Vibration compaction is the most effective way of compacting coarse-grained materials. The effects of vibration frequency and amplitude on the compaction density of different backfill materials (No. 4 natural sand, No. 24 stone sand and No. 5, No. 8, No. 43 aggregates), were studied in this research. The test materials were characterized based on the particle sizes and morphology parameters using digital image analysis technique. Small-scale laboratory compaction tests were carried out with variable frequency and amplitude of vibrations using vibratory hammer and vibratory table. The results show an increase in density with the increase in amplitude and frequency of vibration. However, the increase in density with the increase in amplitude of vibration is more pronounced for the coarse aggregates than for the sands. A comparison of the maximum dry densities of different test materials shows that the dry densities obtained after compaction using the vibratory hammer are greater than those obtained after compaction using the vibratory table at the highest amplitude and frequency of vibration available in both equipment. Large-scale vibratory roller compaction tests were performed in the field for No. 30 backfill soil to observe the effect of vibration frequency and number of passes on the compaction density. Accelerometer sensors were attached to the roller drum (Caterpillar, model CS56B) to measure the frequency of vibration for the two different vibration settings available to the roller. For this roller and soil tested, the results show that the higher vibration setting is more effective. Direct shear tests and direct interface shear tests were performed to study the impact of particle characteristics of the coarse-grained backfill materials on interface shear resistance. A unique relationship was found between the normalized surface roughness and the ratio of critical-state interface friction angle between sand-gravel mixture with steel to the internal critical-state friction angle of the sand-gravel mixture.

L’objectif de cette thèse est de caractériser les mécanismes de déstructuration en surface des sols compactés, soumis à des sollicitations cycliques de roulement. Ces chargements cycliques, générés par le trafic, sont principalement responsables de l’envol de particules fines et poussières sur les chantiers de terrassement. La présente étude est réalisée en collaboration avec la Fédération Nationale des Travaux Publics et le Syndicat Professionnel des Terrassiers de France, dans le cadre de leur engagement volontaire, qui vise à mieux contrôler les consommations en eau sur les chantiers de terrassement, utilisée pour réduire les particules fines en vol. La première partie du rapport consiste à aborder l’évolution des propriétés des sols compactés au moyen de différentes méthodes de compactage, au laboratoire comme in-situ. La méthode de compactage par roulement a été adoptée, à l’échelle du laboratoire, afin de reproduire une rotation des tenseurs de contraintes similaire à celle appliquée in-situ. L’étude a confirmé que la méthode de compactage par roulement proposée permet, à la fois de reproduire une rotation continue du tenseur de contraintes, et de conserver un état de densité moyen proche de celui de la référence de compactage du laboratoire. L’étude microstructurale a souligné que la taille des pores inter-agrégats est gouvernée par le compactage, tandis que la taille des pores intra-agrégats est influencée par l’humidification du sol. L’étude des mécanismes de déstructuration de surface de sol sous sollicitations de roulement, responsables de l’envol, a été effectuée dans la seconde partie de l’étude. Cette partie met en évidence l’influence des cycles de roulement sur l’état de surface du sol compacté et son évolution. Les premiers cycles de roulement génèrent un détachement d’agrégats de grande taille, puis, sous l’effet des passages répétitifs, ces agrégats se décomposent en plus petits agrégats, voire en particules fines sujettes à l’envol. La déstructuration de surface est liée aux conditions de mise en œuvre, à l’état de compacité, au processus du séchage, ainsi qu’au type de sol. La troisième partie de la thèse porte sur l’étude du potentiel d’adsorption et d’infiltration de l’eau dans les sols non consolidés lors de leur arrosage par brumisation. Des corrélations entre la surface spécifique et le potentiel d’adsorption avec la conductivité hydraulique du sol ont été établies. L’analyse de la structure de la surface via le traitement d’images a démontré le phénomène d’agrégation sous humidification, qui est fonction de la composition granulométrique et minéralogique du sol. Sur la base de l'étude d'adsorption et d'infiltration, un paramètre d’arrosage est proposé pour lier les propriétés hydrauliques du sol avec le matériel d’arrosage in-situ / The aim of this thesis is to characterize the soil surface degradation mechanisms of compacted soils subjected to cyclic rolling solicitations. These cyclic loadings generated by traffic are the main responsible of dust emission during earthworks. The present study was carried out in collaboration with “Fédération Nationale des Travaux Publics” and “Syndicat Professionnel