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Assessment of the impact of climate change on expansive soil movements and site classification
There is overwhelming evidence that climate change leads to a wide range of climatic and weather changes that can affect the performance of built infrastructures. Climate change is likely to have significant impacts on the performance of residential buildings constructed on expansive soils. The Thornthwaite Moisture Index (TMI) as a useful climate parameter has been widely employed to estimate the depth of design soil suction change (Hs) which is needed for the determination of characteristic ground movement (ys). Precipitation and temperature are the primary weather parameters required for the TMI computation. By applying the projected rainfall reduction and temperature increase in 2030, 2050 and 2070 in the TMI calculations, the effects of climate changes on expansive soil movements and site classification can be quantified by the use of the predicted TMI. In this study, TMI values of various areas of Victoria were calculated under A1B and A1FI emission scenario using climate projections generated from 23 climate models. These predicted TMI indices were then used to delineate TMI isopleth lines on the map of Victoria to visualise and compare climate conditions in 2030, 2050 and 2070. A case study was also carried out to assess the effect of climate changes on the magnitude of ground surface movements in the top five most densely populated cities (i.e. Sydney, Melbourne, Brisbane, Perth and Adelaide) in Australia for three specific years (i.e. 1990, 2030 and 2070). The results show that both Hs and ys values are expected to increase significantly with climate change.
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Engineering properties of the Newer Volcanics basaltic clays
The Newer Volcanic basaltic clays, weathered from the Newer Volcanics basalt rock, are commonly found to the north and west of Melbourne. As the Newer Volcanic basalt flow was the predominant overlay rock in the Western and Northern suburbs, the weathered basaltic soil is at a prime depth for shallow foundations of light structures. These basaltic clays can cause significant engineering problems for light structures and buried infrastructure. The shrinkage and swelling of basaltic clays due to seasonal moisture content change can damage light structures and buried infrastructure by movement in the foundation base and subsequent building movements. These movements can result in cracks and fissures within the clay as well. To date the weathering and soil formation, Atterberg limits and compaction efforts are well known for typical Victorian basaltic clay, however testing information is rarely published, and to a lesser extent mineralogy, soil strengths and swelling of the clay are not well documented. This paper discusses the reactivity of basaltic clays and examines engineering properties of the Newer Volcanics basaltic clays in Victoria based on previous testing and literature. The properties are: Atterberg limits, mineralogy, shear/ tensile strength testing, drained friction angle, permeability, suctions and shrinkage testing. Data are combined from testing and from literature conducted throughout Victoria.
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The Use Of Fractal Theory And Soil Index Properties To Infer The Soil Water Retention Curve For Low And High Plasticity Clays
Four fine-grained soils from South Australia containing differing particle size distributions were tested for their soil water retention properties. Despite their wide-ranging index properties, the samples from all four sites were confirmed to contain fractal particle size distributions (PSD) from sieve and hydrometer testing. Air entry values were obtained for each site from soil water retention curves (SWRC) that were generated using an unsaturated triaxial device with a pore air pressure/volume controller and a high air entry porous disk, which confirmed all sites contained fractal pore size distributions. The fractal dimensions of the particle and pore size distributions were not equal for any of the four sites tested in this paper. Using the four sites described in this paper, comparisons are presented between experimental SWRC results, theoretical results underpinned by fractal theory, and predictions derived from a curve fitting equation based solely on PSD and soil index properties. Lastly, this paper discusses the importance of understanding the unsaturated behaviour of fine-grained soils and some of the challenges associated with aligning current industry practice and advances in research within the field of unsaturated soil mechanics.
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Earthquake-induced landsliding in New Zealand and potential for landslides during earthquakes in Adelaide, South Australia
A study of landsliding caused by historical earthquakes in New Zealand was completed at the end of 1997. That study showed the minimum magnitude for earthquake-induced landsliding (EIL) in N.Z. to be M 5, with significant landsliding at M 6 or greater. The minimum MM intensity for landsliding is MM6 and the most common intensities for landslides are MM7–8. The threshold for liquefaction is MM7 for sand boils and MM8 for lateral spreading. Environmental criteria (landslides, liquefaction) were also defined for the MM Intensity Scale.
