| 1. |
- de Frias Lopez, Ricardo, et al.
(författare)
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A Numerical Study on the Permanent Deformation of Gap-Graded Granular Mixtures
- 2016
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Ingår i: Proceedings of the Third International Conference on Railway Technology. - Stirlingshire, UK : Civil-Comp Press.
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Konferensbidrag (refereegranskat)abstract
- Permanent deformation accumulation of unbound granular layers under traffic plays a critical role in the performance and need for maintenance of pavements and railway structures. In this paper, the discrete element method is used to study the permanent strain behaviour of binary mixtures of elastic spheres, as an idealization of gap-graded mixtures, under triaxial monotonic loading. The effects of stress level and soil fabric structure, based on a recently proposed classification system founded on micromechanical considerations, are assessed by subjecting mixtures with varying fines contents to different stress levels. Additionally, mixtures are loaded to static failure to study the dependency of the permanent strains on the closeness of the applied stress to failure stress, in accordance with existing empirical models. Numerical results are also compared with the experimentally determined behaviour of granular materials. The findings indicate that numerical mixtures are able to reproduce some of the most significant features observed in laboratory tests on granular materials, further encouraging the use of numerical simulations to enhance the understanding of granular media behaviour. Additionally, a good correlation between fabric structure and performance is obtained, giving additional support to the use of the studied fabric classification system for performance characterization.
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| 2. |
- de Frias Lopez, Ricardo
(författare)
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Granular Materials for Transport Infrastructures : Mechanical performance of coarse–fine mixtures for unbound layers through DEM analysis
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Granular materials are widely used as unbound layers within the infrastructure system playing a significant role on performance and maintenance. However, fields like pavement and railway engineering still heavily rely on empirically-based models owing to the complex behaviour of these materials, which partly stems from their discrete nature. In this sense, the discrete element method (DEM) presents a numerical alternative to study the behaviour of discrete systems with explicit consideration of the processes at particulate level governing the macroscopic response. This thesis aims at providing micromechanical insight into the effect of different particle sizes on the load-bearing structure of granular materials and its influence on the resilient modulus and permanent deformation response, both of which are greatly influenced by the stress level. In order to accomplish this, binary mixtures of elastic spheres under axisymmetric stress are studied using DEM as the simplest expression for gap-graded materials, which in turn also can be seen as a simplification of more complex mixtures.First, the effect of the fines content on the force transmission at contact level was studied. Results were used to define a soil fabric classification system where the roles of the coarse and fine fractions were defined and quantified in terms of force transmission.A behavioural correspondence between numerical mixtures and granular materials was established, where the mixtures were able to reproduce some of the most significant features regarding the resilient modulus and permanent strain dependency on stress level for granular materials.A good correlation between soil fabric and performance was also found. Generally, higher resilient modulus and lower deformation values were observed for interactive fabrics, whereas the opposite held for instable fabrics.Mixtures of elastic spheres are far from granular materials, where numerous additional factors should be considered. Nevertheless, it is the author’s belief that this work provides insight into the soil fabric structure and its effect on the macroscopic response of granular materials.
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| 3. |
- de Frias Lopez, Ricardo, et al.
(författare)
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Resilient properties of binary granular mixtures: A numerical investigatio
- 2016
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Ingår i: Computers and geotechnics. - : Elsevier. - 0266-352X .- 1873-7633. ; 76, s. 222-233
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Tidskriftsartikel (refereegranskat)abstract
- The effect of stress level on the resilient modulus for binary mixtures of elastic spheres under triaxial loading is investigated using the discrete element method. The secant modulus during the first cycle of unloading is used as an estimate of the modulus after several load cycles due to computational time restrains. Later in the paper, its adequacy as an accurate and efficient estimator is shown. Numerical results are statistically compared with existing relations characterizing the stress dependency of the resilient modulus for real granular materials. It is concluded that the modulus prediction is significantly improved considering the effect of the deviator stress in addition to the confinement stress, obtaining a good correlation between the modulus and the confinement to deviator stress ratio for the numerical mixtures. The stress dependency of a recently proposed soil fabric classification system, based on force transmission considerations at particulate level, is also studied and its correlation with performance investigated. It is found that the relative load-bearing role of coarse and fine components is governed by the deviator to confinement stress ratio. However, the implemented fabric classification is fairly insensitive to changes in this ratio. Regarding resilient performance, interactive fabrics show the stiffest response whereas underfilled fabrics should be avoided due to a potential for instability.