des Terrassiers de France“, as part of their voluntary commitment to better control the water consumption during earthworks implementation, and particularly for dust abatement. The first part of the report deals with the evolution of soil compaction properties obtained by using different compaction methods, at laboratory and in-situ scales. The rolling compaction method has been considered, at laboratory scale in order to reproduce a stress tensor rotation similar to that applied in-situ. The study confirmed that the proposed rolling compaction method allows both to reproduce a continuous rotation of the stress tensor, and to maintain an average density state close to that of the laboratory compaction reference. The microstructural study highlighted that inter-aggregate pore size is governed by compaction, while intra-aggregate pore size is influenced by soil humidification. The study of mechanisms of soil surface degradation under rolling loads, responsible for the dust emission, was carried out in the second part of the study. This part demonstrates the influence of rolling cycles on the soil surface state of compacted soil and its evolution. The first rolling cycles generates a pullout aggregates, and then, under the effect of repetitive passages, these aggregates break down into smaller aggregates, or even fine particles with high dust emission potential. Soil surface degradation occurs to be linked to the implementation conditions, the compaction degree, the drying process as well as the type of soil. The third part of the study deals with the water adsorption and infiltration potential of unconsolidated soils during spraying phase by water mist. Correlations between soil specific surface area and adsorption potential with the hydraulic conductivity of the soil have been established. The analysis of the surface structure via image processing demonstrated the aggregation phenomenon under humidification, which is a function of the granulometric and mineralogical composition of the soil. Based on the adsorption and infiltration study, a spraying parameter is proposed to link the hydraulic properties of soil with the spraying system used in-situ

A pavement construction designed to cope with the different type of traffic loads; it is exposed to and at the same time it can resist the effect of the climate. A road structure consists of sub- and superstructure which is divided by a boundary known as terrace. During the construction of unbound layers (base course and sub-base course) in the superstructure, it is always ensured that the material meet the requirements for bearing capacity and the degree of compaction. These parameters are controlled by various laboratory tests and control methods. To obtain increased knowledge of the material and improve the quality of the compaction in the field, it is necessary to perform laboratory tests in order to determine material properties. A base course material 0/ 32 mm limestone from Gotland (Hejdeby) was investigated in this study. To determine properties of the material various laboratory tests such as proctor compaction test, Micro-Deval, Los Angeles, and grain distribution curve are conducted. To investigate how grain size distribution affects technical properties of the material, the 0/32 mm material was modified with two different samples; grain size distribution of 2/32 mm excluding superior material content, and 0+/32 mm with enhanced superior material content. The purpose of this study was to examine changes in material behavior during proctor compaction. Two aspects of changes in material behavior were emphasized in this study; the optimal water content and maximum dry density, as well as changes of both. As a reference for the limestone features, a traditional 0/32 mm tonalite material (granite) from Vällstaverket was used relating to proctor investigation. Material's resistance to abrasion and fragmentation was investigated by two methods: Micro-Deval and Los Angeles. The results were compared with other rock materials. Furthermore the bearing capacity of the material was verified by examination of the Young's modulus and degree of compaction, as well as properties of water content and dry density, at three trial areas on Gotland. This is performed with various methods such as static plate loading test, light weight deflectometer, density gauge/SDG200, and water/sand volume meter measurement test. By comparing results from different methods of measurement, it may indicate a relationship between these. Test area 3 consists of two smaller test areas which have different water content. The bearing capacity (Young's modulus) and the degree of compaction were measured after each roller passage. Different relationships were obtained between the amount of roller overpass, with Young's modulus of material; as well as degree of compaction. It was found in this study that limestone from Gotland (Hejdeby) maintain its position as construction material for the unbound layers of the road. The result from static plate load which indicated high E V2 values (Young's modulus) was obtained from the field, and it suggests that a fine bearing capacity can be achieved in the use of limestone.

