used, are presented and the possible reasons for differences obtained between the two methods are discussed. The process of overcoring is a focus including the factors that influence the determination of the elastic properties of the rock for the calculation of the in situ major horizontal stress. Numerical modelling is used to examine the potential for brittle microcracking in the porous Sydney sandstones, which can damage an overcored sample and invalidate elastic parameters obtained.
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Quantitative Risk Assessment Of The Thredbo Landslide
A quantitative assessment of the risks associated with landslides from the Alpine Way was completed in 1998 as part of the advice provided on behalf of the NSW Coroner. The objectives of this risk assessment were to provide a basis for understanding the Thredbo Landslide and to compare the estimated risks with those generally accepted or understood in society. The assessment reported here considered the situation at the time of the landslide; considerable works have been completed since the landslide and it is considered that this assessment would no longer apply.
The assessment focused on the Alpine Way and did not include assessment of the natural slopes well away from the road because:
- the natural slopes along the Thredbo Valley showed no evidence of significant mobility of natural slides in the recent past, and
- over the last 43 years the only known mobile landslides in the area of interest had been associated with the Alpine Way. It is possible that mobile landslides from above the Alpine Way could occur in the future but these have not been considered further in this paper.
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Hencky’s remarkable equation
Hencky’s Equation, used extensively in the theory of plasticity, is shown to provide the basis for the solution of many routine geotechnical problems, such as the bearing capacity of footings, the lateral resistance of piles and surcharge pressures on retaining walls. The original Hencky’s Equation applicable for weightless φ = 0 soils is extended to general c,φ soils, and is shown to accurately predict the results of hollow cylinder tests. The extended Hencky’s Equation enables the derivation of the bearing capacity of strip footings and piles in weightless c,φ soils. A case example is given showing that justification of high pile base bearing capacities in very stiff to hard clay was assisted by using derivations from Hencky’s Equation. The life of Hencky is summarised and it is shown that despite experiencing a degree of hardship, Hencky’s contribution was remarkable and provides an inspiration to present day geotechnical engineers.
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A review of the newly developed method used to prevent liquefaction of iron ore fines on bulk carriers
Liquefaction is a commonly occurring problem affecting solid bulk cargoes on board bulk carriers. If liquefaction of a solid bulk cargo occurs on board a bulk carrier it can result in the vessel listing or capsizing resulting in the loss of human life and industry assets. Recent incidents involving bulk carriers transporting iron ore fines have initiated research into, and implementation of, a new test method used to determine a safe moisture content at which it can be transported without being at risk of liquefying. The new test method, known as the ‘Modified Proctor/Fagerberg Test for Iron Ore Fines’, has been amended in the 2015 edition of the International Maritime Solid Bulk Cargoes Code and will be entered into force in 2017. The objective of this paper is to provide a review regarding the development of the Modified Proctor/Fagerberg Test developed by the Iron Ore Technical Working Group. The review focusses on the key findings from five publicly available reports released in 2013.
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Sampling Disturbance in Soft Ground: Implications in Geotechnical Design
This paper discusses the main mechanisms of sampling disturbance in soft ground and their implications in geotechnical design. In addition to the mechanical disturbance associated with the type of sampler, the influence of other factors frequently overlooked in practice such as thermal loading due to waxing as well as biological effects due to long-term storage, are evaluated. The paper discusses three methodologies for assessing sample quality in soft soils, which may be easily incorporated in practice. In the last section, mechanical soil properties derived from specimens retrieved using four different samplers are used in the prediction of the total settlement and excess pore water pressure underneath an embankment. The results of the prediction exercise demonstrate the negative effects of poor sampling in geotechnical design. It demonstrated that reliable and cost-effective predictions of geotechnical infrastructure are possible with minimum improvements to the current practice for sampling and testing of soft clays.
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Effects of preloading on soft clay improvement using deep soil mixing
Poor performing soils, particularly soft clays, are more prevalent around lakes and coastal environments, where demand for construction is generally higher. It is therefore critical that suitable ground improvement techniques be developed and refined to ensure these sites perform satisfactorily under applied structural loads. There is a clear trend in geotechnical construction to further develop technologies such as Deep Soil Mixing (DSM), using cement, lime, fly ash or bottom ash, with an aim to improve the mechanical properties of problematic soils. In this study, the influence of surcharge (10 kPa to 120 kPa) applied during curing on soil-cement columns is investigated using two different clay types, namely kaolinite and bentonite. Preload provides confinement and pre-compression during curing, which in turn increases the bearing capacity of the treated ground. The results of unconfined compressive strength tests are analysed to illustrate how the mechanical properties of the clays composed of differing cement content are influenced under varying surcharges applied instantly after mixing. The results indicate that mechanical properties of cement treated soft clays, including strength and stiffness can be enhanced through the application of surcharge immediately after construction, during the curing phase. This could potentially provide a cost effective and environmentally friendly alternative by reducing the required cement content being added to soil to achieve a given strength.