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Mineralogy Of Sydney Building Sandstones In Relation To Geotechnical Properties – 1: Relation Of Quantitative X- Ray Diffraction Data To Other Chemical And Petrographic Indicators
The SIROQUANT processing system has been used to determine, on a quantitative basis, the percentages of the clay and non-clay minerals from X-ray powder diffraction data, for a series of sandstone samples from materials previously used as dimension stone for repair or extension to heritage buildings in the Sydney area. Evaluation of the results shows them to be consistent with a number of other techniques used to evaluate rock composition, including petrographic and chemical analysis, and with separate determination of clay mineralogy by oriented-aggregate X-ray diffraction methods. The cation exchange capacity of selected samples was also evaluated, using a modification of the standard technique for soil studies, and found to be related to the total clay mineral content as evaluated by SIROQUANT, as well, to a lesser extent as the relative proportions of illite and interstratified illite/smectite in the rock samples.
Use of X-ray powder diffraction as a quantitative tool provides a basis for rapid and reliable evaluation of rock mineralogy, which in turn exerts a fundamental control on rock behaviour under different geotechnical conditions. These relationships will be discussed further in the second paper of the present series.
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Proceedings of the 2017 Sydney Chapter Symposium
This document contains papers for the 21st 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 10 November 2017, is to present overview of current transport infrastructure challenges, state-of-the-art practices, innovative technologies, new research results and case histories demonstrating applications of advanced techniques and cost-effective approaches in the construction and design of transport infrastructure.
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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Internal Compression Of Fill Material Originating From Bringelly Shale
A rule of thumb handed down from senior to junior geotechnical engineers in Australia is that internal compression of embankment fill is 0.1% of embankment height and it has been widely used in performance specifications for major infrastructure projects around Australia. It is not clear where this rule of thumb originated from or on what basis it was developed. In Western Sydney this rule of thumb has been adequate for many years because the scale of earthworks in terms of fill thickness has been relatively minor. Large scale earthworks have started to occur over the past decade or so as more significant road and rail development has occurred. Recent experience with higher fills constructed in Western Sydney shows that internal compression strain rate can be greater than 0.1% per log cycle of time. Embankments to about 10 m height on a rail infrastructure projects on Western Sydney were constructed from Bringelly Shale. The fill materials and compaction were compliant with the relevant engineering standards. Comparison of topographic survey about 5 years after construction with design profiles indicated that they had settled between 0.05 and 0.25 m, subject to construction tolerances, and the internal compression strain rate varied between 0.5% and 6.3% per log cycle of time, adopting 1 year as the starting time of post construction settlement. Anecdotal evidence from road embankments of up to 14 m have identified similar magnitudes of settlement response from fill formed of the same Bringelly Shale materials. These values are much higher than the rule of thumb of 0.1% per log cycle of time. Though Bringelly Shale-based fill material has shown such a significant settlement issue, to the authors knowledge, there are no references found in the technical literature that provides some guidance on assessing the internal compression of Bringelly Shale based fill material. Therefore, a series of laboratory tests have been conducted to understand the settlement behaviour of compacted Bringelly Shale. Compaction tests, particle size distribution, Atterberg limits, and small and large-scale compression tests of compacted fill material have been conducted. This paper summarises some of the findings of the laboratory tests and authors’ view on the performance of Bringelly Shale fill material and future studies.
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Separating influences of yield stress ratio (YSR) and partial drainage on piezocone response
Calculation of failure loads is typically a part of most geotechnical designs. For evaluation of the potential for failure, soil behaviour is essentially governed by the initial yield stress ratio (state), the stress level at failure, and the degree of consolidation during loading. These facets of behaviour will not only influence geotechnical design, but also strongly influence the soil response measured during a cone penetration test (CPT) with pore pressure measurements, or piezocone penetration test (CPTU). This study evaluates a method to separate the influence of yield stress ratio (YSR) from partial drainage during a CPTU, with particular application to soil classification by piezocone. Increases in YSR and degree of consolidation during loading tend to result in an increase in normalized cone tip resistance (Q=qcnet/σ’v0) and decrease in pore pressure parameter (Bq=∆u2/qcnet), which are typically used for soil classification by piezocone. Using theoretical studies, centrifuge experiments, field experiments, and databases of CPTU measurements, this study illustrates that for many cases the influence of YSR and partial consolidation have opposite effects when plotting data as Q against ∆u2/σ’v0 (=Bq⋅Q). Therefore, charts of Q plotted against ∆u2/σ’v0 are more useful for evaluation of soil type than conventional plots of Q against Bq.
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Load Settlement Performance Of Two Towers
Redevelopment of the south bank of the Yarra River in Melbourne comprises eight multi level residential towers and a number of other related structures. Two of the towers experienced problems during installation of their piled foundations that might have led to increased settlements if left unremediated. This paper describes the foundation problems that arose and the methods used to assess the potential settlement of the towers. On the basis of these estimates additional piling works were required for one of the towers. The foundations for the other tower were considered to be satisfactory. Settlement monitoring carried out during construction of the towers showed excellent agreement with settlement estimates and justified the decisions made.
