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Geotechnical Parameters Of Sydney Sandstone And Shale
The classification system for Sydney sandstone and shales, through the Australian Geomechanics Society (Pells et al, 1978; Pells, Mostyn and Walker, 1998) was intended to assist in the design of foundations on rock in the Sydney area. The five class system has proved to be a good tool for communicating rock mass quality for other geotechnical projects such as tunnels and deep basement excavations. However, the classification system is not a design tool for works other than foundations on rock. Tunnels, slopes, deep basements and retaining walls should be designed using normal methods of applied mechanics. However, such methods, whether hand stability calculations or complex analyses using programs such as UDEC, require engineering parameters covering strength and deformation characteristics. In some instances, such as rock substance strength and modulus, the parameters may be measured by laboratory testing. However, when it comes to rock mass parameters use has to be made of parameters back figured from monitoring of actual excavations and retaining structures; published correlations from other geological environments, such as mass modulus versus RMR; or semi-theoretical approaches such as Hoek’s approach of estimating mass modulus from Hoek- Brown parameters. Unfortunately, when one scratches the surface many of these correlations and guidelines are based on scant data and they must be used with great caution.
This paper summarises the deformation and strength parameters the authors currently use for rock mechanics computations in the Sydney shales and sandstones. It is not intended to provide a detailed lithological or petrographic description of Sydney rocks. The reader is directed elsewhere for that information, for example Packham (1969), Chestnut (1983), Pells (1985), Pells (1993), Pells et al (1998), McNally & McQueen (2000), McNally & Franklin (2000), etc. Rather, the purpose of this paper is to improve the communication between engineering geologists, geotechnical engineers and the construction industry, in particular the tunnelling fraternity, when referring to Sydney rocks.
The paper is divided into four parts.
- The first is a recapitulation of the appropriate process of classification using the Sydney Classification System.
- The second presents typical insitu engineering parameters, which may be appropriate for engineering design once the rock mass has been classified. The tables should not be used to back-figure the rock mass class.
- The third presents typical Q and RMR values for sandstone and shale, as the authors have found that these may help in communicating conditions to practitioners unfamiliar with the Sydney Classification System. However, please note that the authors do not recommend using either the Q or RMR system, or the Sydney Classification System, for the design of tunnel support within these rocks. Several publications highlight the difficulties in using the Q and/or RMR system in Sydney, eg Asche & Cooper (2002), Pells (1997).
- The fourth presents six colour sheets describing the typical engineering geology of Class I/II, Class III and Class IV/V sandstone and then of Class I/II, Class III and Class IV/V shale. Photographs of example rock exposures are included on the sheets to further assist communication. The authors note that there are several locations around Sydney to observe these exposures, including:
- West Pymble Bicentennial Park – Class II to V sandstone;
- M2 tunnel and the Tarpian Cliff at the Opera House – Class I and II sandstone;
- c. Eastwood Brick Pit – Class V to II shale;
- M2 motorway – Class V and IV shale.
The authors hope that practitioners will find this paper useful in their work in Sydney.
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Use of carbon fibre reinforced polymer (CFRP) as an alternative material in permanent ground anchors
Steel tendon ground anchors are an integral construction technique for numerous civil engineering applications ranging from deep excavation support to resistance of structural uplift and overturning of superstructures. Failures of steel strand ground anchor systems are rare but, when they occur, corrosion and human error are the primary reason. Several methods of minimising anchor system corrosion have been adopted over time to minimise ingress of corrosive substances. However, anchors are still failing due to corrosion. Advancement in the development of corrosion resistant materials has been at the forefront of materials research. In this respect, research and development of FRP materials is enabling the progress of providing the industry with a more potentially robust anchor system aimed at eliminating current limitations encountered with steel strand ground anchors.
This paper provides an overview of current best practices for the application of permanent ground anchors and investigates the current developments in FRP materials for ground anchor applications as an alternative to conventional steel tendon ground anchors. The paper also provides insight into known areas where further research is required to assist the introduction of FRP ground anchors into standards.
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Landslide Risk Assessment For Geehi Aqueduct, Snowy Mountains
Geehi River aqueduct diverts waters from left bank tributaries of the Geehi River and conveys these flows into Geehi Reservoir to augment the natural and tunnel inflows.