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| 4. |
- Edvardsson, Karin, et al.
(författare)
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Methods for Quantification of Lignosulphonate and Chloride in Gravel Wearing Courses
- 2010
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Ingår i: International Journal on Road Materials and Pavement Design. - 1468-0629 .- 2164-7402. ; 11:1, s. 171-185
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Tidskriftsartikel (refereegranskat)abstract
- Due to oxidation, breakdown, and leaching, dust suppressants will be lost from the gravel road surface. Methods for residual dust suppressant concentration supervision are a valuable tool for estimating life-length and optimal application rates, and, hence, efficiency of different products. The objective of this study was to identify methods for quantitative analyses of lignosulphonate and chloride, develop and adapt the methods for application on a gravel matrix, and validate the methods using samples collected in-situ. Results strongly suggest that the reliability and repeatability of the developed methods (23% for lignosulphonate and 30% for chloride, respectively) are acceptable for determination of relative variations in residual concentrations of dust suppressed gravel wearing courses.
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| 5. |
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| 6. |
- Ekblad, Jonas, et al.
(författare)
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Causes of rutting in flexible and semi-rigid test sections after 14 years of service
- 2018
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Ingår i: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 19:4, s. 878-897
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Tidskriftsartikel (refereegranskat)abstract
- Rutting is a major distress and is commonly targeted in design-build contracts as a key requirement, but at the same time, contemporary design methods usually provide scarce information on evolution in absolute terms. The objective of this paper is to investigate and analyse rutting results from a large full-scale road test. The analyses concerned magnitudes and the causes of rutting with a main focus on flexible and semi-rigid structures: one Reference, one high-performance asphalt (HPA) and one asphalt on a lean concrete (LC) base. Field measurements and sampling for the current study comprised acquiring transversal profiles and coring pavement samples. The results suggest that for the HPA and the LC base pavements, rutting is mainly caused by studded tyre wear and densification of the asphalt layers. For the conventional reference pavement additional rutting, most likely in the lower layers, was noted.
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| 7. |
- Ekblad, Jonas, et al.
(författare)
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Creep of prestressed sulphur concrete
- 1996
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Ingår i: Proceedings of the 7th International Conference on Durability of Building Materials and Components, 7DBMC. - Stockholm.
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Konferensbidrag (refereegranskat)
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| 8. |
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| 9. |
- Ekblad, Jonas, et al.
(författare)
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Impact on rutting from introduction of increased axle loads in Finland
- 2020
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Ingår i: The international journal of pavement engineering. - : Taylor and Francis Ltd.. - 1029-8436 .- 1477-268X.
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, Finland introduced legislation increasing gross vehicle weights (GVW) on a number of trucks. Since the actual impact on road damage is nearly impossible to quantify in advance, the present analysis of road surface measurements is intended to provide knowledge regarding the impact on road damage. Rutting is influenced by many conflated phenomena. To indicate and capture the effect on road damage due to the new maximum GVW for certain truck- and trailer combinations, the analysis follows two different but mutually supporting lines of reasoning, empirical and theoretical, respectively. Analysis of measured rut depth is supported by theoretical calculations. Theoretical findings clearly indicate that the relative increase in road damage induced by higher GVW is larger than the increase in relative payload capacity. There was a rapid fleet shift towards heavier trucks after 2013, and statistical (empirical) analysis of road surface measurements shows an increase in rutting after this introduction.
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| 10. |
- Ekblad, Jonas, et al.
(författare)
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Influence of mica content on time domain reflectometry and soil-water characteristic curve of coarse granular materials
- 2008
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Ingår i: ASTM geotechnical testing journal. - 0149-6115 .- 1945-7545. ; 31:4, s. 321-333
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Tidskriftsartikel (refereegranskat)abstract
- Elevated fractions of free mica particles in unbound granular materials, used in road constructions, are believed to reduce bearing capacity and influence the hydraulic behavior of the road structure. The objective of this investigation was to study the influence of mica content on the soil water characteristic curve and the dielectric response measured by time domain reflectometry, for coarse granular (maximum particle size 63 mm) materials. Increased fraction of mica was achieved by partly replacing the base crushed rock material smaller than 4 mm, by pure muscovite mica of similar grading, thereby keeping the overall particle size distribution unchanged. Acquired results indicated that, given equal matric suction, the water retention capacity increased with increased amount of mica. Concerning the time domain reflectometry measurements, no influence of mica content could be detected. Determined water contents required adjustment because of the nonlinear distribution of water in the sample.
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