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Fifty years of the ISRM and associated progress in rock mechanics
The 12th Congress of the International Society for Rock Mechanics (ISRM) was held in Beijing, China, in October 2011 in the fiftieth year of the life of the Society which was established formally on 24 May 1962 in Salzburg, Austria. This paper which is a slightly revised version of one presented at the Congress (Brown, 2011), discusses the emergence of rock mechanics as a distinctive engineering and scientific discipline, the state and achievements of the discipline at the time the ISRM was founded in 1962, the events leading up to the formation of the Society, the development and achievements of the Society in the 50 years since 1962 and the progress made in the discipline of rock mechanics and rock engineering since that time.
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Estimation of drainability and its effect on the design moisture content of base course material
Climate, groundwater level, permeability and drainage conditions play a key role in the determination of the design moisture content of base course material in pavement design. Most of Western Australia (WA) has an arid or semi-arid climate. Therefore, moisture content close to the Optimum Moisture Content (OMC) is usually used for the Design Moisture Content (DMC) for sealed roads. In fact, moisture content is unlikely to be constant due to water penetration from surface failures or unusual water precipitation. Thus the material should have suitable drainability to be able to dissipate possible excess moisture content. The natural material for base course in WA can have a relatively high percentage of cohesive fines content (fraction smaller than 0.075 mm size) that limits drainability. In order to improve estimations of DMC, this paper presents a review of the drainability potential concept and its empirical estimation method. This is followed by the development of an analytical method of drainability potential estimation. The results of the drainability potential using the two methods, applied to common base course materials, are compared with their corresponding design moisture content, as required by material specifications in WA. This comparison provides information to allow a more accurate determination of DMC for the base course material.
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Classification of sandstones and shales in the Sydney region: A forty year review
The classification system developed in 1978 by a sub-committee of the Australian Geomechnics Society in association with guideline allowable bearing pressures on the Triassic sandstones and shales of the Sydney Basin has proven to be useful as a communication tool on many and varied projects in Sydney and its surrounds. However, the classification system has also been misused.
In this 2nd update of the original paper, the authors:
- indicate uses of the associated classification system, or components thereof, for design of prestressed ground anchors, and for preliminary groundwater analyses,
- show that a modified system is appropriate for linkage to tunnel support design,
- document why the system should not be used in assessments of slope stability, excavatability and rock cutting, and
- expand the guidelines for foundation bearing pressures and socket side shear values based on extensive research testing, and field experience, gained in the 40 years since the original publication.
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2022 AGS Victorian Symposium
Digital Geotechnics
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Layer Identification and Strength Interpretation in Clay from Penetrometer Data
Penetrometer tests are used widely for offshore in situ site investigations and for soil characterisation in laboratory model tests. This paper presents a summary of two PhD dissertations and the work of a Research Fellow on penetrometers in layered clays. The continuous penetration responses of the commonly used cone penetrometer; and two increasingly used full-flow penetrometers (T-bar and ball) have been explored. Single layer, two-layer (soft-stiff and stiff-soft) and three- layer (soft-stiff-soft and stiff-soft-stiff) clay deposits have been considered. The investigations have been carried through large deformation finite element analyses and centrifuge model tests. Interesting and critical soil failure mechanisms are illustrated. Design frameworks are provided for the identification of layer boundaries, and interpretation of undrained shear strength of each identified layer.
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Are the AS2870 standard designs for residential rafts on reactive clay satisfactory?
The standard raft designs set out in AS2870 are adopted for a significant proportion of residential buildings being built around Melbourne (if not in other Australian cities). Of recent years there has been increasing media coverage relating to the poor performance of footings for residential buildings, particularly in areas underlain by Newer Volcanics basaltic clays. There are many aspects which govern the performance of footings founding on or in reactive clays, and questions regarding the appropriateness of the recommendations in AS2870 are being raised. One such question is whether or not the standard raft designs in AS2870 are satisfactory for reactive clay sites. This paper presents the results of three dimensional finite element soil structure interaction analyses of the performance of standard type waffle and stiffened rafts founded on reactive clay. The performance of the rafts analysed is shown to be unsatisfactory with respect to vertical differential movement and structural capacity when subjected to design characteristic surface movements. Whilst significantly more analyses and research is required, the results of these analyses has significant implications for all of the standard footing designs contained in AS2870 for reactive clay sites. This is particularly relevant given the projected levels of population growth in the coming years in the greater Melbourne area which are underlain by highly reactive basaltic clays.
