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During soft ground tunnel construction, if the face pressure of a tunnel boring machine is not strictly controlled, excessive ground movements will propagate vertically upwards causing significant damage to adjacent buried infrastructure and surface structures. In order to investigate the face pressure - ground deformation relationship for tunnels in sands, the construction process was modelled using the technique of geotechnical centrifuge modelling and the resulting ground deformations were recorded using digital image correlation. In these tests a unique tunnel face boundary condition was developed which allowed the boundary condition to be initially set as a zero strain condition before it was transformed into a load-controlled boundary to investigate the instability of the face. Tests were preformed at four different burial depths in dry sand, corresponding to cover depths of 0.5, 1, 1.5, and 2 times the tunnel diameter. These results indicate that the face pressure at failure is largely independent of burial depth over the values tested. The ground deformation at the onset of tunnel face instability was found to be very small, and once initiated, the zone of ground deformations was observed to propagate upwards in a narrow chimney in front of the tunnel until it reached the ground surface causing subsidence. Further tests investigated the variation in ground deformations to be expected if a tunnel were to be passing through more complex ground conditions, including unsaturated sand, saturated sand, and the unique case of sand / clay mixed ground conditions. Ground deformations at tunnel face instability were much lower for the case of unsaturated sand, than for either the saturated or dry cases which showed broadly similar responses. In the mixed ground condition of a clay layer over topping a sand layer, the clay layer was found to only influence the tunnel face pressure – deformation response if the bottom of the clay layer was closer than 0.5 diameters above the tunnel crown. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-12-20 15:09:06.156

Understanding the deformation mechanisms of soils and geosynthetics in response to the formation of a void below a geosynthetic-reinforced soil is crucial to provide efficient designs of geosynthetic-reinforced soil systems such as embankments and landfill liners. Centrifuge modelling of the soil and geosynthetic behaviour was conducted using a trapdoor to simulate the formation of a void in a controlled environment at realistic stress levels. A plane-strain model allowed visual observations of the deformation mechanisms using Particle Image Velocimetry. Granular soils and model clay liners were tested, as would be relevant to embankments and landfills respectively. These soils were tested with and without the reinforcement to evaluate the benefit provided by the geosynthetic. Detailed analysis of the centrifuge test results showed that arching significantly reduces the stress at the base of the soil when a void forms; this mechanism is due to stress redistributions and not the formation of a physical arch. A new method to reliably predict this reduction was provided by calculating the coefficient of lateral stress on the failure plane based on the observations of a continuous convex arc of major principal strains above the void, and the assumption that this is indicative of the stress behaviour. The observed results were also used to address the limitations in the current design methods related to the fill behaviour. Expansion in the soil was confined to a parabolic zone above the void estimated from the soil dilatancy, rather than a single, unique coefficient of expansion in the deforming soil. The zone of subsidence was characterised by the combination of a vertical prism and funnel to the surface, with the surface settlement profile better described by a Gaussian distribution rather than the parabolic profile used previously. An adaptation to the design methods for use with compacted clay liners was proposed by considering the clay as a beam with the maximum strain related to curvature and not elongation, and calculating the applied stress on the geosynthetic ignoring the clay arching. Analysis and interpretation of the centrifuge tests has thus given new insight into the soil and geosynthetic behaviour based on visual observations relevant to how these systems deform in practice. This has allowed the recommendation of more efficient design procedures and consequently will facilitate better predictions of geosynthetic-reinforced soil behaviour above voids.

