The behaviour of cohesionless soils is known to be influenced by the method of reconstitution. It is generally accepted in the literature that different reconstitution methods produce samples of varying fabric and thus samples of varying behaviour. Very little evidence has been presented to validate this statement. The main aim of this is thesis is firstly to observe the fabric of in situ and reconstituted gold tailings samples and secondly to investigate the difference in behaviour between these samples at the same state. The investigation focused on testing in situ and reconstituted gold tailings samples obtained from 3 positions on a tailings dam; pond, middle beach and upper beach. Laboratory reconstitution methods included moist tamping and slurry deposition. Fabric analysis involved the use of SEM images to classify the observed differences in the fabric of the undisturbed and reconstituted gold tailings samples. A particle interaction model based on the observed fabric was postulated to explain the differences or similarities in behaviour. The scope of behaviour investigated included sedimentation, collapse and swell, consolidation and compressibility, creep, stiffness and shear behaviour. The fabric analysis indicates that differences in the fabric of undisturbed and reconstituted gold tailings samples are visible. Moist tamping produces an aggregated fabric while slurry deposition yields a homogeneous fabric similar to that of the undisturbed samples. Comparison of behaviour indicates that neither moist tamping nor slurry deposition can replicate the behaviour of the undisturbed sample fully. Consolidation and compression is a function of the fabric while friction angle is independent of the fabric. Available shear strength and liquifaction potential is also affected by the preparation method and the resulting fabric. / Thesis (PhD)--University of Pretoria, 2009. / Civil Engineering / PhD / Unrestricted

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<p>This thesis investigates the effects of sample preparation methods, which has substantial influence on the internal structure or fabric of the sample, and interparticle locking on the behaviour of sand through experimental study. Extensive laboratory tests were conducted on two sands (namely, Ottawa sand and crushed limestone) with distinct particle shape and surface texture, using a Bishop-type triaxial testing system.</p><p>A total of eight sample preparation methods were used to fabricate specimens with different initial fabric, with specimens being fabricated using water pluviation, moist tamping, and moist rodding. The experimental data reveal that sample preparation methods have significant effect on both deformation characteristics and shear strength of sand, in addition to the density and the effective confining pressure applied to the specimens. More specifically, water pluviation and moist tamping tend to yield specimens of high anisotropy and large dilation, which in turn results in higher friction angle in conventional triaxial compression. The effect of sample preparation methods was also observed from undrained tests on saturated sand.</p><p>Laboratory tests on crushed limestone consisting of angular particles demonstrate that strong interparticle locking may develop owing to particle angularity. The shear resistance of sand with angular particles has contributions from interparticle friction, dilatation and interparticle locking. Moreover, interparticle locking, which largely exists at the peak shear resistance of sand but vanishes with dilation at large deformation, exists under both low and high stress levels investigated in this study. A conceptual model was proposed to take into account the energy consumption associated with breaking interparticle locking during deformation when estimating the dilatancy and strength of granular soils.</P><P>The behaviour of sand along proportional strain paths was also investigated, with the focus being placed on strain softening and material instability in the context of Hill's second order work. Depending on the strain path or the deformation history, a dilatant sand displaying hardening and stable behaviour under isochronic (undrained) conditions, which is often used as a reference in soil mechanics, may succumb to unstable flow type behaviour along dilative strain paths. More specifically, when the imposed rate of dilation exceeds the inherent rate of dilation of the material, a dense sand specimen will have flow failure similar to that of a saturated loose specimen subjected to undrained compression. On the other hand, a loose sand may not have a flow failure when it is forced to have contractive volume change along imposed strain paths.</P> / Thesis / Master of Science (MSc)