How can a non-autonomous compaction roller be converted to become temporarily autonomous while it performs a 500hours endurance test? Particularlysince the compaction rollers in question is not built to be autonomous and shall not be autonomous after the endurance test is completed. The autonomous system shall also be adaptable to all compaction rollers which Dynapac is developing and shall be moved to another machine when the endurance test is completed. In this thesis a concept is engineered of how the whole autonomous system will work and a prototype is fabricated of how to convert the current manual mechanical steering to be performed by a computer. The steering prototype has been tested on a Dynapac CC4200 double drumasphalt compaction roller and worked as intended. To develop this, anextensive risk analysis is also established andwith it a requirements list of what's needed to be fulfilled when performing autonomous testing of a compaction roller. The work has been done using the method “design thinking” which is a collection of multiple methods to create new concepts and ideas. The final concept resulted in a navigation system which uses GNSS for path planning and limitation of the operation area. It also uses radar to detect foreign objects in its path to prevent a collision. Multiple systems arealso proposed to be used for malfunction detection of the roller, which is a major part of a human operator’sjob when testing out new machines. The test track for the machine was undefined and also hadto be engineeredas part of the concept. It resultedin closing the area of operation with a mesh fence to prevent access to the area from unauthorised personnel and geo-fence to prevent the machine from escaping. Access to the area is only granted to authorized personnel and only when the autonomous rolleris shut off. Due to the machines in question isn’t fully developed, theycan’t be trusted enough to have people inside the area of operation asthe autonomous machineis operating. / Hur kanen icke-autonom vägvältomvandlas tillatt bli tillfälligt autonom medan den utför ett 500timmar långttidsprov?Särskilt sedanvägvältenifrågainte ärbyggd för att vara autonom och ska intevara autonom efter attlångtidsprovetär slutfört. Det autonoma systemet skaävenkunna anpassas tillalla vältar som Dynapac utvecklar och ska flyttas till en annan maskin närlångtidsprovetär klart. Idenna avhandling konstrueras ett koncept för hur hela det autonoma systemet kommer att fungera ochenprototyp tillverkaspå hur man konverterar den nuvarande manuella mekaniska styrningen till attstyras av en dator. Styrprototypen testades på en Dynapac CC4200 asfaltsvält med dubbla valsar ochfungerade bra. En omfattande riskanalys utvecklades ochlika såen kravlista över vad som behöveruppnås vid autonom testning av en vägvält. Arbetet har gjorts med hjälp av metoden “designthinking”, vilket är en samling av flera metoder för att skapa nya koncept och idéer. Det slutgiltigakonceptet resulterade i ett navigationssystem som använder GNSS för navigering och begränsning avkörområdet. Den använder också radar för att upptäcka främmande föremål i sin vägvilketförhindrarkollision. Flera system föreslås användasförfunktionsfelsdetektering på välten, vilket är en viktig delav en mänskligoperatörs arbetevid provning av nya maskiner. Maskinen kommer att vara i ett slutetområde som är avskilt med ett nätstängsel.Tillträde till området ges endast till behörig personal ochendast när den autonoma välten är avstängd. På grund avmaskinerna ifråga inte är fullt utvecklade,kan de inte litas på tillräckligt för att ha personer inom körområdet medan det autonoma systemet är idrift.