The purpose of this study was to evaluate the suitability of using an existing 25-ft radius centrifuge as a dynamic flight simulator for “full mission” F/A-18 strike fighter mission training with respect to the representativeness of pilot-perceived motion and acceleration cues. The methodology employed in this study consisted of analyzing F/A-18 mission tasks, collecting pilot opinion surveys of important sensory cues needed in simulator training, and conducting an analysis of human pilot perceptual problems caused by centrifuge motion constraints. This study identified a number of issues indicating that a centrifuge-based flight simulator shows limited potential for use in “full mission” F/A-18 training scenarios. Specifically, there is a fundamental mismatch between the 6 degree-of-freedom mission-representative acceleration environment experienced in the aircraft and the 3 degree-of-freedom acceleration environment the centrifuge is able to provide. The centrifuge is not optimized for the typical acceleration environment experienced during F/A-18 missions and has significant limitations in “near one g” and “near zero g” flight conditions. Additionally, the centrifuge causes a variety of undesired, unrealistic, and debilitating vestibular artifacts that are not consistent with what a pilot experiences in the aircraft when performing the same mission task, degrading the effectiveness of training. Despite its limited suitability as a “full mission” F/A-18 simulator, the centrifuge is an essential physiological training device, shows good potential as a part-task trainer for departure/spin training, and should continue to play a role in the F/A-18 training continuum.

The purpose of this study was to evaluate the suitability of using an existing 25-ft radius centrifuge as a dynamic flight simulator for “full mission” F/A-18 strike fighter mission training with respect to the representativeness of pilot-perceived motion and acceleration cues.The methodology employed in this study consisted of analyzing F/A-18 mission tasks, collecting pilot opinion surveys of important sensory cues needed in simulator training, and conducting an analysis of human pilot perceptual problems caused by centrifuge motion constraints.This study identified a number of issues indicating that a centrifuge-based flight simulator shows limited potential for use in “full mission” F/A-18 training scenarios. Specifically, there is a fundamental mismatch between the 6 degree-of-freedom mission-representative acceleration environment experienced in the aircraft and the 3 degree-of-freedom acceleration environment the centrifuge is able to provide. The centrifuge is not optimized for the typical acceleration environment experienced during F/A-18 missions and has significant limitations in “near one g” and “near zero g” flight conditions. Additionally, the centrifuge causes a variety of undesired, unrealistic, and debilitating vestibular artifacts that are not consistent with what a pilot experiences in the aircraft when performing the same mission task, degrading the effectiveness of training.Despite its limited suitability as a “full mission” F/A-18 simulator, the centrifuge is an essential physiological training device, shows good potential as a part-task trainer for departure/spin training, and should continue to play a role in the F/A-18 training continuum.

Austin, Texas consists of highly expansive soils that have caused failures in many structures. Minimizing the detrimental effects of expansive soils on structures requires that the swelling of these soil(s) is quantified accurately, efficiently, and timely. A testing procedure was developed to directly measure soil swelling using centrifuge technology by Plaisted, 2009. This testing procedure was developed in order to reduce the test duration while generating more swelling data relative to conventional tests that directly measure swell. However, the new procedure was incapable of obtaining in-flight swell data, resulting in the need to develop a procedure to directly measure swell during centrifugation. The objectives of this study were to update the testing procedure developed by Plaisted, 2009 by incorporating the use of an in-flight Data Acquisition System (DAS) that would produce accurate and repeatable results; and use the updated testing procedure to quantify the effects of compaction conditions on swelling for three expansive soils in the Austin area (Eagle Ford Shale, Houston Black Clay, and Taylor Clay). A DAS consisting of linear position sensors, analog to digital converters, JeeNode Arduinos, and an accelerometer was developed and installed within the centrifuge. Specimens were compacted at various water contents, and densities, and subjected to different g-levels. The effects of g-level, compaction water content, compaction dry unit weight, and soil type were determined by comparing the 34 hour swell percentages for the compacted specimens. The results of this study showed that in-flight monitoring of clay swelling could be successfully implemented in a comparatively small centrifuge, and that the data collected from the DAS was accurate and repeatable. Swelling of tested soils was found to be sensitive to changes in water content around optimum, with specimens compacted wet of optimum swelling less than specimens compacted dry of optimum. A 6% increase in relative compaction was found to negligibly affect the swelling. Finally, variations in confinement and compaction conditions were found to have a greater effect on swelling for soils that are more expansive in nature compared to soils less expansive in nature. / text

