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Unsaturated free-standing mainline railway embankments – Part 2: An example of handling the awkward truth
The presence of negative pore pressures within cuttings and embankments, and the benefit of the consequent reduction of the likelihood of instability (also known as increased stability), have long been recognised by members of the profession. Negative pore pressures are usually a consequence of environmental influences upon clay soils in particular, and are frequently termed “soil suction”.
The recognition of suctions in the assessment of potential instability, by way of stability analyses, is less common, albeit that the tools are available to conduct such analyses, once the boundary conditions are understood.
Measurement of suction values in the field assists the selection of suction values appropriate for such analyses.
In the companion paper, the authors develop a philosophy and present a defensible model for analysis of free-standing embankments (Hull & Leventhal, 2019). Herein, a case history is presented that demonstrates one such analysis, being for Main Line Railway infrastructure. The results indicate the benefit accrued through recognition of suction in the estimation of potential instability of free-standing embankments.
The paper is intended to alert the profession to an improved assessment technique that incorporates these effects.
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Evaluation of changes of the Thornthwaite Moisture Index in Victoria
Climate change has become one of the most pressing environmental concerns and the greatest challenges to global infrastructure today. It has been demonstrated by many researchers that Victoria along with other Australian States and Territories has been experiencing a drying trend over the last several decades. Numerous lightly-loaded residential buildings constructed on expansive soils are subjected to distortions arising from differential ground movements caused by seasonal soil moisture changes. The climatic parameter, Thornthwaite Moisture Index (TMI) has been widely used by geotechnical engineers and practitioners as a means of classifying climatic zones and estimating the depth of design soil suction changes. The main aim of this paper is to evaluate changes of TMI index in Victoria in the past 60 years. Long-term (1954-2013) meteorological data from 70 weather stations across Victoria were employed to develop TMI isopleth maps for the three 20-year periods (i.e. 1954-1973, 1974-1993 and 1994-2013). The methodology and equations employed for TMI computation are presented and a worked example is provided as well.
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Reuse of Iron Exploitation Waste as a New Binder for Tailings Stabilisation in Dry Stacks: Circular Economy Approach
The dried allocation of the tailings, rather than the disposal in a slurry form, appears as an alternative to attend new legislation and improve the safety of mines operation. Also, the use of cementing agents in dry stacking facilities can enhance aspects of operations such as guaranteeing dilatant behaviour at the base and increasing tailings’ strength. The present research assesses the technical and environmental viability of a new alkali-activated cement (AAC) in iron ore tailings stabilization. The mechanical response of compacted tailings-AAC specimens was evaluated through strength and shear modulus tests while Life Cycle Assessment (LCA) was performed to verify the sustainability of this new binder when compared to conventional AAC. This new binder is derived from the residues of iron exploitation and is intended for use in new disposal schemes, such as dry stacks. The AAC is mainly composed of metakaolin (MK), produced from the residual soil removed during the mining activity, and sodium silicate (SS), produced with sandy tailings. Using tailings and waste in AAC production aligns with sustainable practices, minimizing resource consumption and promoting waste recovery. Also, LCA demonstrates a lower impact for tailings AAC when compared to conventional AAC. In addition to environmental and mechanical aspects, using this AAC supports the application of circular economy in mining since it enables the reuse of waste produced in mine operation as a substitute for conventional cement (that involves another industry and raw materials).
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A three dimensional model for the evaluation of resilient modulus of unbound granular materials
Resilient modulus is an important property that controls the performance of the subgrade and granular materials under repeated loading and is required for mechanistic-empirical pavement design. Technically, resilient modulus can be obtained from the repeated load triaxial test in the laboratory. Due to the time-consuming, complicated and expensive nature of the test, it is common to estimate the resilient modulus from other simpler approaches. Due to the discontinuous nature of the unbound granular materials, discrete element method has been used recently to predict resilient modulus for granular materials. It is clearly necessary that the proposed model be verified by comparing with the experimental results and there appears to be no validation against the experimental resilient modulus for these reported models. In this study, the laboratory repeated load triaxial test was carried out for one of the popular pavement materials used in Victoria, 20 mm class 1 crushed rock. The resilient modulus results were then compared with the result from the model. By restricting the rotational motion to simulate the interlocking effect of the particles, it was observed that the resilient behaviour from the model and the experimental test is almost identical.
