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Methods of investigation and repair of light construction on reactive soil not complying with expectations
Following the procedures of Australian Standard AS2870 does not always give correct, concise, or usable answers to determine why buildings fail. In fact, the answers can be misleading. Throughout the evolution of Australian Standard 2870, stump and bearer construction has been eliminated from reactive sites as has hold down screw piles; neither are in the current edition of Australian Standard 2870. Further, there is a lack of literature on the research that went into Australian Standard 2870 (1986) and why there are now beams for H2D sites (i.e. highly reactive) having an I value (uncracked stiffness) 2.7 that of the 1986 edition. Methods of investigation used today include relative level survey via a water level only, photographic record of cracks and distortion, and geotechnical investigations (bore logs) to determine soil moisture, free swell, and consistency index (Atterbergs Limits). This paper recommends, in necessary cases, that plumbing investigations utilising a newly developed methodology be implemented. This methodology has verified that water is flowing from trenches external to the site in close to 100% of the cases where heave was observed. Three example cases are used as points of discussion, including recycled sites, which have problems of abnormal moisture before construction starts, new construction on new subdivisions, and a case where abnormal moisture conditions happened well after construction. Ultimately the method of repair permanently is hold down screw piles retrofitted, or attempt to control moisture variations after the failure methodology has been corrected.
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Use of dredged materials in a materials offloading facility embankment, Barrow Island, Western Australia
This paper describes aspects of the geotechnical design and construction of a Materials Offloading Facility (MOF) embankment up to 20m high, that consists of material sourced from dredging and plant site development works for the Chevron-operated Gorgon Project – the largest single resource project in Australia’s history. The MOF is located on the eastern side of Barrow Island (BWI), a Class A Nature Reserve. Several significant challenges were faced in sourcing the range of materials required for the MOF. These challenges related to the local geological conditions on BWI and in the near shore environment proposed for the dredging works. Source rock from BWI was used in construction of the initial section of causeway from Town Point to the Pioneer MOF (PMOF) platform, however, this paper only refers to the PMOF and beyond to the MOF Head where the LNG Jetty Abutment structure is located. The materials for these works were sourced from the near shore environment and generally comprised carbonate rich limestone and calcarenite. These dredged materials were considered primarily as rock fill and methods for sourcing and characterisation of the rock fill, selection of parameters, geotechnical analyses and relevant construction details are also discussed in this paper. Design parameters, based on particle size distribution, unconfined compressive strength, particle shape and roughness characteristics were selected and slope stability analyses were undertaken using the limit equilibrium method. Load deformation analyses applied the finite elements coded in the latest readily available geotechnical software. Potential creep and seismic effects were taken into consideration. High strength geotextile reinforcements were used to achieve the required long term embankment stability. Various compaction methods including the relatively new Cofra Dynamic Compaction (CDC) method were adopted at different levels and locations of the embankment and innovative Seismic Surface Wave geophysical methods were combined with Plate Load Testing for verification of the heterogeneous fill materials to ensure the design assumptions would be realised.
The Gorgon Project is operated by an Australian subsidiary of Chevron (47.3 percent interest), in joint venture with the Australian subsidiaries of ExxonMobil (25 percent), Shell (25 percent), Osaka Gas (1.25 percent), Tokyo Gas (1 percent) and Chubu Electric Power (0.417 percent).
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Proceedings of the 2016 Sydney Chapter Symposium
This document contains papers for the 20th annual symposium organised by the Sydney Chapter of the Australian Geomechanics Society. It is hoped that the symposium will keep practicing geotechnical engineers, engineering geologists, and other engineering professionals informed of recent developments in this field. It also recognises the need to gather together the experience of those practicing throughout Australia and to allow transfer of knowledge and sharing of their experiences.
These symposia continue to be one of the best forms for bringing together the key stakeholders of the Australian geological and geotechnical community. The main objective of the symposium, held on 11 November 2016, is to advance the knowledge in design and construction towards more cost effective ground improvement techniques in urban infrastructure environment.
Contributors include academics, practicing consultants, designers, suppliers and contractors. The papers present novel design and construction technologies for the performance monitoring of various ground improvement techniques applicable to soft soil and unstable rocks as well as new research results and case histories on construction.
This symposium is the cooperative effort of many authors and qualified reviewers. The editors and organising committee wish to thank the authors, who have generously contributed their time to prepare the various papers and the colleagues of the authors, who have assisted with time, secretarial, drafting and other facilities. Appreciation is also extended to our sponsors for their support. Without them the Symposium would not be possibly the best ongoing forum for the Australian Geomechanics and groundwater community.
