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Characterisation of ground conditions to reduce risk for building footing design in Melbourne, Victoria
Footing systems for many of Melbourne’s tall buildings are rarely governed by their ultimate capacity, rather, the allowable displacement of the footing system is likely to be the primary consideration. An appropriate geotechnical investigation must therefore assess the stiffness characteristics of the in situ ground, and in particular the founding materials that support these footing systems. In order to further characterise ground conditions and better manage ground risk, in situ pressuremeter testing can be used in conjunction with more traditional investigation methods and verification activities during construction to provide prudent yet not overly conservative geotechnical advice and design for these developments. This paper discusses two case studies comprising historical geotechnical investigations for buildings in Melbourne, where the use of pressuremeter testing in conjunction with traditional investigation methods have provided greater confidence on the deformation behaviour of founding conditions. This paper sets out how the results from the investigations were used to inform footing solutions to be designed and subsequently constructed, as well as discussing the value of verification activities to confirm design assumptions, further reducing the ground risk during construction and realising efficiencies in the footing design.
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Deep Wet Soil Mixing Columns Ground Treatment Technique-lesson Learnt From Project
Deep Wet Soil Mixing (WSM) ground treatment columns have been designed and constructed first time on TfNSW Lisarow to Ourimbah Stage 3B project to meet performance requirements for embankment and retaining wall foundation. However, during construction, the project faces a number of challenges such as reuse of several thousand cubic meter of soil-cement mixed waste material produced from WSM construction, various quality control testing issues and construction difficulties arising from interlayered stiff/dense soil. Hence, the project team developed extensive field trials and innovative solutions to mitigate all these challenges. Instrumentation monitoring results obtained from settlement plate, inclinometer, piezometer, survey plugs and wall tags suggested that primary consolidation settlement of the WSM treated ground is virtually completed within one month after the construction. Field monitoring results also reveal that settlements and lateral movements of the bridge approach embankments and hybrid retaining wall (Reinforced Soil Wall combined with L-shaped wall) foundations are much less than the predicted design values. In addition, the trend of the 12 months monitoring results provides confidence on the long-term performance of these structures, which is expected be smaller than the predicted values. Furthermore, it is revealed that about 5000m3 of soil-cement mixed waste material/spoil have been recycled, and used successfully as fill materials for various civil engineering applications at the project site. Following the several field testing regime, it is concluded that only Unconfined Compressive Strength (UCS) testing from the cored samples is the most reliable quality control measure for high strength WSM materials. In addition, strength and deformation parameters of the field core samples are proven to be increased with the increase of curing time. Hence, it is recommended to include curing effects on the design of deep soil mixed columns ground improvement technique for future projects.
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Determination Of Moisture Content Of Subgrade Soil Using Artificial Neuro-electronic Control
Moisture content of soil is of utmost importance in the progression of road construction and is absolutely crucial for making decisions concerning design and construction of pavements. Pavement sustainability depends on the performance of its individual components, which require the assurance of qualities such as evaluation of the properties of soil and constant monitoring of some soil conditions (e.g. moisture content). For pavement design the most considerable engineering factor of soil is the strength that is practically accomplished by soil compaction and soil stabilization. However, to achieve the required soil strength, consideration of compaction effort or stabilization ingredients should be precise, and it is inevitably related to the moisture content of soil. Hence moisture content determination is elemental and must be performed frequently as necessary. The conventional method for its determination involves oven drying and this endeavour is time consuming (requires approximately 24 hours for drying), which may affect the subsequent undertakings. Some microwave oven based fast methods have been realized recently but these require continuous manual interventions. In this paper, a new approach will be proposed in a view to suppress the limitations of existing methods while maintaining the better accuracy. This innovation embeds an automatic electronic control as well as an artificial neural network (ANN) in the framework for time optimization. Artificial neural network and automatic electronic control both together can be termed as artificial neuro-electronic control. The artificial neural network has been optimized and trained by mapping the weights of soil samples at specific time steps to the respective final moisture contents. As a result, subsequently the system can be able to predict the final moisture content by analysing fewer data samples in the very beginning of moisture content determination tests. Validation of the predictive results has also been conducted in real time for soil samples suitable for subgrade layer of a pavement to ensure the system feasibility for laboratory and field uses. Experiments show that this fully automatic system can exhibit a significant accuracy and precision for the evaluation of moisture content in about 50% reduced time compared to the standard microwave based method.
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2020 AGS Victorian Symposium
Sustainable Geotechnics – Excellence in Planning, Design and Construction
Professor Arul Arulrajah, Patrick Wong and Ross Roberts
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Frequency Of Landsliding As Part Of Risk Assessment
An integral part of systematic risk management for landslides is the assessment of landslide frequency. Qualitative approaches have frequently been used for landslide risk assessment but there is now an increasing trend towards quantitative assessments. In Australia, this has been highlighted by the publication of a comprehensive paper by the Australian Geomechanics Society in March, 2000. This paper replaced an earlier 1985 publication which provided guidelines and recommendations for qualitative risk assessment based primarily on site inspection, previous experience and engineering judgment.