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The mechanics of discontinua: Engineering in discontinuous rock masses
Rock masses are distinguished from most other engineering materials by their inherently discontinuous nature and by the range of scales on which discontinuities occur within them. The paper highlights a number of concerns that these factors pose in engineering practice. It reviews the basic mechanics of discontinua and the historical development of the characterisation, testing and analytical and numerical techniques available to the engineer working with discontinuous rock. The practical application of these techniques is illustrated by examples of their use in underground construction, caving methods of mining and hot dry rock geothermal energy exploitation. Despite the difficulties that still arise in engineering in discontinuous rock masses, it is shown that quite remarkable advances have been made in the last 40 years.
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Overcoming the Current Density Testing Impediment to Alternative Quality Testing in Earthworks
Density testing has been applied widely in earthworks quality assurance (QA), yet because of its widespread usage, this now acts as an impediment to the development of alternative methods of testing. Many incorrect inferences are made from density testing. Modern geotechnical and pavement designs are based on modulus and strength values. However, when such measurements are correlated back to density testing, a poor correlation often results. Therefore, while alternative in situ testing to density provides significant benefits to the industry, the poor correlation is often questioned, and then site personnel default to the usual density testing for quality testing of earthworks. The reason for the poor correlations includes, the depth of influence being different, with the quality and compaction being combined into one parameter (say modulus). Another rationale for the poor correlation, is the density lot measurements are normally distributed due to its low coefficient of variation, while other measurements are not normally distributed and have a large variation. A new method on matching Probability density functions (PDFs) for quality assurance has been successfully used on a large earthworks project to overcome the correlation inconsistency and is introduced. Data from several test sites using a range of alternative testing equipment are compared. One must also distinguish between a test accuracy and its precision. Traditional testing density has focused on its key benefit of precision without appreciating the poor accuracy associated with this measurement. Case studies are used to illustrate this dichotomy between traditional and non- traditional testing for QA assessment of earthworks.
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Estimation Of Travel Distance For Landslides In Soil Slopes
Methods for prediction of the post failure travel distance for landslides from cuts, fills and natural soil slopes are presented. The methods first require assessment of the likely mechanics of initial sliding, based on the material properties and slope geometry with a view to identifying if the subsequent travel of the landslide will be “rapid” or “slow”. The post failure travel distance is then estimated for “rapid” slides from consideration of the slide mechanism, material type, slope geometry and/or slide volume; and for “slow” slides based on the residual factor of safety and estimated surface of rupture.
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Characterisation Of Complex Ground Conditions For The Rozelle Interchange Project
The Rozelle Interchange Project (RIC) in Sydney is an underground motorway interchange connecting multiple underground and surface arterial roads as well as the future Western Harbour Tunnel and Beaches Link. RIC completes the WestConnex program of works and is a complex array of approximately 22 km of multiple level tunnels, all constructed in an area 2.5 km long and 1.5 km wide.
RIC is located within complex ground conditions that include deep soils, regional faults, structural zones and igneous intrusions. Deep natural soils infilling a valley near Rozelle Bay are mostly recent Holocene alluvial, marginal marine and marine deposits. These soils are interlayered, discontinuous, normally to slightly over consolidated and capped by sand and coarse rockfill from 19th century reclamation.
There is a strong contrast in the level of detail between borehole and CPT data. Distilling this to provide a geological and geotechnical model for a project wide interpretive report for designers of multiple structures required a hybrid approach to model presentation. This included providing a simplified graphical model and including details from specific investigations and laboratory testing allowing designers flexibility to adopt appropriate parameters for their specific application.
Similarly, the rock structural model evolved from development of structural domains to identification and inclusion of regional geological structures overprinting the structural model. Regional scale thrust faults, corridors of structural complexity and igneous intrusions were identified and refined prior to and throughout the design process. These were considered in the design by modification of excavation sequencing and changes to tunnel support.