A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles. Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced. Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. / QC 20100506

In der vorliegenden Arbeit wurden Experimente zur Fallgewichtsverdichtung in Modellversuchen im Erdschwerefeld (1g) durchgeführt. Ziel der Versuche war es, das Verformungsverhalten eines Versuchssandes in hoher räumlicher und zeitlicher Auflösung zu erfassen und Nachrechnungen im Sinne von Benchmark-Tests zu ermöglichen. Die messtechnische Erfassung des Bodenverhaltens erfolgte vor allem durch die optische Messmethode der digitalen Bildkorrelation (DIC, englisch: Digital Image Correlation). Ein wichtiger Teil der Arbeiten war in diesem Zusammen-hang die Eignungsprüfung der Messmethode an den eigenen Versuchsständen. Im Rahmen einer Variantenstudie mit 22 Modellkonfigurationen wurde zudem die Bedeutung von Steuergrößen der Fallgewichtsverdichtung hinter-fragt. Numerische Berechnungen wurden mit der Finite-Elemente-Methode (FEM) durchgeführt. Mit den Versuchen konnte Verschiebungen des Versuchssandes an der Sicht-ebene in hoher räumlicher Auflösung gemessen werden. Für die Erfassung bodendynamischer Vorgänge konnte die DIC-Auswertung von Hochge-schwindigkeitsaufnahmen sowie von Beschleunigungssensoren im Boden erfolgreich eingesetzt werden. Die DIC-Messung eines Granulats hinter einer transparenten Sichtebene führt zu einer Streuung der Verschiebungsergebnisse, was wiederum negative Auswirkung auf die Ermittlung von kleinräumigen Dehnungen hat. Eine besondere Herausforderung stellte in diesem Zu-sammenhang die Erfassung einer Änderung der Dichte bzw. Porenzahl über die naturgemäß kleinen Betragsänderungen der volumetrischen Dehnung dar. Das Verformungsverhalten des Versuchssandes zeigte bei der Fallgewichts-verdichtung große Ähnlichkeiten zu Versuchen mit statischer Auflast. Ergebnisse der Variantenstudie zeigen Zusammenhänge zwischen Steuergrößen der Fallgewichtsverdichtung und der Einflusstiefe auf. Es wird deutlich, dass die in der Baupraxis verbreitete Größe der potentiellen Fallenergie nur begrenzt für eine Klassifizierung von Fallgewichtskonfigurationen geeignet ist.:1 Einleitung 1 2 Zur praktischen Bedeutung der Fallgewichtsverdichtung 6 2.1 Geschichte der Verdichtung mit Fallgewichten 6 2.2 Anwendungsbereiche 6 2.3 Bodenmechanische Vorgänge während der Verdichtung 8 2.4 Wellenausbreitung bei impulsförmigem Energieeintrag 8 2.5 Bewertung des Verdichtungserfolges 9 3 Überblick zu experimentellen und rechnerischen Untersuchungen zur Fallgewichtsverdichtung 11 3.1 Feldversuche 11 3.2 Modellversuche 12 3.3 Berechnungsverfahren 29 4 Versuchstechnische Grundlagen 34 4.1 Geotechnische Experimente und deren Anforderung 34 4.2 Konzeption von Modellversuchen 35 4.3 Wahl und Realisierung von Randbedingungen 38 4.4 Erfassung und Auswertung von Messgrößen 38 4.5 Digital Image Correlation (DIC) 40 5 Versuchssand, Versuchsstände und Einbaumethoden 52 5.1 Versuchssand 52 5.2 Versuchsstand-C 54 5.3 Versuchsstand-S 57 5.4 Versuchsstand-M 61 5.5 Einbaumethoden 68 5.6 Kontrolle der Probenhomogenität 73 6 Versuche mit statischer Auflast 79 6.1 Versuchsprogramm und Ziele 79 6.2 Kompressionsversuche 81 6.3 Streifen- und Kreisfundamentversuche 93 6.4 Ergänzende Messungen 103 6.5 Zusammenfassung 106 7 Versuche mit skalierten Fallgewichten 108 7.1 Versuchsprogramm und Ziele 108 7.2 Fallgewichtsversuche im ebenen Verformungszustand 109 7.3 Fallgewichtsversuche als Halbmodell 115 7.4 Ergebnisse zusätzlicher Sondierungen 122 7.5 Ergänzende Messungen 125 7.6 Kinematik 130 7.7 Versuchsstudie zur Fallgewichtsverdichtung 133 7.8 Zusammenfassung 150 8 Vergleich zwischen statischen und dynamischen Versuchen 153 9 Numerische Berechnungen mit der Finite-Elemente-Methode 157 9.1 Grundlagen der verwendeten Finite-Elemente-Methode 157 9.2 Bestimmung der Stoffmodellparameter 160 9.3 Simulation der Kompressionsversuche 161 9.4 Simulation der Streifenfundamentversuche 170 9.5 Simulation der Fallgewichtsversuche 176 9.6 Kinematik 182 9.7 Zusammenfassung 186 10 Zusammenfassung 188 11 Ausblick Literaturverzeichnis 196 Anhang A Versuchsstudie zur Fallgewichtsverdichtung 204 A.1 Einzelversuche am Versuchsstand-S 204 A.2 Einzelversuche am Versuchsstand-M 208 Anhang B DIC-Studien an idealisiertem Versuchsaufbau 213 Anhang C Studie zu Zwischenbezugsschritten in ISTRA4D 220 Anhang D Studie zur Ermittlung von Dehnungen in ISTRA4D 223 Anhang E Kalibrierung der Stoffmodellparameter in Abaqus 227 