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On the common criticism of initial moisture content bias in the shrink-swell test
The shrink-swell test, and its application in site classification and foundation design according to AS2870 (2011) has both advocates and critics. It has been used as the basis for many residential foundation designs in Australia for more than 30 years, and although examples of performance failures in residential structures are familiar to most practitioners, the incidence is relatively low compared with the number of structures that are constructed, and substantiated examples of widespread and systematic failures due to poor foundation design are few and far between. Nevertheless, there are those who advocate that the shrink-swell test is fundamentally flawed, generally on the basis that the reactivity index that results for any particular soil is affected by the water content of the soil at the time of measurement. Whilst there is anecdotal evidence to suggest this, the data usually put forward to demonstrate this assertion are seldom of high scientific quality, and not obtained under conditions that would allow the assertion to be rigorously and conclusively tested. In fact, scatter plots of shrink-swell index vs initial water content often put forward (eg Rogers and McDougall, 2020) as evidence do show a tendency for soils with higher water content to have higher shrink-swell index values, however, this paper demonstrates that this should actually be expected, and it does not, in itself, confirm that there is bias in the test. The paper discusses the alternative of basing foundation design on Atterberg limits, and recognises that whilst these give a good indication of the clay type and clay content of a soil, as they are determined on remoulded samples, they cannot account for soil structure which is a significant controlling factor in reactive soil behaviour. It goes on to consider what it would take to produce convincing data to demonstrate bias in the shrink-swell tests, and what would be needed to conclusively demonstrate that an alternative approach to site classification was more reliable.
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Geotechnics offshore Australia – beyond traditional soil mechanics
This paper provides an overview of current research into, and practice of, offshore geotechnics in Australia. Offshore geotechnics is a specialism within geotechnical engineering, and offshore geotechnics in Australia involves a further level of specialism, associated with the carbonate soil conditions found across our oil and gas development regions.
The geotechnical challenges faced by Australia’s offshore developments are continually evolving as exploration moves from shallow to deep water and the types of offshore facilities evolve. Previous projects in shallow water have led to the development of new piled foundation design methods and construction technologies, and have generated new solutions suited to local soil conditions, such as shallow cemented layers. Current research is now mainly focused on deep water sediments, anchoring and shallow foundations (rather than piled foundations), long pipeline networks and the geohazards faced beyond the continental shelf. Examples of research and novel design practice show that much of this technology lies beyond traditional ‘text book soil mechanics’. Defining characteristics of the deepwater frontiers include large deformations and transforming soil properties.
These challenges open up refreshing new avenues of research, and provide exciting challenges to the designer. Driven by these local needs, Australia is recognised globally as a leader in offshore geotechnics, and many of the technologies presented in this paper have become Australian exports into global practice.
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Evaluating liquefaction and lateral spreading in interbedded sand, silt and clay deposits using the cone penetrometer
Current procedures for evaluating potential earthquake-induced liquefaction and lateral spreading appear to have a tendency to over-predict liquefaction effects in interbedded sand, silt, and clay deposits. Possible reasons for overprediction of liquefaction effects are discussed, and investigations regarding some factors pertinent to use of the cone penetrometer are described. An axisymmetric direct cone penetration model is presented for use with the MIT-S1 constitutive model to explore cone penetration processes in a range of soil types; current efforts are focused on validating this new direct cone penetration model, beginning with simulations of cone penetration in soft clay. The relationship between cyclic strength and cone penetration resistance in non-plastic and low-plasticity fine-grained soils is examined by relating cyclic strengths from laboratory tests to cone penetration resistances from simulations. The performance of a site underlain by interbedded soils along the Çark canal during the 1999 M=7.5 Kocaeli earthquake is analysed using one-dimensional lateral displacement index procedures and two-dimensional nonlinear deformation analyses with spatially correlated stochastic models to illustrate how several factors can contribute to an over-prediction of liquefaction effects. Future research needs and directions for improving the ability to evaluate liquefaction effects in interbedded sand, silt, and clay deposits are discussed.
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Moisture Movement Analyses For Coal Stockpiles
Flowslides and stability issues have occurred periodically within stockpiles of coking (metallurgical) coal at coal processing plants and export terminals in Queensland’s Bowen Basin, and to a lesser degree in New South Wales, since the early 1970s. A description of the issue and summary of research at James Cook University from 1973 to 2000 was published in ACARP Report C4057. Despite this work, coal stockpile flowslides remain a significant risk at mine and port stockpiles due to their initiation without warning and dramatic consequences. To be able to adequately model the redistribution of moisture that leads to collapse of a stockpile and then conduct realistic stability analyses for design of preventative measures remains an elusive prospect.