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Practical Considerations For The Application Of A Survival Probability Model For Rockfall
Rockfall fragmentation is a common and very complex phenomenon that is still inadequately understood and rarely modelled. When falling rock blocks break upon impact, their shape and size change and the kinetic energy is distributed amongst fragments. To efficiently design mitigation measures, it is necessary to adequately account for fragmentation when modelling rockfall trajectories. To do so, a better understanding of the fragmentation process, its occurrence and its likely outcomes is needed. The authors have recently proposed a novel model which can predict the survival probability (SP) of brittle spheres upon impact from the statistical distribution of material parameters, obtained by standard quasi- static tests (Brazilian tests and unconfined compression tests). The model predicts two Weibull parameters (shape parameter -m- and scale parameter – critical kinetic energy) that are used to define the SP. The model is based on theoretically-derived (from Hertzian contact theory) conversion factors used to transform the critical work required to fail disc samples in quasi-static indirect tension into the critical kinetic energy to cause failure of spheres at impact in vertical drop tests. The objective of this paper is to provide some practical insights into this model in relation of the analysis of the Brazilian test results and the number of Brazilian tests required to achieve an acceptable prediction. A first analysis highlights the importance of distribution of forces required to break the specimens in Brazilian tests and a common statistical based outlier removal methodology was applied to reduce the experimental error associated with the operator. After eliminating the outlier data, the quality of prediction is improved and, in particular, the influence of the specimen diameter used in Brazilian compressions to derive the model input parameter is significantly reduced. This latter point implies that the size effect is adequately captured. The second analysis reveals the highest variability for batches with low number of tests and a progressive reduction as the number of sampled test increases. Based on these results, it is suggested to use at least 30 Brazilian tests and remove outliers using the simple statistical approach presented in the paper (with of 0.5 or 1.0).
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Collaboration Of Refurbishment Of Tunnel Boring Machines (TBMS) For The KVMRT Putrajaya Line
Riding on experience and lessons learned from the previous SMART tunnel in Kuala Lumpur, Gamuda collaborated with Herrenknecht (equipment manufacturer) and Ruhr University to develop a safe tunnelling method in order to tackle the challenging Karstic Limestone on the Klang Valley Mass Rapid Transit (KVMRT) Kajang Line (Line 1). Hence, the world’s first Variable Density (VD) TBM was developed. VD TBM uses high-density slurry mixes (HDSM) to provide excavation face support preventing sinkhole and blow outs. The innovative breakthrough had successfully reduced occurrence of incidents in Line 1. Overall, six VD and four Earth Pressure Balance (EPB) were used.
For the Putrajaya Line (Line 2), eight TBMs from Kajang Line were refurbished and upgraded with four additional TBMs ordered from Herrenknecht. Gamuda’s collaboration with Herrenknecht expanded vastly with the TBM refurbishment works. The refurbishment was carried out locally with the intention to grow the local industry and bring in global experts to upskill the local workers through knowledge and technology transfer. Gamuda and Herrenknecht explored and worked with local companies such as Waiko Engineering Works to manufacture and source TBM parts locally. The refurbishment works were successful as all TBMs had completed mining through various mixed geologies namely Karstic Limestone, Granite and Kenny Hill formations without major incidents or significant delays.
This paper discusses Gamuda’s collaboration efforts with the project Client, Herrenknecht (equipment manufacturer), Ruhr University (research academics) and Waiko Engineering (local industry) for the refurbishment works and actual findings from Line 2. Recommendations based on the findings were also presented for reference in future works.