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Introduction to the ‘CGSE Special Issue’ of Australian Geomechanics
The Newcastle Chapter of the Australian Geomechanics Society is pleased to dedicate its themed issue of Australian Geomechanics to the activities of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering (CGSE), which combines three of Australia’s leading geotechnical research groups: the Centre for Geotechnical and Materials Modelling at The University of Newcastle, the Centre for Offshore Foundation Systems at The University of Western Australia, and the Centre for Geotechnics and Railway Engineering at the University of Wollongong. With a forecast investment of over 250 billion dollars in Australia’s energy and transport infrastructure over the next five years, there is an unprecedented need to design and build this infrastructure as cheaply and safely as possible. In light of the size of investment involved, even small percentage savings resulting from scientific research will lead to huge returns in absolute dollar terms. Through advanced laboratory testing, physical modelling, full-scale field testing and cutting-edge computational simulations, the CGSE is providing engineers with new science-based tools for designing safer and cheaper energy and transport infrastructure such as roads, railways, port facilities, tunnels, dams, pipelines, mining operations and offshore oil and gas facilities. The CGSE has four geotechnical science themes, each of which is linked to advanced computational modelling, state-of-the-art physical modelling and laboratory testing, and engineering applications: Geomaterial Science, Multiphysics Modelling, Moving Boundary Problems and Georisk.
The collection of articles in this issue highlights the complementary skills and facilities brought together from each of the nodes and the innovative research produced by the CGSE. The first of two articles that summarise recent developments in the testing equipment and physical modelling techniques available within the CGSE is the contribution by Cassidy et al. (2014), which describes the new National Geotechnical Centrifuge Facility, a recently established mobile in situ testing laboratory, and the new national facility for the cyclic testing of high-speed rail. The second paper by White et al. (2014) describes the recirculating flumes, or O-tubes, that allow for simulation of ocean-structure seabed interactions in offshore applications and, in particular, the stability of pipelines on mobile seabeds.
A series of papers covers various aspects of the work being conducted in conjunction with soft soils, for which the CGSE has developed Australia’s first National Soft Soil Field Testing Facility (NFTF) in Ballina, NSW. These articles include an overview of the site and the in situ testing programme (Kelly et al., 2014), a discussion of current and future work on sampling and laboratory testing on Ballina clay (Pineda et al., 2014), an investigation of spatial variability based on field tests completed at the NFTF (Li et al., 2014), and a study aimed at investigating the effects of strain rate and softening in vane shear testing (Ansari et al., 2014). A fifth article on soft soil focuses on developments in the understanding of vacuum preloading as a means of accelerating consolidation (Indraratna et al., 2014a).
Three articles describe past, present, and future research on onshore and offshore foundations. Gaudin et al. (2014) give a comprehensive review of the analytical, numerical, and physical modelling techniques developed within the CGSE to understand and predict the performance of offshore anchoring systems. Hambleton et al. (2014a) present findings within a new focus area on modelling the installation process for helical anchors and piles. Gourvenec and Feng (2014) describe the innovative design methodologies developed to economise offshore foundations through analysis of the capacity, foundation configuration, soil characteristics, and the mode of operation.
In the area of transportation geotechnics, two contributions focus on the performance of railway foundations. The study by Tennakoon et al. (2014) considers the influence of contamination of ballast on its drainage and shear strength characteristics, and Indraratna et al. (2014b) review laboratory and field testing on shock mats which can be used to reduce ballast degradation and improve stability of railroad tracks. A third study on transportation geotechnics (Heitor et al., 2014) examines cost-effective techniques for assessing the adequacy of compaction in projects with high fills covering large areas, where conventional quality control methods can be prohibitively expensive.
Two articles illustrate the challenges associated with problems involving ultra-large deformations. O’Loughlin et al. (2014) provide an overview of the centrifuge modelling, field testing, and numerical modelling being completed to understand and predict the behaviour of free falling projectiles such as torpedo anchors and penetrometers. Hambleton et al. (2014b) highlight current and future research initiatives within the CGSE on modelling the progressive displacement of soil in ploughing and cutting processes, which lie at the heart of earthmoving operations occurring at numerous scales in various environments.
Three papers showcase advances in the numerical and analytical tools developed within the CGSE. Kardani et al. (2014) demonstrate the improved computational performance that can be achieved in the numerical analysis of coupled consolidation problems through the use of high-order elements in adaptive finite element methods. Vinod et al. (2014) present a technique based on the discrete element method (DEM) for investigating the mechanical behaviour of sand containing methane hydrate. Huang et al. (2014) discuss the means by which Bayesian statistical methods can be used for improved prediction of performance geotechnical projects, considering two examples involving load testing of piles and settlement prediction from field monitoring data.