Anhang F Hypoplastisches Stoffmodell ohne intergranulare Dehnung 229 Anhang G Hypoplastisches Stoffmodell mit intergranularer Dehnung 232 / A quantitative validation of numerical simulations of soil dynamic problems and the derivation of physical relationships needs appropriate experimental data. Within the scope of the present work, experiments on the heavy tamping in small-scaled models in earth's gravity (1g) were developed. The aim of the experiments was to record the deformation behavior of a test sand in high spatial and temporal resolution and to allow re-calculations in the sense of benchmark tests. The optical measuring method of digital image correlation (DIC) were mainly carried out for the metrological recording of the soil behavior. By comparing discrete image areas of a few grains of sand (patches), it is possible to full-field capture soil displacements behind a vertical viewing plane. In this context, an important part of the work was the suitability test of the measuring method at the own experiments. A variant study with 22 model configurations also questioned the importance of control factors of heavy tamping. The numerical calculations were performed with the finite element method (FEM) in Abaqus. Therefore, the simulation of individual special tests with static load were done using classical Lagrangian FEM. Experiments as well as with large soil deformations as well as heavy tamping were modeled using the Coupled Eulerian Lagrangian (CEL) method. As material model, a formulation of the hypoplasticity with extension to the concept of intergranular strains was used. The experiments showed that the optical measuring method of the DIC is capable of reliably detecting shifts of the test sand at the viewing plane in high spatial resolution. For the acquisition of soil dynamic processes, the DIC evaluation of high-speed recordings as well as of acceleration sensors in the soil could be successfully carried out. Experimental and metrological challenges resulted from the effects of optical refraction through the viewing plane as well as the detection and tracking of patterns of individual patches. In comparison to direct measurement on rigid bodies, the detection of a granulate behind a transparent viewing plane leads to a greater scattering of the displacement results, which in turn has a negative effect on the determination of small-scale strains in the measuring plane. A particular challenge in this context was the detection of a change in the density or pore number over the inherently small changes in the magnitude of the volumetric strain. Remarkably, the deformation behavior of the sand in medium-dense storage showed under the influence of falling-weight compacting great similarities to the deformation behavior under static loading. With both load models, the measurement results point to successful compaction work below and to the side of the load transfer, which are due to vertical or horizontal strain components. The results of the study on heavy tamping show correlations between the control factors of heavy tamping to an influence depth. The study shows that the size of the potential fall energy, which is common in construction practice, is only limitedly suitable for the classification of heavy tamping configurations. The evaluation of a series of drops proves the possibilities of correlation between state variables of a soil such as void ratio or degree of compaction and the velocity of the propagation waves in the soil. In numerical calculations, the deformation behavior of static load tests could be reproduced well. It showed the importance of a sufficient consideration of boundary conditions like friction between sand and container wall, container deformations and silo effects in narrow containers. Recalculations of the heavy tamping tests led to plausible results with a significant compaction effect below the drop weight, which is amplified in further drops and extended to greater depths. This also corresponds to the experimental results as well as the contexts known in practical engineering.:1 Einleitung 1 2 Zur praktischen Bedeutung der Fallgewichtsverdichtung 6 2.1 Geschichte der Verdichtung mit Fallgewichten 6 2.2 Anwendungsbereiche 6 2.3 Bodenmechanische Vorgänge während der Verdichtung 8 2.4 Wellenausbreitung bei impulsförmigem Energieeintrag 8 2.5 Bewertung des Verdichtungserfolges 9 3 Überblick zu experimentellen und rechnerischen Untersuchungen zur Fallgewichtsverdichtung 11 3.1 Feldversuche 11 3.2 