This paper therefore updates the previous work with results from SEEP/W transient seepage modelling within a 12m high 14,700 tonne coal stockpile constructed at Hay Point in late 1991 for which initial moisture content, pore pressures at the stockpile base, outflows from subsoil drains and final density and moisture profiles were measured. The model was based on results of laboratory permeability and column drainage tests on specimens taken from a composite bulk sample obtained at the time of stockpile construction. The coking coal product was from an operation with a known history of stockpile instability. Results were found to correspond well with pore pressures measured at the stockpile base and the stockpile’s final moisture profile provided account was taken of a thin higher permeability zone just above the subgrade.
The approach adopted and parameters developed provide a significant advance in modelling of moisture movements within production coal stockpiles, with a view to subsequent slope stability analyses.
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Practical Considerations For The Application Of A Survival Probability Model For Rockfall
Rockfall fragmentation is a common and very complex phenomenon that is still inadequately understood and rarely modelled. When falling rock blocks break upon impact, their shape and size change and the kinetic energy is distributed amongst fragments. To efficiently design mitigation measures, it is necessary to adequately account for fragmentation when modelling rockfall trajectories. To do so, a better understanding of the fragmentation process, its occurrence and its likely outcomes is needed. The authors have recently proposed a novel model which can predict the survival probability (SP) of brittle spheres upon impact from the statistical distribution of material parameters, obtained by standard quasi- static tests (Brazilian tests and unconfined compression tests). The model predicts two Weibull parameters (shape parameter -m- and scale parameter – critical kinetic energy) that are used to define the SP. The model is based on theoretically-derived (from Hertzian contact theory) conversion factors used to transform the critical work required to fail disc samples in quasi-static indirect tension into the critical kinetic energy to cause failure of spheres at impact in vertical drop tests. The objective of this paper is to provide some practical insights into this model in relation of the analysis of the Brazilian test results and the number of Brazilian tests required to achieve an acceptable prediction. A first analysis highlights the importance of distribution of forces required to break the specimens in Brazilian tests and a common statistical based outlier removal methodology was applied to reduce the experimental error associated with the operator. After eliminating the outlier data, the quality of prediction is improved and, in particular, the influence of the specimen diameter used in Brazilian compressions to derive the model input parameter is significantly reduced. This latter point implies that the size effect is adequately captured. The second analysis reveals the highest variability for batches with low number of tests and a progressive reduction as the number of sampled test increases. Based on these results, it is suggested to use at least 30 Brazilian tests and remove outliers using the simple statistical approach presented in the paper (with of 0.5 or 1.0).
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Intelligent Prediction Models For UCS Of Cement/Lime Stabilized QLD Soil
The study aims to develop proposed predictive formulas for determining the unconfined compression strength (UCS) of cement/lime stabilized Queensland soil based on Multi-Gene Genetic Programming (MGGP) and Artificial Neural Network (ANN). The models evaluate the effect of three independent variables, including the binder type (cement and lime), the binder content, and the curing time, on the UCS of the stabilized soil. The results show that the selected optimal MGGP and ANN models can predict the target values with high correlation coefficients (R-value approximately of 0.992 and 0.998, respectively), and low errors (e.g., RMSE and MAE). The sensitivity analysis of the MGGP and ANN models provide the same results, in which the curing time has the greatest influence on the UCS value, followed by the binder content and binder type. The performances of the MGGP and ANN models are compared based on statistical parameters, several external criteria, and distribution properties. The study finds that both models show their generalization capabilities with robust, powerful, and accurate prediction ability; however, the ANN model slightly outperforms the MGGP model. The proposed predictive equations formulated from the selected optimal MGGP and ANN models could help engineers and consultants to choose the suitable binder and the reasonable amount of binder in the pre-planning and pre-design period.
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Problems with liquefaction criteria and their application in Australia
In many parts of the world, including Australia, the state of practice in assessing if liquefaction will occur is based on the recommendations of Youd et al. (2001) which arose from workshops convened in the United States by NCEER (now MCEER). In some regards, the final publication did not so much represent a consensus view as a compromise between differing opinions within the expert group. Since then, disagreements over key aspects of liquefaction assessment in North America have increased to the point of chaos (Youd, 2011). There is little awareness in Australia of this situation nor appreciation of the NCEER limitations in applying these recommendations. Poorly informed decisions are increasing costs and causing project delays. This paper presents no original research but is an attempt by a practising geotechnical engineer to point out some problematic aspect of the NCEER liquefaction criteria, and of current recommendations in the literature and in so doing to encourage other practitioners and regulators to consider reasonable adjustments or alternatives.