Each of the papers in this edition was anonymously peer-reviewed, and the Newcastle Chapter extends its sincerest gratitude to each of the reviewers.
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Challenges to Digital Transformation in Geotechnical Engineering
The application of digital data and technologies in geotechnical engineering is not new; however, the use is sporadic and inconsistent among geotechnical engineering specialists and firms across the world. Further, this use is often limited to specific areas such as processing of field data during ground investigations and detailed numerical analyses of complicated foundation systems during design. There is a general lack of interoperability among the various digital tools and systems, which is inhibiting efficiency that could have been achieved otherwise using compliant platforms which can readily transfer data and models. This paper examines by way of examples where digital data and technologies are being used to increase efficiency in design and construction and enhance collaboration on construction projects. The paper explores the current state of the art and future potential opportunity to automate the whole geotechnical design process of capturing field data, generation of ground models, analyses and design, and visualisation of final solutions without the need for manual data entry at any of the intermediate stages. The level and stages where human input would continue to be required in geotechnical engineering are also reviewed, given the level of empiricism we still adopt due to significant gaps in our understanding of the variability of natural materials, behaviour of ground under loading and due to its complex interaction with other man-made materials and structures. In addition, a view is taken of the market driven barriers that might be limiting the efficiency of the geotechnical industry and the society in general, which could gain from the ongoing digital transformation.
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2021 Tasmania International Symposium
Offshore Geotechnical Engineering: Challenges in Wind, Wave and Tidal Renewable Energy
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Shortland Esplanade, South Newcastle Beach, Australia: A case study in rockfall risk management
Shortland Esplanade at South Newcastle Beach traverses a stunning scenic location, at the base of an imposing coastal cliff line and defined by a sea wall that adjoins the Pacific Ocean. The cliff line and the sea wall comprise constraints that dictate the geometry, operation and management requirements of the esplanade alignment.
The subject section of Shortland Esplanade has had a history of rockfall activity from the overlying coastal cliffs, one such episode of which prompted Newcastle City Council to close the esplanade to protect the public from ongoing rockfall hazards. GHD Geotechnics were subsequently engaged to provide the following services:
- Identification of rockfall risk mitigation options
- Quantification of rockfall risk (QRA) before and after mitigation
- Design and supervision of Council’s preferred mitigation strategy.
These aspects of this notable case study are described herein.
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Monitoring of Sprayed Concrete Lined Tunnels Using Fibre Bragg Grating Sensors
This paper outlines the use of Monitor Optics Systems’ (MOS) Fibre Bragg Grating (FBG) sensor cables for convergence monitoring in tunnels made from sprayed concrete lining (SCL). The Crossrail project is currently installing the new Elizabeth line into the London rail network, and at Farringdon Station, the line will connect to both the London Underground and the Thameslink lines. Due to several of the new tunnels being in close proximity, as well as existing infrastructure and challenging geotechnical conditions, the decision was made to monitor the critical “RTE2” tunnel to ensure it was performing as designed. Pressure sensors and survey prisms were initially selected to monitor the tunnel’s critical locations. However, as pressure sensors had a reputation for unreliable results due to difficulties with their installation, an additional method was sought out to validate the pressure and surveyed results. Following their successful use in a tunnel at Bond Street Station, MOS sensor cables were selected to monitor the tunnel in conjunction with the pressure sensors and survey prisms.
MOS sensor cables that incorporate a nylon coating are designed to survive direct embedment into the SCL of a tunnel and can provide real time monitoring of the lining immediately after embedment. Sensor cables with five FBGs were installed at two locations in the RTE2 tunnel, along with corresponding temperature sensor cables. The FBGs were monitored using an optical interrogator located outside of the installation area through the use of fibre optic signal cables. Data was available for visualisation and manipulation through the MOS web hosting site DaMiNs.
FBGs, survey prisms, and pressure sensors were located at the same locations, and the FBG results generally showed good agreement with the surveyed results. The majority of the pressure sensors were unable to capture reliable results but were also in good agreement with the FBG results where reliable data was captured. The monitoring results validated the tunnel design and allowed additional tunnel construction to continue without additional unnecessary concrete linings.
