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Permeability of bentonite and bentonite-sand mixtures
The permeability of bentonite and bentonite-sand is an essential parameter for designing any type of waste disposal or in geo-environmental engineering applications. To design and construct these facilities accurate values of permeability for these bentonite-sand mixtures must be evaluated. For this purpose, a series of various laboratory tests was performed to investigate the coefficient of permeability using direct and indirect test methods derived from consolidation theory using variable liquid limit (1.10 ~ 2.00) of bentonite. Permeability tests were also carried out for dynamically compacted bentonite and bentonite-sand mixtures. In this paper a discrepancy between permeability determined by direct and indirect test methods was identified. In some cases the coefficient of permeability varied to a maximum of about 10 times between the direct and indirect test methods at the same void ratio and also varied within the same method. The void ratio of the bentonite was a key parameter of permeability for bentonite and bentonite-sand mixtures. The specimen manufacture method had no effect on permeability. This study proposes a formula to predict the coefficient of permeability for bentonite slurry by knowing the degree of saturation for a given void ratio.
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Investigation into the transfer mechanism of loads in grouted bolts
A series of push and pull laboratory based tests were used to investigate how the surface profile of resin grouted bolts influenced the load transfer mechanism. The bolts comprised deformed bar having deformation profiles at different heights and different spacing between deformations. The results indicated that peak loads and displacements were directly related to the height and spacing of the deformations. A series of numerical simulations were carried out to confirm the results obtained in the laboratory.
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Soft Soil Site Characterisation by In Situ Testing
The most commonly used in situ testing tool in site characterisation, the SPT, is more than 100 years old. While it’s still a useful tool for many purposes there have been significant advances in technology over those 100 years, including advances in the tools that can be used for geotechnical site characterisation. Some very useful tools have evolved.
This paper discusses some up-to-date methods of site characterisation, focusing on those up-to-date tools that are now available in Australia and some that will be arriving soon. The paper also provides beginners-level guidance on “where to go” regarding interpretation of data that comes from these tools.
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Simulation of the cone penetration test: discrete and continuum approaches
The paper presents the modelling of the cone penetration test using two procedures: a discrete approach and a continuum approach. The discrete approach is based on the Discrete Element Method where a granular material is represented by an assembly of separate particles. Cone penetration has been simulated for both uncrushable and crushable sands. For the continuum approach, the Particle Finite Element Method has been adapted in order to overcome the difficulties posed by the occurrence of large displacements as well as by the geometrical, material and contact nonlinearities of the problem. Both single phase and two-phase (coupled hydromechanical) formulations have been developed and applied. Although not exempt from problems, both approaches yield realistic results leading to the possibility of a closer examination and an enhanced understanding of the mechanisms underlying cone penetration.
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Performance of Sewer Pipes with Liner during Earthquakes
Recent earthquakes have shown that liquefaction and associated ground deformations are major geotechnical hazards to civil engineering infrastructures, such as pipelines. In particular, sewer pipes have been damaged in many areas in Christchurch as a result of liquefaction-induced lateral spreading near waterways and ground oscillation induced by seismic shaking. In this paper, the addition of a flexible AM liner as a potential countermeasure to increase sewer pipe capacity was investigated. Physical testing through 4-point loading test was undertaken to characterise material properties and the response of both unlined pipe and its lined counterpart. Next, numerical models were created using SAP2000 and ABAQUS to analyse buried pipeline response to transverse permanent ground displacement and to quantify, over a range of pipe segment lengths and soil parameters, the effectiveness of the AM liner in increasing displacement capacity. The numerical results suggest that the addition of the AM liner increases the deformation capacity of the unlined sewer pipe by as much as 50 times. The results confirmed that AM liner is an effective countermeasure for sewer pipes in liquefied ground not only in terms of increased deformation capacity but also the fact that AM-Liner can prevent influx of sand and water through broken pipes, making sewer pipes with liner remaining serviceable even under severe liquefaction condition.
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Developing engineering intuition
The limitations of our knowledge base result in occasions when “engineering judgement” is required. But what is this, and can it be developed? Engineering and geotechnical training focusses on technical and perhaps managerial aspects but pays little attention to the development of engineering instincts.
This paper explores the concept of engineering intuition and suggests directions that may be pursued by (young) engineers to encourage its growth. This is based on reflections of my own experience and is primarily explored and illustrated within a geotechnical context.