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Australian Engineering Geology – State Of The Art
Engineering Geology is the science devoted to the investigation, study and solution of the engineering and environmental problems which may arise as the result of the interaction between geology and the works and activities of man, as well as to the prediction and of the development of measures for prevention or remediation of geological hazards (IAEG, 2024).
Engineering geology is an essential input to geotechnical engineering for the simple fact that without geological input or an engineering geological model there is nothing to base the engineering upon. Whilst there is appreciable overlap between the skillset possessed by the geotechnical engineer and the engineering geologist, it is the engineering geologist who brings an understanding of earth processes, and geological history to the development of the ground model, and it is the engineering geologist who through their understanding of natural processes identifies and assesses geological hazards to the project.
The geology of Australia includes virtually all known rock types, spanning a geological time period of over 3.8 billion years, including some of the oldest rocks on earth. It is a complex geological setting, with complex geological processes acting which makes the need for sound engineering geological input to our projects all the more critical.
The inherent Australian landscapes provide a myriad of both typical and atypical natural geological and geomorphological characteristics, with a rich history of landform development associated with changes in facies and structural controls overprinted by a unique set of Quaternary conditions, with many areas affected by relatively recent (in geological time) volcanic activity.
The transported and/or parent rock weathered derived soils forming the uppermost strata in many places include common varieties (alluvial, colluvial, estuarine, marine, aeolian, residual) and uncommon types such as duricrusts, reactive, sodic and acid sulphate soils. These uncommon types of soils provide challenges to the design and construction of the built environment in terms of their potential for reuse, taking into consideration sustainability, as well as their actual behaviour as a result of natural or anthropogenic changes or impacts.
The importance of the Engineering Geology discipline to Australia is significant and is often misunderstood and/or under-valued, both by government, construction and mining-based industries, learned societies and Academica alike.
Engineering Geologists have, continue to and will in the future, play key roles, in the development, and often through the full life cycle, of major infrastructure projects covering the full gambit of urban or greenfield terrestrial and marine environments in this country. From the concept level in terms of review of existing information and remote sensing; through to site reconnaissance and mapping; designing, managing and interpreting associated geotechnical investigations; geological and geotechnical model development; design parameter definition and ground behaviour analysis; assessment of construction materials; earthworks, slope stability and natural terrain hazard assessment, as well as associated risk management and the derivation of mitigation measures/strategies, all fall under the sphere of the discipline.
Often engineering disciplines outside the realms of ground engineering, as well as client organisations and/or decision makers, do not have the necessary knowledge/experience to differentiate between the skill sets of Engineering Geologists and Geotechnical Engineers, and for the most part they don’t need to – as far as they are concerned, they need to get ‘geotech’ done.
If one considers ‘geotechnical practice’ or ‘geotechnics’ to encompass the range of geological and engineering skills necessary to service projects, then skills in geotechnics can be considered to cover a spectrum between geological skills, typically taught through geoscience education, and engineering skills taught through an engineering education. Most, if not all geotechnical practitioners have at least an awareness of the skills brought by their counterparts – engineering geologists have at least an awareness of geotechnical engineering and geotechnical engineers have at least an awareness of engineering geology. However, within the geotechnical profession there are practitioners who through further study or vocational training advance their skills further along the spectrum. There are practitioners with geoscience backgrounds competent to perform what might traditionally be considered engineering functions and vice versa, engineers competent to perform what might traditionally be considered geological functions. This is a wonderful characteristic of the geotechnical profession. It brings together people with backgrounds in science and engineering, their skills are combined to provide ‘geotechnics’ and there are opportunities to develop new skills throughout a career in the field.
Simplistically and traditionally, Australian educated Geotechnical Engineers are more likely to have followed a hybrid path studying both civil/structural engineering aspects coupled with specific units or modules in geotechnical engineering such as earthworks, foundation design and earth-retaining structures. They may be more focussed on soil mechanics and the associated behaviour of pedological strata (soils) and may typically lack knowledge of the fundamentals of geology such as the theory of super-position and structural geology. In this way the role of Engineering Geologists generally lies in the methods required to “read the landscape”, define associated ground models, understand how the ground might respond to change caused by a project and how the ground might impact on a project and to offer solutions to manage the ground response. The engineering geologist can also bring knowledge of rock and its weathering profile and engineering behaviour that is generally lacking from Australian engineering education.
Often Engineering Geologists are the first to site with critical inputs into the actual early decision-making process and the development of projects in terms of their locality, form and the approval of funding for later design phases, as well as if projects are ultimately built or not. Their influence on the cost and direction of projects can be very significant – for example the development of a sound conceptual ground model early in a project could lead to a decision to align a tunnel through better ground or perhaps not tunnel at all which could have significant impact on subsequent design and construction costs.