The assessment of landslide risk requires assessment of hazard, elements at risk and the consequences of landsliding on those elements. Attention must be given to the mobility of a landslide as well as to the vulnerability of elements at risk before the consequences can be assessed reliably. A hazard-consequence matrix approach is often a convenient framework for an integrated approach to risk assessment on a qualitative or quantitative basis (AS/NZS, 1999; Flentje et al 2000; Walker et al., 2000).
The first important stage of any investigation concerns the assessment of landslide hazard which is often influenced by a range of factors. It is important to consider the basic causes and mechanisms of slope instability as well as the triggering factors. For example, the most common natural triggering factor in Australia is rainfall. Therefore, frequency of landsliding is often closely related to the intensity and duration of different rainstorms.
This paper will discuss different aspects of a landslide risk assessment task with particular reference to quantitative assessment of the frequency based on historical and observational data. Reference will be made to the monitoring of surface and subsurface movements and piezometric levels as well as to the detailed historical and spatial analyses of rainfall records.
The procedures and methods proposed in this paper will be illustrated with reference to two case studies. Both of these case studies are defined as ‘slide’ category (Cruden and Varnes, 1996) landslides and it is important to note that this paper is directed at the assessment of this type of failure mechanism.
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Recent Advances In The Usage Of Recycled Materials In Transportation Geotechnics
Priority waste materials currently generated in Australia include construction wastes, demolition wastes, glass fines, waste tyres, plastics, industrial wastes and organic wastes. The increase in generation of these wastes has led to significant research over the past decade on the reuse of recycled waste materials in geotechnical engineering applications. An estimated 7.9 Mt of wastes, which accounts for 36% of Australia’s current annual landfilled waste, have the potential to be diverted into civil engineering applications, such as for the construction of roads, railways and land reclamation projects. Recycled materials have been evaluated in the laboratory and new specifications successfully developed, to incorporate their usage in pavement geotechnology and ground improvement applications. Recycled materials are increasingly being used in unbound and stabilised pavement applications. In addition, industrial wastes such as fly ash and slag have also been evaluated in recent years as alternative binders to cement in pavement and ground improvement applications. This paper discusses recent advances in the usage of recycled materials in transportation geotechnics, with reference to case studies of recycled materials usage in Australian projects. Ground improvement projects, comprising of the installation of ground inclusions in waste materials, in an international railway and an airport land reclamation project are also discussed.
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Connecting geotechnical investigations with project risk
It is often stated by geotechnical engineers that a project pays for a site investigation one way or another as a means of justifying a scope of work aimed at managing a project’s risk. This proposition is critically assessed through reviewing three case histories covering site investigations performed for design only, design and construct, public private partnership (PPP) and alliance contract models. An extensive site investigation was performed for the Ballina Bypass Alliance project. Most of the project risks were identified and managed. However, some risks were realised relating to detecting palaeochannels, variable subsurface topography, quantifying material parameters and coping with corestones. An extensive site investigation has been performed for the Snowy 2.0 project, but its scope has been limited by time and access constraints. Risk is managed through adoption of a geotechnical baseline report. Site investigations for Inland Rail for design only, design and construct and PPP contract models have been scoped and partially delivered. In addition, Inland Rail has developed an earthworks materials specification that can be varied to suit site characteristics. Integration of site investigations with the specification and design is shown to be key to controlling the major materials risk. Some thoughts about scoping an investigation to inform geotechnical risk when procuring a PPP are presented. Overall it is concluded that the geotechnical industry generally scopes investigations to adequately manage risk. Quality is shown to be as or more important than quantity. The critical importance of engineering geology for identification of potential risks is demonstrated thus allowing a focussed drilling and geophysics scope to be delivered. Challenges remain when communicating residual risk to stakeholders.
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Probabilistic methods for slope analysis and design
Probabilistic methods combined with risk assessment are a better way to assess slope design in open pit mines compared to deterministic methods. These methods are suitable for use on evaluation of risk or when there is uncertainty in the input parameters.
Probabilistic analyses require more computer power than deterministic analysis. In many case a probabilistic analysis requires ten to thousands more computer resources than an equivalent deterministic analysis. Methods like Monte Carlo simulation (MC) may require thousands of analyses depending on the number of variables considered in the model. Other methods like First Order Second Moment (FOSM) or Point Estimate Method (PEM) and may require tens to hundreds of analyses.
Monte Carlo simulation is applied routinely today on simple analyses like wedge stability or limit equilibrium analysis; current computers can carry thousand of analyses in a relatively short period of time. This is not the case when more complex models are built like 3D models at mine scale including complex mining sequences, or dynamic analysis of a 3D model. Large scale models can run for hours even in fast computers. Where the Monte Carlo method is not an option other alternative methods should be used.
This paper compares four different methods and presents the equations required to use a Modified Point Estimate Method (mPEM) presented by Harr (1989). The methods are compared using simple examples in the paper. Recommended probabilities of failure for open pit design are also presented.