Includes bibliographical references (p. 239-255).

Thesis (Ph. D.)--University of Queensland, 2003. / Includes bibliographical references.

In the discipline of geotechnical Engineering the majority of finite element program users is familiar with the hyperbolic soil model. The input parameters are commonly obtained from a series of triaxial tests. For cohesionless soil ls however, today's sampling techniques fail to provide undisturbed soil specimen. Furthermore, routine triaxial tests can not be carried out on soils with grains exceeding 10 - 15 mm in size.

No description available.

No description available.

Granular materials are abundant in the natural and industrial environment. Typical granular materials are collections of inert, passive particles in which the constituent grains of the material are macroscopic; thus they fill space, are athermal, and interact through only local contact forces. This definition can be broadened to include non-inert particles as well-active particles-in which the grains of an active granular material possess an internal energy source which drives motion. Active granular materials are found in many areas of the biological world, from cattle stampedes and pedestrian traffic flow, to the subterranean world of ant colonies and their collective motion within the nest. We study the rheology and dynamics of inert granular material, and an active granular system of collections of fire-ants, which together we call matter with granularity. In both of these systems we observe bifurcations in the force and flow dynamics which results from confinement effects of the effectively rigid granular materials. In inert granular systems, the onset of flow among particles that are closely packed together causes them to dilate as particles must separate away from each other to accommodate flow. Dilation is a property unique to matter with granularity and other complex fluids in which particles interact locally and occupy space. We explore how dilation influences the inert granular system in situations of local and global forcing: drag of an immersed intruder and avalanche flow respectively. We next study collections of fire ants which also interact with each other locally through contact forces and exclude volume. We study the construction of, and locomotion within subterranean tunnels by groups of fire ants. We find that the traffic dynamics of ants within confined tunnels are significantly affected by tunnel diameter. Reducing tunnel diameter increases the formation of traffic jams due to the inability of ants to pass each other easily. However, we show that jamming within tunnels may have beneficial effects on subterranean locomotion. Individual ants jam there bodies against the walls of vertical tunnels to resist falling. From physics studies of fire ant mobility in confined spaces, we show that subterranean tunnel size has a significant effect on the stability and mobility of ants within these environments.

Thss thesis presents the results of an experimental programme on the static mono-tonic response of cohesive-frictional granular materials. The purpose of this experimental programme was to gain insight into the mechanical behaviour of uncemented sands, and sands with small percentages of cementation. With this objective in sight, the research involved understanding and delineating the e ects of four variables: the intermediate principal stress, stress inclination, cohesion (or cementation), and particle morphology. The hollow cylinder torsion (HCT) apparatus, which allows control over both the magnitude and direction of principal stresses, was used in this study to carry out a series of elemental tests on the model materials. The test results were analysed in a plasticity theory based framework of critical state soil mechanics. Drained and undrained HCT tests were conducted on a model angular sand to understand the combined influence of intermediate principal stress ratio (b) and principal stress inclination ( ). Sand specimens were reconstituted to a given density and confining pressure, and were sheared to large strains towards a critical state. The stresses at the critical state with varying `b' were mapped on an octahedral plane to obtain a critical state locus. The shape of this locus closely resembles a curved triangle. Also these specimens showed increased non-coaxiality between the stress and strain increment directions at lower strains. This non-coaxiality decreased significantly, and the response at the critical state was by and large coaxial. The effect of `b' and ` ' on the flow potential, phase transformation, and critical state was also investigated. At phase transformation, ` ' plays a more dominant role in determining the flow potential than `b'. The shape and size of the critical state locus remained the same immaterial of the drainage conditions. Next, small amounts of cohesion (using ordinary Portland cement) was added to this sand ensemble to study the mechanical behaviour of weakly cemented sands. The peak in the stress strain curve was used to signal the breakdown of cohesion further leading to a complete destructuring of the sand at the critical state. The response of the cemented sand changes from brittle to ductile with increase in confining pressure, while reverses with increase in density and `b'. Stress-dilatancy response for the weakly cemented materials shows the non coincidence of peak stress ratio and maximum value of dilation unlike purely frictional materials. This mismatch in peak stress ratio and maximum dilation diminishes with increase in confining pressure. The peak stress (cemented structured sand) locus and the critical state (destructured) locus were constructed on the octahedral plane from these HCT tests. The critical state locus of the cemented sand when it is completely destructured almost coincides with the critical state locus of the clean sand. Using this experimental data set, some important stress-dilatancy relationships (like Zhang and Salgado) and failure criteria (Lade's isotropic single hardening failure criteria and SMP failure criteria) were benchmarked and their prediction capabilities of such models were discussed in detail. The effect of particle morphology was also investigated in this testing programme. Rounded glass ballotini and angular quartzitic sand which occupy two extreme shapes were selected, and a series of HCT tests at different `b' values were con-ducted. A larger sized CS locus was obtained for angular particles and it encompassed the critical state locus of the spherical glass ballotini. Spherical particles exhibit a predominantly dilative behaviour, however present a lower strength at the critical state. The mobilization of strength as a result of rearrangement of angular particles and the consequent interlocking is higher. Even with contractive behaviour which is reflected in the higher values of critical state friction angle and the larger size of the yield locus for sand. Finally, a series of unconfined compression tests were performed to understand if there exists a scale separation in cohesive frictional materials. Specimens were reconstituted to a range of sizes while maintaining a constant aspect ratio and density. As the specimen size increased, the peak strength also increases, counter to an idea of a generalized continuum for all model systems. The observed secondary length scale (in addition to the continuum length scale) is obverse to the one observed in quasi-brittle materials such as concrete, rock. In order to ascertain the reason behind this phenomenon, a series of tomography studies were carried out on these contact-bound ensembles. The presence of cohesion between the grains brings about an \entanglement" between the grains, which contributes to increase in strength, with increase in the size of the sample. This in e ect bringing forth a second length scale that controls the behaviour of these cohesive frictional granular materials. This experimental data set provides quantification of various aspects of the me-chanical response of both cemented and uncemented granular materials under myriad stress conditions. This data set is also extremely useful in developing and bench-marking constitutive models and simulations.