The criticality of the accuracy and representativeness of baseline ground conditions derived from good landform analysis, understanding of geological history and processes, supplemented by site investigations cannot be underestimated. This information is used to inform model development, design parameter definition and associated ground behaviour assessments which has a direct bearing on the appropriateness of the associated design of works, related relevant construction methodologies, programs and costs. This means that if the factual information and its interpretation is not satisfactory this can and has led to exponential problems (including potential health and safety risk) through a project life cycle which has often resulted in costly and adversarial legal disputes not just in Australia but internationally. The added focus on the importance of Engineering Geology in this context cannot be underestimated as Australia is fast approaching, and if not has overtaken, the US in terms of proportional litigations for construction projects including and often related to claims of “unforeseen ground conditions”.
With the importance of Engineering Geology to the development of key infrastructure and therefore its impacts on the Australian community as a whole, it is disheartening that the discipline in Australia is at present only offered at tertiary educational level as modules, without the re- establishment of standalone either undergraduate or postgraduate courses being offered. The problem is further compounded by the fact that there is no professional registration scheme available in Australia that recognises the discipline in its singularity and therefore its importance, being absorbed into geotechnical engineering professional qualifications, where candidates have been deemed to follow university degrees in line with the “Washington Accord”. There are therefore a significant number of practising Engineering Geologists in Australia providing key inputs to projects that are presently marginalised in terms of the recognition of their critical skillsets to geotechnics and to various industries. The situation may become worse in the near future with seemingly a complete non-recognition of the discipline and its importance within the present Registered Professional Engineer schemes that have been enacted into legislation in certain States, which could be followed in the same vein soon by the remaining States and Territories.
In addition, the tandem effects of the lack of taught courses coupled with the lack of professional recognition and registration, and therefore a clear path of career development, may mean that the actual discipline could be considered as on the “endangered” list and liable to extinction in the future much like the dinosaurs that are often encountered around Winton in Central Queensland. A significant step change is therefore needed by decision makers in recognising the critical value that the discipline brings to the development of our society with the provision of the necessary education, training and professional pathways to encourage future Engineering Geologists to start and ultimately fulfill a very rewarding and significant career. The geotechnical profession is simply not complete without its geological component, and the consequences of that can only be dire.
The Australian Geomechanics Society recognises the importance of Engineering Geology to the Australian society, which has formed the basis of this themed issue that also celebrates the 60th anniversary of the foundation of the International Association for Engineering Geology and the Environment (IAEG). The papers/editorials presented in this Special Edition cover both the aforementioned problems of establishing professional pathways for Engineering Geologists in Australia, as well as showcasing the variations in geology over the Continent and the associated risks and mitigation measures and designs/approaches to deal with their inherent characteristics.
The link between the provision of appropriate education/training and registration for Australian Engineering Geologist is mutually exclusive, which has been attempted to be encapsulated in Figure 1. These issues are felt to be of such criticality to the discipline in terms of its place and development in our society, that as part of this Special Edition separate and stand-alone editorials are provided at the front of this publication, exploring in more detail these issues, before the presentation of technical papers.
In terms of registration for Engineering Geologists in Australia, existing avenues do presently exist with in-country and international learned societies. However, their registration requirements and the value they bring to practising Engineering Geologists, in terms of technical recognition and associated “formal signoff/approval” rites and associated responsibilities, within the Construction/Infrastructure industries are varied. In many cases existing practitioners either do not have the right academic qualifications and/or there is a lack of industry/governing authority recognition of the registrations being presently offered (see Figure 2).
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Ground conditions and building protection for the New MetroRail City Project, Perth
The New MetroRail City Project is due for completion in 2007 in Perth, Western Australia. The project included construction of two underground stations, twin bored rail tunnels of 1.4 km combined length and cut and cover tunnels and dive structures of about 1 km total length. It is the first major underground construction project within the Perth Central Business District. This paper provides an introduction to the project, describes the geology and hydrogeology of the area and summarises geotechnical design parameters for the various geological units encountered. The paper presents parameters adopted for design of temporary and permanent works for the project, the selection of which was governed by the constraints of this project. The values adopted may not be the ‘best estimate’ values of these parameters, but rather reflect a degree of conservatism appropriate to a project such as this. The parameters may not be appropriate for other projects in the Perth CBD. Ground conditions vary significantly along the alignment from soft estuarine muds in an area of reclamation to very dense cemented sands and very stiff to hard clays. Deep foundations for the project extend down into the bedrock below the CBD, a Tertiary siltstone/sandstone. Key geotechnical hazards encountered during the project are discussed. The building protection methodology on the project is described, including damage assessment, condition surveys, monitoring and protection of key structures.