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Digital Twin For Underground Stations: Improving Decision Making For Construction Lifecycle
Challenges in the extraction and use of earth resources and spaces are encountered given a growing worldwide population, rising infrastructures development, and widespread climate change. In Australia, mining and construction are two major bases for economic growth while both being traditional hazardous and heavy industries. A nation-wide infrastructure upgrade featuring large-scale underground development is underway, the geological uncertainties and localisation difficulties of already laid infrastructure are associated with challenges not seen in building construction. A safer and competent subterranean transport solution is yet proposed in the context of sustainable developments. In light of this, geotechnical analysis as a fundamental subject for developing and maintaining safe and sustainable use of underground space has huge potential to be undertaken more intuitively considering the advancements in information management and visualisation. The PhD work examines the state-of-the-art applications, limitations and future opportunities of Building Information Modelling (BIM) and other computational techniques in the digitisation of tunnelling and underground construction. The visualisation and interoperability facilitated by data-driven processes are especially important to underground construction that engages interdisciplinary and multi-environment interaction.
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Shear Strength Of Stockpiled Coking Coal – Insights From Stability Analysis Of Two Instrumented Stockpiles
ACARP Report C4057 (Eckersley, 2000) describes flowslides and other stability issues in stockpiles of coking (metallurgical) coal at Australian coal operations and export terminals, and summarizes 1973 to 2000 research at James Cook University (JCU). Eckersley (2022) partly updated that work with SEEP/W transient seepage modelling of a 12m high coal stockpile constructed at Hay Point in late 1991.
Eckersley (2023) summarized available laboratory strength data for saturated and unsaturated coking coal to assist in selection and critical assessment of parameters for slope stability analyses of coal stockpiles. The current paper explores application of this data to stability analyses of two instrumented experimental stockpiles constructed at Hay Point, one of which collapsed suddenly and completely by flowsliding after extensive wetting. The stability analysis results tentatively confirm that the parameters and approach proposed are reasonable where stockpiles are subject to potential liquefaction-induced collapse.
Significant questions raised by Eckersley (2023) regarding how the coking coal strength data should be applied are considered in the context of the stability analyses. The analyses tentatively confirm that effective strength parameters for saturated coal derived from peak deviator stress in isotropically consolidated, undrained (CIU), strain controlled triaxial tests are reasonable. For loose saturated coal these are at low strains and substantially less than critical state values. However, for unsaturated coal forming the bulk of a stockpile, unsaturated strength and apparent cohesion should be assessed from the effective friction angle at critical state and not the value mobilized at low strains. Use of total stress parameters derived from testing unsaturated coal may over-estimate factor of safety.
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Geotechnical site investigation in energetic nearshore zones: opportunities and challenges
Coastal erosion and scour around structures in the nearshore zone represent major societal challenges with regard to coastline conservation, the protection of coastal communities and eco-systems, as well as the development of coastal structures or renewable energy projects. Despite rapidly advancing sediment erosion, scour and morphodynamics prediction tools, the models still struggle to correctly simulate the impact of severe storm events and storm event clusters, particularly regarding long-term projections considering sea level rise and climate change. Scour prediction models still struggle to accurately predict the depth and extent of the scour around a structure, and often rely on significant overpredictions which impact the cost-efficiency of the structural foundation design. A review of common erosion and scour prediction models reveals that particularly sediment characteristics appear underrepresented. This results from challenges to derive this information in the field. Areas of active sediment remobilization processes, such as the nearshore zone, are characterized by energetic hydrodynamics (waves, tides and currents), and morphodynamics (migrating bars, etc.) representing challenges and risks to people, vessels and instrumentation. Most geotechnical field instrumentation to-date are not designed or suitable for measurements in such conditions, and new devices are needed to fill this gap. This paper presents results (i) using a portable free fall penetrometer of projectile-like shape to investigate in situ characteristics and stratification of sediment surface sediments in the nearshore zone under hydrodynamic forcing, and (ii) preliminary data using embedded pressure sensors to investigate the pore pressure response to irregular wave forcing in the nearshore zone and its potential impact on sediment erosion. The devices proved to be suitable for the deployment in energetic nearshore conditions. The data emphasize the potential regarding deriving novel information about in situ sediment characteristics, such as changes in sediment strength under the active sediment dynamics, as well as an increase of erodibility through the development of excess pore pressures on different time scales. However, the data also reveal challenges related to calibration of the instrumentation and data processing, particularly with limited additional information about the sediment.
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Design And Construction Of Roma Street Station Cavern, Cross River Rail, Brisbane
The new Roma Street underground railway station in Brisbane is being constructed as part of Cross River Rail’s Tunnel, Stations and Development (TSD) package. The joint venture of CPB Contractors, BAM International Australia, Ghella and UGL (CBGU JV) is building the 5.9km long twin tunnels from the Southern Tunnel Portal near Dutton Park station, beneath the Brisbane River and CBD to the Northern Tunnel Portal in Spring Hill. The Cross River Rail project includes excavation and construction of four new underground stations.
