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Shear Strength Of Stockpiled Coking Coal – Existing Data
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 (JCU) from 1973 to 2000 was published in ACARP Report C4057 (Eckersley, 2000).
Eckersley (2022) partly updated that work with SEEP/W transient seepage modelling of a 12 m high coal stockpile constructed at Hay Point in late 1991 for which initial moisture content, pore water pressures at the stockpile base, outflows from subsoil drains and final density and moisture profiles were measured. This provided a good starting point for modelling of moisture movements within production coal stockpiles as required for meaningful slope stability analyses.
The current paper provides an accessible summary of available data from laboratory shear strength testing of coking coal to assist in selection and critical assessment of parameters for slope stability analyses of coal stockpiles. This includes data for saturated coal likely to form the base of a stockpile and currently limited data for unsaturated coal forming the bulk of a stockpile. It then highlights some issues in the selection of parameters for stability analyses of coal stockpiles.
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Correlation between point load strength index and uniaxial compressive strength in Sunshine Coast sandstone
Strength is an important engineering parameter for determining excavatability and load bearing characteristics of rock. Because of the low test cost, it is desirable to identify a multiplier relating the Point Load Test Strength Index (Is(50)) with strength derived using the more expensive Uniaxial Compressive Strength Test. Samples from eight test locations on the Sunshine Coast were tested using both techniques and data were analysed using multiple regression incorporating differences between the eight locations. A multiplier of 17 is observed to produce the most accurate results when inferring UCS from Is(50). This compares with the typical local multiplier of 15. UCS prediction from Is(50) results in substantial errors in some cases and complete reliance on Point Load Strength is not recommended. We recommend that UCS testing should be carried out for each engineering project and multipliers be determined on a site specific basis.
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Sydney Symposium 2022
Reliability-based Design: Advances, Innovation and Experiences
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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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Methods And Approaches For Mitigating The Risk Of Ground Movement Impacts From Tunnelling
Ground movements from excavation works can present project risks with stakeholder engagement, construction approvals, 3rd party claims for damage, time delays and additional cost for mitigation works. The theory of the prediction of ground movements and phased assessment of impacts on structures and infrastructure using simplified approaches has been documented in papers by Rankin (1988), [1] Burland (1995) [2] and several others.
In reality there are numerous complexities which come into the assessment including historical movements, modelling assumptions, quality of asset data, existing condition and individual structural layouts and sensitivities. Many of these variables cannot be modelled, or it is not practical to model. To manage these risks, sets of acceptance criteria have been developed, and where the assessment is within the criteria, the risk of more onerous cracking, deformation or loss of service is considered reasonably low. Similarly, where an assessed impact is higher than a given damage category or acceptance criteria, it indicates the risk is unacceptably high, but the event/failure may not actually occur. On this basis ground movement impact assessments need to be considered as a risk assessment as opposed to an absolute prediction. Often it is the ability to repair any damage which is more important than the magnitude of any cracking itself.
This paper discusses some of the challenges, considerations and approaches that the author has used on major infrastructure projects, along with some of the opportunities and new technologies available for assessment, instrumentation and monitoring and mitigation of the risk of ground movement impacts.
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A review of the experimental studies of the cyclic behaviour of granular materials: Geotechnical and Pavement Engineering
The cyclic behaviour of granular materials has become a critical issue in many civil engineering applications, especially in seismic hazard areas, offshore projects and pavements. Cyclic loading has a detrimental effect on the soil layers under foundations of buildings because it can generate unacceptable deformations and excess pore water pressure in these soil layers. This paper presents the results of research on the behaviour of granular materials under cyclic loading in geotechnical engineering. The cyclic behaviour of granular materials is investigated by using different testing devices as well as various testing conditions. Also, this paper provides a comparison between the response of granular materials in geotechnical aspect under cyclic and monotonic loadings. Moreover, the influence of factors such as drainage conditions, sample preparation method, confining pressure, relative density, frequency, loading type, and stress level on the cyclic behaviour of granular materials was reviewed.
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Hydrogeology of the Botany Basin
This paper seeks to review the current knowledge of the geology and hydrogeology of the Botany Basin, and focuses on how the latter impacts on its geomechanical behaviour. It will consider, briefly, the basin’s encapsulating bedrock foundation rocks, their intersection with the basin fill sediments, the latter’s structure, stratigraphy, lithology, distribution and how these impact on its hydrogeological behaviour. The discussion will then consider the basin’s economic and beneficial value, development within the basin and how this has historically impacted on the basin’s hydrogeology, hydrogeochemistry, water quality and economic value and how development projects need to consider their impact on the basin’s condition and the existing development it supports. Two case studies are presented to illustrate the latter.
At the outset, it is appropriate to define what the term ‘Botany Basin’ constitutes. Rickwood (1998) notes that there “…are those geologists who regard it as a tectonically formed bedrock depression that is the result of post Triassic uplift and warping, and is the smaller part of the larger Sydney Basin” (referencing Roy, 1983), which contrasts with the general view held by hydrogeologists that tend to apply ‘… the name Botany Basin to the topographic depression that is covered by the unconsolidated sediments that form the Botany Sands aquifer’ (referencing Griffin, 1963). Rickwood (1998) further develops the interpretation of the Botany Basin as being “… an easily verifiable bedrock basin … centred on Botany Bay and approximates to the catchment area, but excludes(ing) the extensive drainages of the major rivers entering the basin.” Rickwood then considers the relevance of the Pleistocene basin area and that of the modern basin, settling on the latter as the general basis for outlining the extent of the Botany Basin boundaries.
This paper broadly adopts the general extent of the modern basin as the definition of the Botany Basin, and focuses on the Quaternary sediments contained within that basin and how this aquifer interacts with older bedrock formations which comprise the Pleistocene bedrock paleochannel/paleobasin. The hydrogeological aspects of the bedrock formations, primarily the Hawkesbury Sandstone and Ashfield Shales, are discussed in detail in papers elsewhere in this volume.
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Towards the development of a new guideline for the design of geosynthetic-reinforced column-supported embankments
Deep cement mixed (DCM) columns with geosynthetic reinforcements are used as integrated foundation systems for construction of embankments over soft soils. Several design guidelines are available in the literature for these embankments based on the soil arching and membrane theories. This paper identifies some inconsistencies in applying these design guidelines, especially the shape of the arches formed and their evolution. A two-dimensional numerical model calibrated using a well-established case study confirmed that soil arches formed within the embankment fill are semi-circular or catenary in shape and the size changes during the construction process. Using the same numerical model and the field measurements from the case study, three different design procedures currently available for the design of geosynthetic reinforced-column supported (GRCS) embankments are investigated. All three design methods yielded uneconomical and over conservative predictions for the geosynthetic reinforcements while giving unsafe predictions for DCM columns. Thereby gaps in current design practice are identified and some future research directions are proposed for the development of better design guidelines for these embankments.
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Volume 36, Number 3 — Other
Table of contents, editorial and chairman’s column for Australian Geomechanics, Volume 36, Number 3.