Tunnel excavations encountered these regional features at the locations predicted and with similar character as those described in the model allowing the safe construction of the tunnels.
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Establishing Professional Accreditation Pathways for Australian Engineering Geologists in the Civil Design and Construction Industry
Recognition of the role of engineering geologists within the Australian civil industry is becoming increasingly important as the number of large- scale projects with complex ground-related risks increases. By their very nature, these projects require a deeper understanding of the ground to form the basis of sound and appropriate engineering solutions.
Application of specialist engineering geology expertise is ever more important as Australia embarks on a significant transition to renewable energy production. By way of example, pumped hydro energy schemes (PHES) require a multitude of civil engineering structures for which engineering geologists are required to develop ground models and identify geotechnical risks for tunnels, caverns, shafts, dams, roads, excavations, slope design, geohazard management, portal transitions, and earthworks. As the demand for civil-focussed engineering geologists in Australia grows, the significance of an established professional accreditation pathway becomes progressively more relevant.
Formal recognition as a chartered or registered professional signifies to clients, regulators, employers, and the public a demonstrated level of competency and experience. It requires a commitment to industry standards, continual professional development (CPD) and an enforceable code of conduct. It sets guidelines on professional conduct and establishes a benchmark for assessing key professional competencies and experience in a field of practice. The significance of achieving professional accreditation status facilitates recognition of engineering geologists’ valuable role in the Australian civil engineering industry.
By way of clarification the definitions below reflect the terminology used in this editorial:
- Chartership – the highest available technical credential as a professional. Recognised nationally and internationally and represents a certain level of qualifications, competency and practiced experience.
- Registration – formal recognition of qualification, competency and professional experience. Satisfies state and/or national legislated requirements for practising professionals.
- Licence – a term equivalent to registration, but not commonly used in Australia.
- Accreditation – a general collective term of formal professional recognition which includes all those categories listed above.
Currently, in Australia, there are no competency-based chartership routes specifically for the engineering geology discipline and administered by relevant Australian professional organisations. Comparison with existing international engineering geology charterships, registration or licensing schemes highlights the present lack of professional recognition of engineering geologists within the civil construction sector in Australia.
This editorial piece presents the local and international professional recognition pathways currently available for engineering geologists along with their benefits and challenges. It introduces the present state of practice in Australia with respect to recognition of engineering geology as an independent discipline and compares this with established global schemes as well as domestically within the mining industry.
The challenges faced in achieving existing accreditation routes within Australia is discussed. The lack of professional accreditation for engineering geologists can be a limiting factor in career development within the discipline. As well as impacting upon the individual engineering geologist as a professional, there can also be flow-on effects to the engineering design. For example, the absence of accreditation standards can potentially lead to increased project risks or perhaps more conservative designs. This editorial discusses the absence of accreditation for engineering geologists in the recently introduced state- based Registered Professional Engineer (RPE) legislation policies for the infrastructure industry, and what this might mean for the practicing individual. Specifically, this relates to potential and perceived limitations in career opportunities and development, as well as potential future consequences for the industry more broadly, which may discourage new entrants to the profession.
There will always be ambiguity when there is a large overlap between two competencies such as geotechnical engineering and engineering geology. Recognising this, we conclude the editorial with proposed accreditation pathways for the practicing engineering geologist in Australia. To achieve best practice in Australia, engineering geology should be identified as an independent discipline as is standard in many other countries.
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Layer Identification and Strength Interpretation in Clay from Penetrometer Data
Penetrometer tests are used widely for offshore in situ site investigations and for soil characterisation in laboratory model tests. This paper presents a summary of two PhD dissertations and the work of a Research Fellow on penetrometers in layered clays. The continuous penetration responses of the commonly used cone penetrometer; and two increasingly used full-flow penetrometers (T-bar and ball) have been explored. Single layer, two-layer (soft-stiff and stiff-soft) and three- layer (soft-stiff-soft and stiff-soft-stiff) clay deposits have been considered. The investigations have been carried through large deformation finite element analyses and centrifuge model tests. Interesting and critical soil failure mechanisms are illustrated. Design frameworks are provided for the identification of layer boundaries, and interpretation of undrained shear strength of each identified layer.