Roma Street station comprises a 280m long cavern, five smaller connecting tunnels (adits) and three shafts. The station cavern has an excavated span of up to 24.4m with approximately 15m rock cover. It has been excavated within the Neranleigh-Fernvale Group (NFG) rock mass, which comprises weakly metamorphosed sandstone (meta-greywacke and arenite), phyllite and subordinate quartzite and meta-basalt. The station lies within the regional Normanby Fault Zone, characterised by a major fault up to 20m wide comprising a combination of intact rock, rock breccia and clay gouge. The fault zone encountered during the station cavern excavation required heavier primary support and localised foundation treatment.
The initial primary (temporary) support of the cavern and adits comprised rock bolts, cable bolts and a thin synthetic fibre-reinforced shotcrete lining. In some areas a passive shotcrete arch lining was required. Overlying piled footings from an existing busway overpass structure were within a metre of the adits’ excavated profile which necessitated a complex load transfer structure at the surface and verification of pile toe levels during tunnel construction.
The cavern permanent lining typically comprises steel fibre-reinforced concrete in the crown, bar reinforced concrete for the sidewalls, and bar and steel fibre-reinforced concrete invert slabs. Bar reinforcement is used in the cavern crown where it intersects the adits. Ground loads for the permanent structure had to consider the influence of future developments.
This paper presents some of the challenges of the primary support and permanent lining design of the station cavern and adits. It summarises the as-encountered ground conditions, aspects of the primary support and permanent lining design that were geotechnically challenging and the solutions developed to meet the project requirements.
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Footing design for residential type structures in arid climates
The parameters required for the design of footings on expansive (or reactive) soil by AS2870-1996 for arid regions of Australia are derived theoretically from established relationships based on experiences in the more temperate climates. Two critical parameters required for a footing design by AS 2870-1996 are the surface soil suction change (∆us) and the depth of the design soil suction change (Hs), and current recommendations for arid climates have a range ∆us = 1.2pF to 1.8pF, and Hs=3.7 m to 6.0 m. Using the results of solutions of the diffusion equation, with values for the diffusion coefficient for a soil profile in an arid climate that are extrapolated from the established relationships between the Thornthwaite Moisture Index, the annual cycle of wet/dry months and Hs in the more temperate climates, it was found that for an arid climate, ∆us=1.8pF and Hs=2.5 m. This finding was supported by a case history of a building in the Jackson oil-field, south west Queensland that had been distorted by the effects of an expansive soil profile. Three worked examples, using ∆us=1.8pF and Hs=2.5 m for the design of a footing for a residential type building on an expansive soil in an arid area, are given.
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Characterisation of municipal solid waste materials for the purpose of engineering design in transport infrastructure project
Space restriction especially in the urban area has contributed to the reuse of landfill area, where Municipal Solid Waste (MSW) is disposed, for the purpose of infrastructure development. This type of development presents some significant challenges in the engineering design due to high variability of MSW properties and the uncertainty in relation to the application of conventional geotechnical engineering principle for the engineering design involving MSW materials. MSW materials are highly variable not only in different landfill sites, but they also are likely to vary over the distance and depths within a landfill site. In addition, the engineering properties of MSW materials are influenced by a number of factors including the landfill age, constituents of landfill, placement method and the leachate recirculation. This variability along with a risk associated with the biological and chemical hazards arising from the direct exposure to the waste materials and toxic gas pose limitations in conventional (a) geotechnical site investigation and (b) laboratory testing of MSW. Therefore, characterisation of MSW for the engineering design needs to be carried out based on limited site specific information and published data. This paper presents a typical geotechnical investigation and characterisation of waste materials for the engineering design of a transport infrastructure considering the aforementioned limitations. A case study involving a proposed transport infrastructure over an active landfill site in NSW has been selected. A Geotechnical Site Investigation (SI) involving a sonic borehole drilling has been carried out with a primary objective of obtaining continuous samples for the observation of waste materials as opposed to the in-situ testing and drilling with poor recovery. In addition, test pit excavation and geophysical investigation have been carried out to gather more information to develop the geotechnical model. Various MSW materials recovered in the boreholes and test pits were thoroughly assessed on site during the SI to obtain the MSW composition including the proportion of each type of waste material using the method outlined in Landva and Clark (1990). This observation was then compared against the results of geophysical investigation. By using the outcome of SI, previous geotechnical investigation and settlement monitoring conducted about 30 years ago within the subject area and extensive published data on MSW properties including the Waste Compressibility Index, a comprehensive guide has been prepared to develop the design parameters for geotechnical design of the proposed rail embankment. This guide will be a useful tool for practicing engineers to develop geotechnical design parameters of landfill materials.
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The weighted plasticity index in road design and construction
The commonly used Plasticity Index (PI) test disposes the material retained on the 425 micron sieve, thus is not representative of the whole sample. In Australia, residual soils are very common, with a high granular content in “clayey” soils. Thus a significant portion of the sample is discarded for the PI (only) test. The weighted plasticity index (WPI) accounts for the portion used in the PI test and this is important for classification of residual soils. The background and historical development of the WPI is presented with its relationships, applications and limitations. Changes in testing Standards affects the correlations expected with the original WPI classification.