AGS NSW Research Award 2017
for Research in Geotechnical Engineering or Engineering Geology Presentations
Adnan Sufian, Chongpu Zhai, Kirti Choudhary and Thanh Trung Nguyen
As part of their ongoing support of academic institutions and students, the Sydney and Newcastle Chapters of the Australian Geomechanics Society are offering the prestigious AGS NSW Research Award for research in Geotechnical Engineering or Engineering Geology.
The award aims to provide a forum for research students from NSW universities to showcase their research to the wider Geotechnical Community. Abstracts for the below presentations can be viewed over page.
This year three (4) research award finalists have been chosen to provide their presentations to the wider geotechnical community and they are:
Thanh Trung Nguyen
Microstructural heterogeneity in granular materials
The heterogeneity associated with the interparticle contact network and the pore space of granular materials is characterised in static and deforming assemblies. The interparticle contact network provides insights into the nature of stress transmission and the microstructural origins of shear strength, while the pore space provides geometric perspectives on fluid flow, water retention and deformation characteristics. Characterising the heterogeneity provides an avenue to develop better predictive models of soil behaviour, which are rooted in the underlying physical interaction of individual soil particles.
Conduction measurement systems for granular materials
In geotechnical engineering, the conduction property of granular materials is of importance in diver applications including geothermal energy , soil probing , sustainable agriculture, slope stability foundations for high-rise buildings etc. Granular materials are commonly used to store, convert, capture, and produce energy under complex conditions. These conditions often involve interactions with retained water, severe heterogeneity, high stresses, great temperature variation, thermal expansion and swelling of materials. Under these conditions, it is fundamentally important to investigate how the geo particles interact with each other thus being able to Control the performance of these granular systems which are encumbered by complex multi-physics interactions of matter and structure across a large range of length scales. For example, the typical shear problem of the Hostun sand analysed at different length scale. The contact behaviour at lower scales dominates the phenomena of the sands at upper scales. Particularly, the microstructures of sand grains, represented by surface roughness bring about strong interconnections of multi-field coupling. The source of these phenomena can be traced back to the micro-scale, which is significantly smaller than the device scale, and even to properties below the nano-scale.
Laboratory evaluation of the smear zone based on measurement of excess pore water pressure dissipation towards a vertical drain
An experimental investigation of the subsoil is of paramount importance before commencing any construction project to assess its bearing capacity. If the shear strength of the soil is found to be unsuitable, ground improvement solutions are to be adopted for improving its engineering characteristics. These ground improvement techniques typically include dynamic grouting, blasting, surface compaction and preloading. A popular and common ground improvement technique is to install an array of prefabricated vertical drains (PVDs) in the soft ground. These drains are usually made of a plastic core with a longitudinal channel which is encapsulated by a sleeve made out of natural or synthetic fabric. Since the horizontal permeability of soil (especially in clays) is higher than their vertical permeability, vertical drains reduce the consolidation time of the soil by providing an alternate radial drainage path thus making the construction schedule much shorter.
The process of installation of PVD’s in the soil consists of inserting the drain inside the soil while it is housed inside a steel mandrel. This process of insertion causes reconstitution of soil around the drain leading to the development of a disturbed zone commonly referred to as the smear zone.
The existence of the smear zone leads to an increase in the time for consolidation due to decreased lateral permeability. The estimation of smear zone radius usually involves measuring the soil permeability or the moisture content (Onoue et al.,1991; Sharma & Xiao, 2000; Sathananthan & Indraratna, 2006). Bergado et. al. (1991) also proposed a back-calculation method by fitting consolidation curves obtained in the laboratory to estimate the smear zone. These techniques usually involve extracting small samples from the soil-drain system at various radii and then testing each of them for permeability or moisture content. At least two specimens are required in such cases.
In this paper, we propose a new method of determination of smear zone based on the gradient of pore water pressure in the radial direction. Using this method, the smear zone radius can be determined in situ in the field provided sufficient piezometers are installed.
Thanh Trung Nguyen
Challenges and solutions toward natural prefabricated vertical drains
In recent years, natural fibres such as jute and coir are emerging as a reasonable alternative to synthetic materials because they do not only have favourable engineering characteristics but also degrade biologically over time. Of promising applications of those environmentally friendly materials, natural prefabricated vertical drains (NPVDs) have received considerable attention. This paper summarises existing issues which are hampering the novel drains from a wider application, followed by studies carried out by the author to overcome those limitations. Particularly this includes: (1) hydraulic properties of NPVDs considering macro and micro features; (2) a novel numerical approach to capture micro-hydraulic behaviour of fibre drains considering fluid-fibre interaction; (3) biodegradable characteristics of NPVDs exposed to saturated soft clay; (4) analytical and numerical solutions to incorporate biodegradation of NPVDs into consolidation of soil.
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