Three testing procedures were developed in this research to allow expeditious characterization of soil unsaturated flow properties using steady state centrifuge methods. The first testing procedure, referred to as the “instrumented” procedure, focuses on using in-flight measurement of the suction and volumetric water content of soil samples under centrifugation. The measurements are used to calculate the soil water retention curve and hydraulic conductivity function (K-function) of soil samples. A good agreement was found between results determined using the “instrumented” procedure and standard testing methods. Several possible sources of inaccuracy were determined with the “instrumented” procedure. The void ratio, the changes of which were not measured, was found to decrease during centrifugation and the lower boundary condition, which was not accounted for in the evaluation, was found to affect a large portion of the sample. In order to improve the accuracy of results, two additional testing procedures were developed that accounted for these issues and incorporated the void ratio of the soil as an additional variable. The first additional procedure was used to measure the soil water retention surface (SWRS) of soil samples while the second was used to measure the unsaturated hydraulic conductivity surface (K-surface) of soil samples. Both new procedures, referred to as the “hydrostatic” and “imposed flow” procedures, were used to characterize the unsaturated flow properties of a low plasticity clay (“RMA” soil). The unsaturated flow characteristics of the RMA soil were evaluated for a wide range of void ratio and three compaction moisture conditions. As a result, the effects of void ratio and compaction moisture content on the unsaturated flow characteristics could be determined for the RMA soil. The compaction water content was shown to have significant effects on both the retention behavior and the unsaturated hydraulic conductivity of the RMA soil. In general, increases in compaction water content resulted in a decrease of large pore sizes in the soil, resulting in higher water retention and lower unsaturated hydraulic conductivity. The void ratio was found to have comparatively lesser, but still significant, effects on both retention and conductivity characteristics. Specifically, decreases in void ratio were shown to reduce the unsaturated hydraulic conductivity. In addition, decreases in void ratio were shown to result in either increases or decreases on the soil water retention, depending on the level of suction in the soil. A good agreement was found between results obtained using standard methods and those from the hydrostatic and imposed flow procedures. Accordingly, steady state centrifuge methods were ultimately found to provide a both expeditious and accurate method for characterizing the unsaturated flow properties of soil. / text

Landslides occur both onshore and offshore. However, little attention has been given to offshore landslides (submarine landslides). Submarine landslides have significant impacts and consequences on offshore and coastal facilities. The unique characteristics of submarine landslides include large mass movements and long travel distances at very gentle slopes. This thesis is concerned with developing centrifuge scaling laws for submarine landslide flows through the study of modelling submarine landslide flows in a mini-drum centrifuge. A series of tests are conducted at different gravity fields in order to understand the scaling laws involved in the simulation of submarine landslide flows. The model slope is instrumented with miniature sensors for measurements of pore pressures at different locations beneath the landslide flow. A series of digital cameras are used to capture the landslide flow in flight. Numerical studies are also carried out in order to compare the results obtained with the data from the centrifuge tests. The Depth Averaged Material Point Method (DAMPM) is used in the numerical simulations to deal with large deformation (such as the long runout of submarine landslide flows). Parametric studies are performed to investigate the validity of the developed centrifuge scaling laws under the initial and boundary conditions given in the centrifuge tests. Both the results from the centrifuge tests and numerical simulations appear to follow the proposed centrifuge scaling laws, which differ from the conventional centrifuge scaling laws. The results provide a better understanding of the centrifuge scaling laws that need to be adopted for centrifuge experiments involving submarine landslide flows, as well as giving an insight into the flow mechanism involved in submarine landslide flows.