The behavior of the ballast particles during their interaction with tamping tines in tamping operation is studied by developing a simulation model using the Discrete Element Model (DEM), with the aim of optimizing the railroad tamping operation. A comprehensive literature review is presented showcasing the applicability of DEM techniques in modeling ballast behavior and its feasibility in studying the fundamental mechanisms that influence the outcome of railroad tamping process is analyzed. The analysis shows that DEM is an excellent tool to study tamping operation as its important and unprecedented insights into the process, help not only to optimize the current tamping practices but also in the development of novel methods for achieving sustainable improvements in the track stability after tamping. The simulation model is developed using a commercially available DEM software called PFC3D (Particle Flow Code 3D). A detailed explanation is provided about how to set up the DEM model of railway ballast considering important parameters like selection and calibration of particle shapes, ballast mechanical properties, contact model, and parameters governing the contact force models. Tamping operation is incorporated into the simulation model using a half-track layout with a highly modular code that enables a high degree of adjustability to allow control of all process parameters for achieving optimized output. A parametric study is performed to find the best values of tine motion parameters to optimize the linear tamping efficiency and a performance comparison has been made between linear and elliptical tamping. It is found that squeeze and release velocity of the tines should be lesser for better compaction of the particles and linear tamping is better compared to elliptical tamping. / Master of Science / Railway track stability is the resistance of the tracks to deformation and is affected by the rail traffic, ballast fouling (contamination of ballast) and the changing environmental conditions. The track stability depends on the normal and frictional support provided by the ballast to the sleepers. Non-uniform ballast consolidation below the railway sleeper results in erratic wheel-rail contact forces, low traffic speeds, poor ride quality, and derailments. Thus, tamping is a railway track maintenance method done periodically on the railway tracks to ensure track stability. Tamping process involves compacting the railroad ballast underneath the sleeper. The sleeper is lifted by a desired height and then vibrating tamping tools called tines are inserted into the ballast below the sleeper to fill the void created by lifting of the sleeper and the sleeper is dropped back on to the ballast. So, it is important to understand the ballast mechanics, dynamics and ballast’s behavioral response to the tamping operation. Since, large scale experiments such as this are difficult, this operation has been simulated in a commercially available software called PFC3D using a Discrete Element Model (DEM) to represent the railway ballast. It is shown through a simulation that though spherical particles provide better computational efficiency, they cannot capture the exact ballast behavior like clumps (a collection of spherical pebbles). So using clumps to represent ballast, efforts are made to optimize the linear tamping efficiency. This is done by changing the values of parameters like tine amplitude, tine frequency, insertion velocity and squeeze velocity and finding their optimum values. Linear tamping results are compared with elliptical tamping. Thus, an optimum tamping cycle would help save money spent on the track maintenance activities.

The development of Discrete Element Model (DEM) of railway ballast for the purpose of studying the behavior of ballast particles during tamping is addressed in a simulation study, with the goal of optimizing the railroad tamping operation. A comprehensive literature review of applicability of DEM techniques in modeling the behavior of railway ballast is presented and its feasibility in studying the fundamental mechanisms that influence the outcome of railroad tamping process is analyzed. A Discrete Element Model of railway ballast is also developed and implemented using a commercially available DEM package: PFC3D. Selection and calibration of ballast parameters, such as inter-particle contact force laws, ballast material properties, and selection of particle shape are represented in detail in the model. Finally, a complete tamping simulation model is constructed with high degree of adjustability to allow control of all process parameters for achieving realistic output. The analysis shows that DEM is a highly valuable tool for studying railroad tamping operation. It has the capability to provide crucial and unprecedented insights into the process, facilitating not only the optimization of current tamping practices, but also the development of novel methods for achieving sustainable improvements in track stability after tamping in the future. Different ways of modeling particle shapes have been evaluated and it has been shown that while using spheres to represent irregular ballast particles in DEM provides immense gains in computational efficiency, spheres cannot intently capture all properties of irregularly shaped particles, and therefore should not be used to model railway ballast particles. Inter-particle and wall-particle contact forces are calculated using Hertzian contact mechanics for determining ballast dynamics during tamping. The results indicate that the model is able to accurately predict properties of granular assemblies of the railway ballast in different test cases. The developed model for simulating tamping operation on a half-track layout is expected to be extended in future studies for evaluating rail track settlement and stability, optimization of tamping process, and performance of different ballast gradations. / MS

The diploma´s thesis deals with evaluation of adjusted track tamping technology and its comparison with currently used technology. This is based on track geometry parameters measuring and its vertical movement on the test section, which was created on double track Břeclav – Přerov near Rohatec station. On this test section one line was tamped with the currently used method within regular maintenance work and the second line was tamped with the adjusted technology. The technology modification is based on application of increased number of tamping tines squeezing strokes, which results in a creation of bigger and more compacted sleeper bed. The point of this thesis is to verify, that the speed of the track geometry parameters degradation is smaller in case of adjusted technology use. Thanks to that it would be possible to extend the maintenance cycles in case of compliance with track parameters maintenance limits and traffic safety.