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Hydrogeological properties of the Hawkesbury Sandstone in the Sydney Region
Geotechnical and hydrogeological data obtained from investigations for the design of tunnels in Sydney have created a large database that describes the hydrogeological properties of the Sydney Hawkesbury Sandstone, providing an insight into its hydraulic behaviour. Investigations for the Epping to Chatswood Rail Line and another tunnel project in Sydney included drilling of over 150 boreholes and execution of over 450 packer (water pressure) tests within these boreholes. For the Epping to Chatswood Rail Line, a 48-hour pumping test was conducted at two separate locations and acoustic borehole imaging was conducted in 20 boreholes to provide information on subsurface defect characteristics, essential to understanding hydraulic behaviour. This paper presents the results of a statistical analysis of packer test results and borehole imaging data, a comparison to pumping test results, and compares measured groundwater inflow rates from the tunnels with estimates from numerical modelling. Data analyses show the depth-dependence of the hydraulic conductivity of the Hawkesbury Sandstone, show a relationship between hydraulic conductivity and defect distribution, and demonstrate the requirement to address scale effects when using packer test results to assess groundwater inflow to underground excavations.
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Geotechnical aspects of earthquake hazard assessment for Brisbane
An effective method was needed to resolve earthquake hazard at the city-scale during the development of an earthquake risk assessment for Brisbane. While an assessment of regional seismicity is a fundamental input to the process, it can only provide a broad idea of earthquake hazard. Two of the major determinants in magnifying local earthquake shaking above regional levels are (i) the presence of significant thickness of weak foundation sediments with high void ratios and, (ii) the effects of ridge-tops and steep slopes. Soft, Recent sediments, deposited in low-lying areas around the Brisbane River and Moreton Bay coastal plain will tend to magnify the effects of earthquakes. Steep, narrow ridges are a common feature in the central and western districts of the city. Recent acquisition by Brisbane City Council (BCC) of a high-resolution digital elevation model (DEM) of the city area and a broader range of sub-surface geotechnical information has enabled an enhancement of earlier hazard analyses. The geotechnical borehole dataset available to BCC, although now broader, is nevertheless limited as a much larger database remains for potential exploitation. The new DEM enabled refinement of geological boundaries to match the scale of assets at risk, and provided additional visual clues as to subsurface conditions and indications of sediment thickness, as well as providing accurate delineation of slope and slope change. The existing coverage of geological mapping is comprehensive but mapping is at a coarse scale compared to that at which city assets are described. Available microtremor recordings are available but too restricted to be sufficiently representative for a whole-of-city assessment. Taken together, however, the DEM, available geotechnical borehole data, geological mapping and microtremor recordings are able to provide a reasonable delineation of potential variations in the magnitude of earthquake shaking, within the constraints of the given regional seismic setting. While such studies provide an assessment of hazard, further combination with information on the demographic setting, vulnerability and assets at risk through risk-GIS was necessary to quantify risk. The study shows that while nowhere is entirely immune to earthquake effects, the chance of an earthquake causing significant damage in Brisbane city is unlikely. The earthquake hazard to Brisbane is low by global standards. Less than ten minor earthquakes have been felt in the city since its founding, some 180 years ago. The largest of these, the Richter magnitude ML 4.4 Mt Glorious earthquake of 1960 caused minor damage but was felt throughout Brisbane with intensities as high as Modified Mercalli intensity MM IV. A maximum Richter magnitude of ML 6.5 is theoretically possible within the region which includes Brisbane. However, concentrations of vulnerable populations, housing and infrastructure largely lie outside of the zones of highest earthquake hazard, reducing the overall risk to Brisbane considerably.
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A Numerical Parametric Study Of The Effectiveness Of The 4-Sided Impact Roller
Rolling dynamic compaction (RDC) is a specific type of dynamic compaction, which involves towing a heavy non-circular module at a relatively constant speed. This paper investigates the effects of module mass, operating speed and varying ground conditions on the effectiveness of the 4-sided impact roller using a developed finite element method (FEM)-discrete element method (DEM) model. Numerical results were analysed from four aspects, namely the energy imparted to the ground, soil velocity vectors, module imprint lengths and soil displacements at different depths. It is found that, a heavier module mass induces greater ground improvement in terms of both energy delivered to the soil per impact and the magnitude of soil displacements. The energy imparted to the underlying soil by the module increases with greater operating speed. The rotational dynamics of the module also change with increasing operating speed, whereby the impacts are delivered by the faces of the module at typical operating speeds; however, at faster speeds the impacts are delivered towards the corners of the module and the behaviour is less reproducible. The modelling showed that soil with a higher initial Young’s modulus and a higher internal angle of friction decreases the magnitude of soil displacements, which confirms that the impact roller is less able to significantly improve soils that are stiff or have a high initial shear strength.
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On best practices for trackbed design
This paper reviews the best practices of trackbed design for railway projects. Various existing methods have been studied and recommendations for more economical design are provided. The analytical/empirical methods from various standards such as UIC, AREMA, British Rail, and Australian standards, as well as other commonly used methods such as Raymond and Li-Selig are compared based on a typical track embankment cross section. The outcome was then evaluated against 2D and 3D numerical models. Incorporating numerical methods is shown to render considerable reductions in the required prepared subgrade/structural fill materials and allow for assessment of long-term design issues, such as subgrade shear failure due to excessive plastic deformations.
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Working platforms -To BRE or not to BRE is the question
The Building Research Establishment (BRE) produced a practice guide for working platforms for tracked plant, which has become a “standard” in the industry in the absence of any other widely published simple design method. The BRE design method does not apply for thick platforms or for soft subgrades, but continues to be used in those applications in the absence of an alternative document. A case study is discussed which applies the BRE in such a situation, but then compares with alternative methods to assess the required working platform. Additionally a stochastic approach is used with the BRE method, given its sensitivity to the material strength parameters input, to provide a risk understanding rather than a factor of safety approach which does not define the risk explicitly. The derivation of the parameter inputs is discussed to show how assumed values for preliminary design and measured values produce different design platform thickness. Given the consequences of a failure, a construction control proof roll testing was used with deflection criteria. The derivation of this criterion is presented.