In this paper the EIL relationships and MM Intensity criteria are described and then applied in Adelaide. This indicates that an M 6–7 (MM8–9) earthquake in the Adelaide area could cause moderate to large rock falls and slides on high unsupported cuts, river banks, terrace edges and coastal cliffs. Liquefaction damage could also occur in areas of saturated sandy alluvium and estuarine deposits. The historical seismic record, however, suggests that the probability of an M 6 or M 7 earthquake in Adelaide is relatively low; hence the potential risk from earthquake-induced landslides and liquefaction is also likely to be low.
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Engineering Waterproofing Solutions For Underground Civil Infrastructure
Australia is fortunate to have built some of the driest tunnels in the world over the past 20 years with a very strong track record in achieving the highest specification requirement of ‘no damp patches’ over many hundreds of kilometres of tunnel construction. However, this hasn’t always been the case. In fact, early tunnels built in the 1980s and 90s suffered from severe water damage and cost contractors hundreds of millions of dollars in rectification works.
This paper will discuss how the Australian tunneling industry transformed itself by adopting international standards and a strong engineering approach to waterproofing solutions and details. We will review practices from other parts of the world, relevant standards, specifications and experiences using various membrane solutions.
Every tunnel project has its own unique circumstances and requirements which need to be considered during the design phase. Material selection in particular plays a key role in successful outcomes for waterproofing of underground structures. In this context we will review options for station boxes, shafts, caverns and TBM nozzles covering the benefits and limitations of various available materials. There is not a one-size fits all solution when it comes to tunnel waterproofing. We will analyse various projects completed over the past 20 years and the learnings from each of the different applications.
In more detail, the study will reflect on how our industry has managed to create dry cross passages locally, specifically in the most challenging area of terminating the membrane to the TBM segmental lining. We will investigate the engineering design of these terminations and how a robust solution, which is appropriate for underground applications, has been adopted.
With the confidence our industry now has in tunnel waterproofing, we will propose that an Australian Standard be considered with the development of a technical committee. A new local standard would be appropriate for local conditions and be reflective of the skills and knowledge that have been developed over the past two decades.
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Coastal Limestones
The carbonate rocks that have been deposited in the coastal environment of western and southern Australia consist of two main types. Firstly and the most conspicuous are eolianites, which are wind blown limesands that have been cemented in place by calcium carbonate under subaerial conditions. The second group are the beachrocks, which consist of beach sand and gravel cemented in place. As beaches and sand dunes are often contiguous in the coastal environment, so eolianites and beachrocks are associated in present and past coastal environments, and along with shallow marine deposits, tufa, marls, travertines and coral reefs, make up the carbonate rocks that are known collectively as the coastal limestones. These rocks occupy over one quarter of the coastline of Western Australia over some 4000 km. They thus form a major part of the environment where most West Australians live. The limestones underlie the numerous development projects that are transforming the coastal region. The geology and properties of these rocks are however not well documented.
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Are the AS2870 standard designs for residential rafts on reactive clay satisfactory?
The standard raft designs set out in AS2870 are adopted for a significant proportion of residential buildings being built around Melbourne (if not in other Australian cities). Of recent years there has been increasing media coverage relating to the poor performance of footings for residential buildings, particularly in areas underlain by Newer Volcanics basaltic clays. There are many aspects which govern the performance of footings founding on or in reactive clays, and questions regarding the appropriateness of the recommendations in AS2870 are being raised. One such question is whether or not the standard raft designs in AS2870 are satisfactory for reactive clay sites. This paper presents the results of three dimensional finite element soil structure interaction analyses of the performance of standard type waffle and stiffened rafts founded on reactive clay. The performance of the rafts analysed is shown to be unsatisfactory with respect to vertical differential movement and structural capacity when subjected to design characteristic surface movements. Whilst significantly more analyses and research is required, the results of these analyses has significant implications for all of the standard footing designs contained in AS2870 for reactive clay sites. This is particularly relevant given the projected levels of population growth in the coming years in the greater Melbourne area which are underlain by highly reactive basaltic clays.