This thesis provides a report on the numerical analysis of stress distributions within granular materials held in silos and hoppers. Stress distributions within granular materials stored in silos and hoppers have been the subject of research for over 100 years, work starting in this field in 1895 (Janssen). Knowledge of stress distributions within the granular materials contained is essential to allow structural design of the silo and hopper shell and attachments, and to allow estimation of likelihood and location of cohesive arch formation. National design codes for silos and hoppers (including BS EN 1993-4-1:2007 Eurocode 3 and DIN 1055-6:2005-03) are based on approximate techniques that assume vertical and horizontal directions of principal stresses, with constant horizontal stress across the silos. According to the knowledge of the author there are no industrial standards that allow calculation of loading on inserts within hoppers. The objective of the research project is to develop algorithms to predict stresses in hoppers and silos using principal stress arc geometry methods, and implementation of these methods in various silo and hopper configurations including those with inserts for the purposes of aiding flow. The research project algorithms are spreadsheet- and QB64 platform-based, and are able to produce stress distributions within silos and hoppers. This is achieved by extension of the principal stress arc method of analysis. The new algorithms allow prediction of common flow problems and provide new information on structural loading of silos and hoppers, including inserts used to promote flow. The research project models allow estimation of azimuthal stresses within three-dimensional case studies.

No description available.

Texture in crystalline materials, i.e. preferred orientation (PO), is of interest in terms of texture-property relationships and also in X-ray diffraction science because PO can cause serious systematic errors in quantitative phase analysis using diffraction data. The single- parameter, pole-density distribution function (PDDF), proposed by March (1932) to represent PO in diffraction analysis, is used widely it Rietveld pattern-fitting following a suggestion by Dollase (1986). While the March model is an excellent descriptor of PO for gibbsite [AI(OH)3] x-ray powder diffraction (XRPD) data (O'Connor, Li and Sitepu, 1991), the model has proved to be deficient for Rietveld modelling with molybdite [Mo03], calcite [CaCO3] and kaolinite [A12O3.2SiO2.2H2O] XRPD data (Sitepu, 1991; O'Connor, Li and Sitepu, 1992; and Sitepu, O'Connor and Li, 1996). Therefore, the March model should not be regarded as a general-purpose PDDF descriptor.This study has examined the validity of the March model using XRPD and neutron powder diffraction (NPD) instruments operated, respectively, by the Curtin Materials Research Group in Perth and by the Australian Nuclear Science and Technology Organisation at the HIFAR reactor facility at Lucas Heights near Sydney. Extensive suites of XRPD and NPD data were measured for uniaxially-pressed powders of molybdite and calcite, for which the compression was systematically varied. It is clear from the various Rietveld refinements that the March model becomes increasingly unsatisfactory as the uniaxial pressure (and, therefore, the level of PO) increases.The March model has been tested with a physical relationship developed by the author which links the March r-parameter to the uniaxial pressure via the powder bulk modulus, B. The agreement between the results obtained from directly measured values of B and from Rietveld analysis with the March model are ++ / promising in terms of deducing the powder bulk modulus from the March r-parameter.An additional test of the March model was made with NPD data for specimens mounted, first, parallel to the instrument rotation axis and, then, normal to the axis. The results have provided some further indication that the March model is deficient for the materials considered in the study.During the course of the study, it was found that there are distinct differences between the direction of the near-surface texture in calcite, as measured by XRPD, and bulk texture characterised by NPD. The NPD-derived textures appear to be correct descriptions for the bulk material in uniaxially-pressed powders, whereas the XRPD textures are heavily influenced by the pressing procedure.An additional outcome of the NPD work has been the discovery, made jointly with Dr Brett Hunter of ANSTO, that the popular LHPM Rietveld code did not allow for inclusion of PO contributions from symmetry-equivalent reflections. Revision of the code by Dr Hunter showed that there is substantial bias in Rietveld-March r-parameters if these reflections are not factored correctly into the calculations.Finally, examination of pole-figure data has underlined the extent to which the March model oversimplifies the true distributions. It is concluded that spherical harmonics modelling should be used rather than the March model as a general PO modelling tool.