The work presents a proposal for the technology of production of a pin of gear assambly.The pin is used to position the wheel in a tapered roller bearing. Pin is made of 11 320.3 steel (11 320 5R), which is suitable for cold forming. Based on the study of cold forming and calculations, the methods of upsetting and extrusion were chosen. Most often, several methods are used for fabrication, which are mediated by a combined tool. It can also be made by any of the machining methods.

Rail is a very expensive component of the railway track. Therefore, research methods extending rail life have great economic importance. During the past thirty years and, particularly during the past ten years there has been an increasing awareness throughout most rail networks in the world of the need to introduce improved design criteria, better construction techniques and higher standard track generally. This implies that quality control at all levels is mandatory if these objectives are to be achieved. With the improved understanding of degradation of track, a more complete comprehension of the costs associated with different operating and infrastructure conditions should also be developed, aiding in the determination of efficient maintenance costs and their contribution to access charges. Track and structures together account for 60% of maintenance costs, with 50% of the total being track. The UIC has done a lot of work on comparative performance indicators, and these show what potential savings much be out there for the taking, just by adopting current best practice. The old wisdom is that it's not enough o do things rights; we have to make sure that we do the right things. These developments have largely resulted from the demand for higher speeds particularly in passenger services and the demand to accept heavier axle loads of freight traffic. Whilst the conventional railway track structure is not likely to change significantly over the next ten years there will be a requirement over that period for better quality track infrastructure. This means less rail surface defects, less internal defects and less wheels irregularities. The presence of rail surface defects generally increases the roughness of the track leading to a poor passenger ride and increased safety risk with freight traffic. In addition, rail surface defects will generally increase the degradation rate of other track components; however, not all defects will produce visible track deterioration. Dynamic impacts produced by the rollingstock running over rail surface defects, such as poor welds, will, over time, create continuous rail defects, loosening of fastenings, abrasion and skewing of sleepers, crushing of ballast and loss of formation geometry. It is only in the recent years that the importance of poor welds in track has been identified. Dips and peaks must be recognised as a severe track irregularity that needs to be addressed and removed. Current maintenance activities have little effect on removing misaligned welds in track and the improvement obtained after the maintenance works is generally short lived. On the other hand, straightening operations have proven to solve the problem and maintain the results following 7 months of traffic. As part of this project, a six kilometre test section was selected on the Mt Isa Line and all welds located in this region were monitored for over 9 months to increase the understanding of the effect of individual maintenance activities on the track roughness. Three 2km Divisions were established; each Division had different maintenance activities and levels of intervention completed over the duration of the project. Over 15,000 readings were recorded and analysed. The following conclusions were drawn. The effect of cycle tamping was clearly identified when comparing the means of weld located in Division 1, 2 to the mean of welds in Division 3. Cycle tamping showed to have a significant positive effect on the dipped welds geometry and an increase in severity of peaked welds prior to their correction. Straightening operations completed in Division 1 and 2 reduced the overall mean of weld misalignments. These Divisions were subjected to different levels of straightening intervention however they produced similar results. Division 1 all dips were straightened and Division 2 only dips &gt0.3mm were straightened. This means that no additional benefit, in terms of overall misalignment of welds, can be gained when straightening operations target dips with a misalignment smaller than 0.3mm. Cycle grinding proved to have little effect on the removal of both dips and peaks. In fact, due to the configuration of the grinding machine, grinding operation produced a slight worsening of the dips misalignments and only a minor improvement of peaks. Although long term monitoring of the site may show minor variations in weld geometry performance, after approximately 3.9 Mgt of traffic the mean of dipped welds in Division 1 and 2 appeared to remain unaltered, as Division 3 showed a minor worsening. Furthermore, the mean of peaked welds in Division 1 and 2 appeared to remain unaltered, as Division 3 showed a minor worsening.