Modellversuche 12 3.3 Berechnungsverfahren 29 4 Versuchstechnische Grundlagen 34 4.1 Geotechnische Experimente und deren Anforderung 34 4.2 Konzeption von Modellversuchen 35 4.3 Wahl und Realisierung von Randbedingungen 38 4.4 Erfassung und Auswertung von Messgrößen 38 4.5 Digital Image Correlation (DIC) 40 5 Versuchssand, Versuchsstände und Einbaumethoden 52 5.1 Versuchssand 52 5.2 Versuchsstand-C 54 5.3 Versuchsstand-S 57 5.4 Versuchsstand-M 61 5.5 Einbaumethoden 68 5.6 Kontrolle der Probenhomogenität 73 6 Versuche mit statischer Auflast 79 6.1 Versuchsprogramm und Ziele 79 6.2 Kompressionsversuche 81 6.3 Streifen- und Kreisfundamentversuche 93 6.4 Ergänzende Messungen 103 6.5 Zusammenfassung 106 7 Versuche mit skalierten Fallgewichten 108 7.1 Versuchsprogramm und Ziele 108 7.2 Fallgewichtsversuche im ebenen Verformungszustand 109 7.3 Fallgewichtsversuche als Halbmodell 115 7.4 Ergebnisse zusätzlicher Sondierungen 122 7.5 Ergänzende Messungen 125 7.6 Kinematik 130 7.7 Versuchsstudie zur Fallgewichtsverdichtung 133 7.8 Zusammenfassung 150 8 Vergleich zwischen statischen und dynamischen Versuchen 153 9 Numerische Berechnungen mit der Finite-Elemente-Methode 157 9.1 Grundlagen der verwendeten Finite-Elemente-Methode 157 9.2 Bestimmung der Stoffmodellparameter 160 9.3 Simulation der Kompressionsversuche 161 9.4 Simulation der Streifenfundamentversuche 170 9.5 Simulation der Fallgewichtsversuche 176 9.6 Kinematik 182 9.7 Zusammenfassung 186 10 Zusammenfassung 188 11 Ausblick Literaturverzeichnis 196 Anhang A Versuchsstudie zur Fallgewichtsverdichtung 204 A.1 Einzelversuche am Versuchsstand-S 204 A.2 Einzelversuche am Versuchsstand-M 208 Anhang B DIC-Studien an idealisiertem Versuchsaufbau 213 Anhang C Studie zu Zwischenbezugsschritten in ISTRA4D 220 Anhang D Studie zur Ermittlung von Dehnungen in ISTRA4D 223 Anhang E Kalibrierung der Stoffmodellparameter in Abaqus 227 Anhang F Hypoplastisches Stoffmodell ohne intergranulare Dehnung 229 Anhang G Hypoplastisches Stoffmodell mit intergranularer Dehnung 232

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Tire performance over soft soil influences the performance of off-road vehicles on soft soil, as the tire is the only force transmitting element between the off-road vehicles and soil during the vehicle operation. One aspect of the tire performance over soft soil is the tire tractive performance on soft soil, and it attracts the attention of vehicle and geotechnical engineers. The vehicle engineer is interested in the tire tractive performance on soft soil because it is related to vehicle mobility and energy efficiency; the geotechnical engineer is concerned about the soil compaction, brought about by the tire traffic, which accompanies the tire tractive performance on soft soil. In order to improve the vehicle mobility and energy efficiency over soft soil and mitigate the soil compaction, it's essential to develop an in-depth understanding of tire tractive performance on soft soil. This study has enhanced the understanding of tire tractive performance on soft soil and promoted the development of terramechanics and tire model parameterization method through experimental tests. The experimental tests consisted of static tire deflection tests, static tire-soil tests, soil properties tests, and dynamic tire-soil tests. The series of tests (test program) presented herein produced parameterization and validation data that can be used in tire off-road traction dynamics modeling and terramechanics modeling. The 225/60R16 97S Uniroyal (Michelin) Standard Reference Test Tire (SRTT) and loamy sand were chosen to be studied in the test program. The tests included the quantification or/and measurement of soil properties of the test soil, pre-traffic soil condition, the pressure distribution in the tire contact patch, tire off-road tractive performance, and post-traffic soil compaction. The influence of operational parameters, e.g., tire inflation pressure, tire normal load, tire slip ratio, initial soil compaction, or the number of passes, on the measurement data of tire performance parameters or soil response parameters was also analyzed. New methods of the rolling radius estimation for a tire on soft soil and of the 3-D rut reconstruction were developed. A multi-pass effect phenomenon, different from any previously observed phenomenon in the available existing literature, was discovered. The test data was fed into optimization programs for the parameterization of the Bekker's model, a modified