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  • 1.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. Swedish National Road and Transport Research Institute, Sweden.
    Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test2017In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 18, no 1, p. 47-59Article in journal (Refereed)
    Abstract [en]

    This paper demonstrates the application of a generalised layered linear viscoelastic (LVE) analysis for estimating the structural response of flexible pavements. A comparison of the direct layered viscoelastic responses with approximate solutions based on the linear elastic (LE) and LVE collocation methods was also carried out. The different approaches were implemented by extending a layered elastic program with an improved computational performance. The LE and LVE collocation methods were further extended for analysis of pavements under moving loads. The methods were illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at pavement temperatures of 0, 10 and 20 degrees C, were measured using various types of sensors installed in the structure. It was shown that the approximated LVE solution based on the LE collocation method agreed very well with the measurements and is computationally the least expensive.

  • 2.
    Babiuc, Octavian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Effect of gritting sand quality on road dust pollution2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Pollution of air represents the contamination with matter that can affect both humanhealth and the environment. Road dust has been recognized as a dominant source ofparticulate matter and one of the factors that contributes to its development is the useof gritting sand. Gritting sand is being used during snowy winter conditions as atraction control method. During spring season, when snow and ice melt and surfacesdry out, and the influence of traffic, asphalt surface wear, particle ejection from tires,etc; under the effect of their interaction, cause the formation of particulate matter.A general aim of this study was to perform analysis of factors which can be consideredresponsible generating road pollution, with resistance to abrasion of gritting sandbeing a potential key problem. The correlation between the use of studded tires andparticulate matter formation has been considered to be one of major issues in urbanareas.In order to carry out this investigation, an individual study case was considered,measurements indicated that levels of pollution increased even after studded tires werebanned.The literature review revealed important knowledge gaps regarding the quantificationof particulate emissions from non-exhaust sources, most importantly, emissions due tolow quality gritting sanding. At this point, very little information is available thatcould be used for determining the resistance to abrasion of gritting sanding material.This is further supported by numerous institutions and companies, all suggesting thatquality of gritting sand is not taken into consideration. Gritting sand is part of abigger problem which also involves types of pavement, types of tires, weather,background pollution, etc. Furthermore, there is no practical method to characterizewear of resistance of gritting sand.

  • 3.
    Bekele, Abiy
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Rydén, Nils
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Gudmarsson, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Slow dynamic diagnosis of asphalt concrete specimen to determine level of damage caused by static low temperature conditioning2017In: 43rd Annual Review of Progress in Quantitative Nondestructive Evaluation, American Institute of Physics (AIP), 2017, Vol. 1806, article id 080012Conference paper (Refereed)
    Abstract [en]

    The phenomenon of slow dynamics has been observed in a variety of materials which are considered as relatively homogeneous that exhibit nonlinearity due to the presence of defects or cracks within them. Experimental realizations in previous work suggest that slow dynamics can be in response to acoustic drives with relatively larger amplitude as well as rapid change of temperature. Slow dynamics as a nonlinear elastic response of damaged materials is manifested as a sharp drop and then recovery of resonance frequency linearly with logarithmic time. In this work, slow dynamics recovery is intended to be used as a means of identifying and evaluating thermal damage on an asphalt concrete specimen. The experimental protocol for measuring slow dynamics is based on the technique of nonlinear resonance spectroscopy and is set up with non-contact excitation using a loud speaker and the data acquisition tool box of Matlab. Sweeps of frequency with low amplitude are applied in order to probe the specimen at its linear viscoelastic state. The drop and then recovery in fundamental axially symmetric resonance frequency is observed after the specimen is exposed to sudden temperature change. The investigation of the viscoelastic contribution to the change in resonance frequency and slow dynamics can help identify micro-damage in asphalt concrete samples.