This project was concerned with the analysis and development of a decanter centrifuge. The aim of the project was to increase the understanding of the operation of the machine, and identify and implement methods of improving the performance. A comprehensive breakdown of the power consumption of a GTech-Bellmor 1456 Centrifuge Decanter was completed. There are four components of the power consumption in a decanter centrifuge: friction during product transport, viscous and kinetic losses during feed acceleration, inefficiencies in power transmission components, and aerodynamic losses, known as windage. A mathematical model was developed to predict the power, torque, and axial force required by product transport. A relationship for the power consumed during feed acceleration was derived from first principles. The power transmission losses are comprised of inefficiencies in the motors, belt drives, gearbox, bearings, and seals; each of these was quantified. The windage has two components: the surface drag on the bowl as it rotates in an annular space and the pressure drag on external protrusions. The windage was predicted empirically and computationally. Methods that were identified for improving the decanter centrifuge were: reduce the mass of bowl and scroll, improve wear resistance, reduce the coefficient of friction of the bowl wall and scroll faces, optimise scroll geometry, redesign the feed accelerator to increase acceleration efficiency, implement control of the bowl speed, differential speed, and pool depth, and recess the bolt heads on the bowl and cover the third phase ports. An analysis of several worn centrifuges revealed that the majority of the wear occurs on the scroll, bowl wall, accelerator, and solids discharge ports. An experiment was developed to recreate the wear conditions inside a centrifuge. A high pressure abrasive film was forced between materials moving relative to each other. Similar results were observed for acetel, UHMWPE, and 316 stainless steel when using a pin-on-disk wear test rig. A new composite bowl was developed for two main reasons, weight reduction, and improved wear and friction characteristics. The full design process was applied to the bowl and several concepts were generated for a new scroll. The design of the bowl included conceptual design, material selection, material testing, constructing scale models, and the manufacture of a full-size bowl for a GTech-Bellmor 1456 Centrifuge Decanter. The potential for using composite materials in decanter centrifuges was demonstrated. The manufacturing method developed during this project was novel and produced parts suitable for use in high-speed rotating machinery. The feed accelerator analysis consisted of three components: theoretical, experimental, and computational analysis. Three feed acceleration mechanisms were identified: viscous dissipation, impulse force, and mass flow induced velocity. An experimental method was developed to examine decanter centrifuge feed accelerator designs. The method allowed for the measurement of efficiency and high-speed photography of the flow between the accelerator and the rotating pool. The order of best to worst performing of the six tested designs was Modified Disk, Disk, Plate, Conical, Drum, and Esbjerg. The feed accelerator was modelled using ANSYS-CFX 14.5 and compared to the experimental results. There was excellent agreement between the flow in the annular space observed using high-speed photography and the paths predicted using the computational model. A parametric study of the Drum and Disk feed accelerator designs was undertaken using the computational model. It was found that increasing the surface area of the port faces of the Drum accelerator and increasing the discharge angle and discharge radius for the Disk accelerator improved the performance.

Rainfall induced granular flow slides pose a significant risk in many areas of the world. These failures, characterized by the sudden release of material in a fluid-like manner, are the result of static liquefaction occurring in these slopes. The static liquefaction phenomenon has been linked to instability. Instability behaviour is primarily studied under undrained triaxial conditions, and although many instability theories have therefore been defined in this stress space, these have been shown to also extend into plane strain conditions. In order to further investigate this behaviour under these stress conditions, Wolinsky et al. (2013) developed a tilt-table soil box for use in a geotechnical centrifuge to analyze instability in infinite slope soil models. This testing apparatus has been used to simulate instability in plane strain under both dry and saturated soil conditions. Stress-controlled experiments were performed on dry infinite slope soil models to investigate the effects of both void ratio and effective stress on instability behaviour. By performing these tests dry, this test apparatus provides the ability to decouple the triggers of instability from the corresponding response in pore pressure and the consequences. The results of this testing confirmed that the instability line angle is a function of both void ratio and effective stress. As the void ratio decreases and effective stress in the soil model increases, the resulting instability line angle will increase. This testing also demonstrated typical stress-dilatancy behaviour in these infinite slope models, characterized by contractive response in loose soils and dilative response in dense soil subject to increasing shear stress. Secondly, this testing apparatus was used to investigate the effects of seepage force on instability behaviour in granular slopes through the introduction of groundwater seepage in the form of a rising groundwater level. Although the results illustrated shear and volumetric response to these increased pore water pressures, these were not significant enough to initiate instability and the resulting pore water response leading to failure. It has been determined that this apparatus must be further adapted to dissipate the matric suctions developed above the water table during groundwater rise. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-12-03 21:06:56.806