Bekker's model, the Magic Formula tire model, and a bulk density estimation model. The modified Bekker's model accounts for the slip sinkage effect which the original Bekker's pressure-sinkage model doesn't. The Magic Formula tire model was adapted to account for the combined influence of tire inflation pressure and initial soil compaction on the tire tractive performance and validated by the test data. The parameterization methods presented herein are new effective terramechanics model parameterization methods, can capture tire-soil interaction which the conventional parameterization methods such as the plate-sinkage test and shear test (not using a tire as the shear tool) cannot sufficiently, and hence can be used to develop tire off-road dynamics models that are heavily based on terramechanics models. This study has been partially supported by the U.S. Army Engineer Research and Development Center (ERDC) and by the Terramechanics, Multibody, and Vehicle (TMVS) Laboratory at Virginia Tech. / Doctor of Philosophy / Big differences exist between a tire moving in on-road conditions, such as asphalt lanes, and a tire moving in off-road conditions, such as soft soil. For example, for passenger cars commonly driven on asphalt lanes, normally, the tire inflation pressure is suggested to be between 30 and 35 psi; very low inflation pressure is also not suggested. By contrast, for off-road vehicles operated on soft soil, low inflation pressure is recommended for their tires; the inflation pressure of a tractor tire can be as low as 12 psi, for the sake of low post-traffic soil compaction and better tire traction. Besides, unlike the research on tire on-road dynamics, the research on off-road dynamics is still immature, while the physics behind the off-road dynamics could be more complex than the on-road dynamics. In this dissertation, experimental tests were completed to study the factors influencing tire tractive performance and soil behavior, and model parameterization methods were developed for a better prediction of tire off-road dynamics models. Tire or vehicle manufacturers can use the research results or methods presented in this dissertation to offer suggestions for the tire or vehicle operation on soft soil in order to maximize the tractive performance and minimize the post-traffic soil compaction.

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 / Development of a virtual simulation model for the stone bed which forms the foundation of traditional rail track structures is discussed in this study for the purpose of improving a conventional railway maintenance practice called tamping. The stone bed, called ballast, is flexible and is susceptible to undesirable deformation due to the forces from train traffic on the rail tracks over their service time. Therefore, periodic restoration of track structure is performed by tamping to maintain the operational quality of the rail tracks and reduce the risk of train accidents. This simulation model is intended to accelerate the scientific development of the current tamping practices by providing unprecedented insight into the behavior of small stones which form the bulk of the ballast and obviating the requirement for costly physical experimentation. The nuances of the mechanical behavior of ballast have been examined by a comprehensive literature review and the selection of a modeling technique called Discrete Element Modeling (DEM) has been justified for modeling of ballast owing to its suitability in capturing intricate dynamics of ballast stones. The virtual simulation model which is developed as results of this work has been found to be extremely efficient in realistically predicting the outcome of tamping process for any set of conditions of interest. This implies that quality of the rail tracks after tamping can be studied for a variety of different test cases and most optimized set of tamping parameters which results in maximum track quality can be analyzed. However, it was observed that the accuracy of the results obtained from the simulation model is dependent on the level of detail which is used to input properties of the ballast into the model. Low level of detail results in less accurate results whereas a high level of detail takes an unreasonably long time to solve. Therefore, a compromise has to be made between accuracy and solution time while programming the simulation model, and additional work is required in the future to improve the solution speed of the model.