  • 4.
    Bjurström, Henrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rydén, Nils
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Non-contact rolling surface wave measurements on asphalt concreteIn: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Other academic)
    Abstract [en]

    Rolling surface wave measurements on a single, thin asphalt concrete (AC) layer arepresented to investigate their use in rapid nondestructive field tests. An array of 47 micro-electromechanicalsensor (MEMS) microphones is mounted on a trailer together with an automated impactsource. Multichannel recordings from single impacts are obtained at 80 equally spaced positions as thetrailer moves at a constant speed. The complete battery-powered data acquisition system enables largescaletesting of newly built pavements. Multiple sets of test results show good repeatability for theassessed shear wave velocity and demonstrate the strong temperature dependency of AC. The presentedresults indicate a possible application for quality assurance of AC using rolling surface wavemeasurements.

  • 5.
    de Frias Lopez, Ricardo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ekblad, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    A Numerical Study on the Permanent Deformation of Gap-Graded Granular Mixtures2016In: Proceedings of the Third International Conference on Railway Technology: Research, Development and Maintenance / [ed] J. Pombo, Stirlingshire, UK: Civil-Comp Press , 2016Conference paper (Refereed)
    Abstract [en]

    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.

  • 6.
    de Frias Lopez, Ricardo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ekblad, Jonas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Resilient properties of binary granular mixtures: A numerical investigatio2016In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 76, p. 222-233Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    de Frias Lopez, Ricardo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Silfwerbrand, Johan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. School of Engineering and Applied Science, Aston University, Birmingham, UK.
    Force transmission and soil fabric of binary granular mixtures2016In: Geotechnique, ISSN 0016-8505, E-ISSN 1751-7656, Vol. 66, no 7, p. 578-583Article in journal (Refereed)
    Abstract [en]

    The effect of fines content on force transmission and fabric development of gap-graded mixtures under triaxial compression has been studied using the discrete-element method. Results were used to define load-bearing soil fabrics where the relative contributions of coarse and fine components are explicitly quantified in terms of force transmission. Comparison with previous findings suggests that lower particle size ratios result in higher interaction between components. A potential for instability was detected for underfilled fabrics in agreement with recent findings. It was also found that the threshold fines content provides an accurate macroscopic estimation of the transition between underfilled and overfilled fabrics.

  • 8.
    Onifade, Ibrahim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Dinegdae, Yared H.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Birgisson, Björn
    Hierarchical approach for fatigue cracking performance evaluation in asphalt pavements2017In: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 11, no 3, p. 257-269Article in journal (Refereed)
    Abstract [en]

    In this paper, a hierarchical approach is proposed for the evaluation of fatigue cracking in asphalt concrete pavements considering three different levels of complexities in the representation of the material behaviour, design parameters characterization and the determination of the pavement response as well as damage computation. Based on the developed hierarchical approach, three damage computation levels are identified and proposed. The levels of fatigue damage analysis provides pavement engineers a variety of tools that can be used for pavement analysis depending on the availability of data, required level of prediction accuracy and computational power at their disposal. The hierarchical approach also provides a systematic approach for the understanding of the fundamental mechanisms of pavement deterioration, the elimination of the empiricism associated with pavement design today and the transition towards the use of sound principles of mechanics in pavement analysis and design.

  • 9.
    Spross, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Olsson, Lars
    Geostatistik AB.
    Hintze, Staffan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Would risk management have helped? – A case study2015In: Geotechnical safety and risk V / [ed] T. Schweckendiek, A.F. van Tol, P. Pereboom, M.Th. van Staveren, P.M.C.B.M. Cools, Amsterdam: IOS Press, 2015Conference paper (Refereed)
    Abstract [en]

    To reduce the costs of unexpected geotechnical events in construction projects in Sweden, the Swedish Geotechnical Society has adopted a general methodology for risk management. In this paper, we exemplify how the proposed risk management philosophy could have been applied on a sheet-pile wall, which failed in 1992 in Stockholm because the design did not consider the complex site conditions. Focusing on the design phase, we discuss how geotechnical risks may be managed effectively as a natural part of the engineer’s everyday work.

1 - 9 of 9
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