The aqueduct traverses a section of the steep western flank of the Great Divide with deeply incised valleys and contains numerous inverted syphons.
During the construction of the aqueduct problems were encountered with unstable ground in some areas along the bench. As a result extensive subsoil and surface drainage measures were carried out in the vicinity of the Big Tree Creek siphon, Maria creek siphon and previously burst area.
It was found during the latter stages of construction, that numerous joints between the concrete pipes and fittings had developed excessive gaps due to ground movements. A large proportion of the concrete pipes were found, both before and after laying, to have developed longitudinal internal cracks extending from socket end at the crown. A lap welded stainless steel liner has been installed internally to prevent leaks through the cracks and joints.
The section of the aqueduct passing through the Big tree area was known to be a landslip area. This paper describes the investigation, risk assessment and stabilisation process carried out to mitigate the risks. The construction was completed in March 2001.
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Some geomorphological techniques used in constraining the likelihood of landsliding – Selected Australian examples
Techniques for landslide risk management in Australia have evolved considerably since the publication of the first formal process in 1985. The Australian Geomechanics Society recently published the next generation of updated landslide risk documents in 2007. The estimation of landslide likelihood is fundamental to the outcome of the landslide risk management process. However, experienced practitioners still regard this component as one of the most difficult and challenging aspects of the assessment as it requires information about the age of landslides, an understanding of landscape processes and the rate of slope evolution. Such information is difficult to obtain and is often not a core competency among practitioners undertaking landslide risk assessment. In order to provide insight into the methods of estimating and constraining landslide likelihood, a number of different geomorphological approaches are herewith reviewed through a series of selected Australian cases studies. Whilst the case studies highlight inherent limitations and uncertainties they also demonstrate how geomorphological studies can provide validation and constraints to a quantification of likelihood and ultimately risk.
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Making Earth Materials Talk
How Earth materials are used as evidence in crime investigations
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Large strain coupled analysis of geotechnical problems using high-order elements
In this paper high-order triangular elements are implemented in the framework of the Arbitrary Lagrangian-Eulerian method for the analysis of large strain coupled consolidation problems in geomechanics. The theory of coupled consolidation, as well as details of the high-order elements, including quadratic (6-noded), cubic (10-noded), quartic (15-noded) and quantic (21-noded) elements, are discussed. The accuracy and the efficiency of high-order elements in the analysis of undrained problems are presented by solving two classical geomechanics problems. These include the bearing capacity of soil under a footing and the large deformation analysis of a vertical cut subjected to a surcharge loading. Based on the numerical results, it is shown that high-order elements not only improve the accuracy of the solution, but can also significantly decrease the required computational time.
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Reducing geotechnical uncertainty to help manage risk – how to make CPT and vane shear work (together) for you
This paper has explained that one valid reason for using in situ testing in geo-engineering is to improve site investigation data and in doing so to reduce geotechnical uncertainty and risk. This is real and can certainly be achieved; making everybody happy. The impact on reducing uncertainty can be outstanding.
But the paper has also deliberately set out to demonstrate, using just two common test techniques, CPT and Vane Shear, that maybe “in situ ain’t in situ”. It’s not quite that simple – as in situ test data can be wrong. In fact there is potential for poorly implemented in situ testing to be more misleading and risky than other methods simply because people trust it to be correct and may rely on that trust inappropriately.
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Compaction QA limitations: benefits of alternative testing methods
Density testing has been applied widely in quality assurance (QA), yet because of its widespread usage, this now acts as an impediment to the development of alternative methods of testing. Many incorrect inferences are made from density testing. Limitations and issues associated with traditional density testing inferences are shown with case studies. Modern geotechnical and pavement designs are based on modulus and strength values. It is therefore reasonable to investigate the feasibility to use alternative test methods for QA purposes, which measures these parameters directly. A state-of-the- industry study was completed to identify test methods that have the potential to: (a) reliably provide a direct measure of the strength or in-situ modulus value; and (b) offer significant time savings in turnaround time of QA test results. Comparisons of density with alternative in-situ testing show the latter provide significant benefits to the industry.