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Emergency Embankment Stabilisation Works, Pacific Highway, Eungai Creek
The Pacific Highway stretches 900 km from Sydney to Brisbane and has been progressively upgraded and realigned over the last 30 years to reduce travel times and improve safety to road users. The northbound embankment of the highway near Eungai Creek was constructed around 1991 and less than a decade later the highway was upgraded with a second embankment to provide dual carriageway conditions.
Cracking of the northbound pavement occurred as early as 2007. Sealing of the cracks was undertaken, though the cracking continued. In 2017 geotechnical site investigations were undertaken and instrumentation installed in the northbound embankment. Substantial displacement between the concrete pipe sections which formed the culverts beneath the embankment was observed. Monitoring over the subsequent four years indicated relatively minor movement of the toe and crest of the embankment.
Site investigations indicated variable subsurface conditions, with localised zones of firm alluvium within and beyond the embankment footprint, underlain by residual soil and phyllite bedrock. Standpipe piezometers consistently indicated significant artesian groundwater pressures.
A review of the site was undertaken in early 2021 to identify potential deformation and failure mechanisms and provide concept options for the permanent stabilisation of the northbound embankment. Additional investigation, detailed field mapping and survey were undertaken to gain a better understanding of the site and assess whether further deterioration had occurred over recent years. Observed conditions were significantly worse than anticipated such that urgent maintenance and repair works were initiated immediately.
Shortly after completion of the field work, wet weather triggered an embankment failure which required partial closure of the highway. Significant contributors to the failure were the poor condition of the surface drainage which led to saturation and softening of the embankment fill, and artesian groundwater conditions that weakened the foundation soils.
Emergency stabilisation measures were developed for rapid implementation and to allow for the future permanent works. These works comprised the construction of soldier piles along the embankment crest and placement of a rockfill toe berm.
Construction of the emergency stabilisation works has progressed smoothly and allowed the highway to fully reopen and continue to provide its key function as an essential transport artery connecting Australia’s eastern seaboard.
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The consolidation behaviour of alluvial soft clay in Gladstone, Central Queensland
Infrastructure, port facilities and road embankments built on existing soft clay sediments impose various geotechnical challenges. A trial embankment has been constructed at the Wiggins Island Coal Export Terminal (WICET), Gladstone, Queensland to investigate the consolidation behaviour of soft, quaternary alluvial sediments. Large settlement associated with prolonged consolidation time is of particular interest. To predict the magnitude and rate of settlement to allow the design to meet often tight construction schedules, consolidation parameters such as compression and recompression indices, pre-consolidation pressure, coefficients of primary and secondary consolidation need to be reliably estimated. In this paper the consolidation properties of soft clay at WICET were evaluated using three approaches, which are: i) laboratory testing (oedometer); ii) field testing (CPTU with pore pressure dissipation); and iii) back analysis of field monitoring results from an instrumented trial embankment. Derivation of the parameters from the above approaches are discussed, with the results compared and assessed. The benefits of back-analysing instrumentation data to improve the construction programme are also discussed.
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Excavation Induced Ground Movements And Risk Management Strategies
As well as the need to maintain stability, retention systems for excavations in urban environments are required to limit ground movements to mitigate adverse impact to adjacent structures. Tolerable ground movements will depend on the circumstances of the site; in particular the proximity and type of adjacent structures and their foundation type, underground services or tunnels and their current structural condition. It is impractical to limit excavation induced movements to zero even though this may be the wish of the adjacent property and infrastructure owners. Therefore, a site specific risk management strategy is essential for the selection, design and construction of an appropriate retention system for a particular set of site circumstances.
This paper provides a brief overview of excavation performance in different types of ground including a review of measured horizontal movements in deep basement excavations in the Sydney region and a literature study of excavations in soils. The paper then discusses prediction methods including analytical, numerical and empirical techniques, impact on adjacent structures and mitigation measures. Two short case studies are then given to illustrate the adopted risk management strategies. The first case study concerns an excavation adjacent to several existing railway tunnels, for which a risk register together with a monitoring system were used to manage the rail authority’s concerns on potential damage to the tunnel linings. The second case study describes the application of damage assessment that enabled the client to be informed of the risks and the selection of the appropriate excavation and retention method to reduce risks associated with excavation adjacent to heritage listed buildings.