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GIS-based back analysis of riverbank instability in the Lower River Murray
Over the last 4 years or so, unprecedented low river levels, combined with current loading conditions, have adversely contributed to more than 137 riverbank collapse-related incidents and a long term metastable condition along the Lower River Murray, which have recently been considered as the dominating factors inducing bank collapse. With high resolution aerial photographs and digital elevation models (DEMs), this study has established the riverbank geometry prior to collapse of 26 2-dimensional cross section models. Based on government inventories, the collapsed riverbank sections were identified and vectorized using visual interpretation under ArcGIS. In order to obtain appropriate soil parameters for the study area, 5 back analytical models have been conducted at collapsed riverbank sections adjacent to Long Island Marina, Murray Bridge, South Australia. The slope stability analysis software SVSlope was employed in the back-analysis with soil data obtained from two nearby site investigations. Factors of safety were calculated to examine the potential for riverbank collapse with respect to varying river levels. The results indicate that, when the river levels return to 0 to 0.5 m AHD, a portion of the riverbank is close to collapse, whereas a large proportion of the banks remain quasi stable. A raised and maintained high river level will improve the stability but to a limited extent. Several remedial works may need to be conducted when the river level is about to decrease.
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Making Earth Materials Talk
How Earth materials are used as evidence in crime investigations
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An Emperical Model To Correlate Rock Mass Classification And Hydraulic Conductivity, Geotechnical Engineering Data Acquisition And Reduction Perspective
This paper presents an empirical model for estimating rock mass hydraulic conductivity of fractured Hawkesbury Sandstone in the Sydney basin. The hydraulic conductivity of a fractured crystalline rock mass can be a critical factor in tunnelling projects and dewatering designs. The Lugeon test (commonly known as the “packer test”) is a common test used to estimate the in-situ permeability of a rock mass.
The Packer test is carried out over a specific length (typically 3-6 m) within a borehole to reduce the range of variation of the affecting parameters. To construct a detailed profile of hydraulic conductivity through the rock mass a relatively large number of Packer tests are often required which can be costly and time consuming.
The new rock mass classification system called the “HC system” was proposed by Hsu et al. (2011). The HC-system assists with the hydraulic modelling of a rock mass and is based on 4 parameters which can be readily assessed from borehole logs and borehole Televiewer data, namely Rock Quality Designation (RQD), Depth Index (DI), Gouge Content Designation (GCD) and Lithology Permeability Index (LPI). A modified new rock mass classification system called the “HC-system” or HC model has been specifically developed for Hawkesbury Sandstone in the Sydney basin.
Regression analysis was conducted to assess the correlation between the calculated HC value (using the HC model) and the corresponding hydraulic conductivity from the in-situ packer tests.
To confirm the feasibility of the proposed empirical HC model, the model was subsequently used to estimate the hydraulic conductivity of similar Hawkesbury Sandstone boreholes from a range of projects that also have corresponding Packer test data for comparison.
This empirical HC model may assist with two important hydrogeological applications. The first application is to estimate hydraulic conductivity of fractured sandstone of similar geological set up based on HC-values. By using this approach, hydraulic conductivity data in a given site can be estimated from borehole data, which increases the reliability and confidence of the packer testing. Secondly, for in-situ aquifer tests the HC-system is a valuable new rock mass classification system for estimating the degree of permeability of a borehole. The results obtained confirm the validity and flexibility of the empirical approach to handle cases of onshore and offshore data sets, in relation to data acquisition and data reduction (optimisation).
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Foundation Investigation In Weak Slaking Rock, Darwin, Australia
Most of the Darwin CBD is underlain by a Mesozoic rock locally termed porcellanite. Much of this is a silcrete which can be up to 8 m thick and is typically high to very high strength. Many of Darwin’s buildings are supported on shallow footings founded on porcellanite and there is little available geotechnical information of relevance to foundation design in the weathered Proterozoic phyllite underlying the porcellanite.
This paper describes a foundation investigation and design for a 34 storey building with sunken lift core in Darwin which, when complete will be the tallest in that city. Preliminary footing design by others was based on the precedent of shallow footings supported in the porcellanite. A preliminary geotechnical investigation (by others) comprising boreholes to a depth of about 15 m, indicated that a significant thickness of porcellanite underlies only part of the site and that footings would need to be supported on older deeply weathered phyllite or a thin layer of porcellanite overlying phyllite. Based on low soil stiffness properties estimated mainly on the basis of low SPT ‘N’ values large diameter deep bored piles were proposed as a means of reducing differential settlement.
To further investigate the proposed footing solution options, a supplementary geotechnical investigation was undertaken to obtain estimates of the engineering properties of the phyllite. Diamond core drilling with pressuremeter testing was undertaken. However core recovery was poor and the results of the pressuremeter testing were affected by the slaking of the phyllite. The stiffness of the phyllite was subsequently estimated using dynamic load testing of precast concrete piles placed into pre-drilled sockets at select depths. Analyses using the estimated stiffness properties of the phyllite suggested that differential settlements could be kept within acceptable limits using a shallow footing solution, which was subsequently adopted. The footing system has since been constructed and construction is near completion. Settlement monitoring indicates settlements less than design predictions.