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  • 1.
    Yideti, Tatek Fekadu
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Packing theory-based Framework for Performance Evaluation of Unbound Granular Materials2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Enhancing the load bearing quality of granular layers is fundamental to optimize the structural performance of the pavements. Unbound granular materials are one of the most used materials in the base layers of pavements. There have been growing interests on the behavior of unbound granular material in road base layers. Both design of a new pavement and prediction of service life need proper characterization of unbound granular materials, which is one of the requirements for a new mechanistic pavement design methods.

    Adequate knowledge of the strength and deformation characteristics of unbound layers in pavements is essential for proper thickness design, residual life determination, and economic optimization of the pavement structure. The current knowledge concerning granular materials employed in pavement structures is limited. In addition, to date, no general framework has been established to explain and evaluate satisfactorily the behavior of unbound granular materials under the complex repeated loading which they experience.

    This thesis presents a packing theory-based framework to evaluate the mechanical properties of unbound granular materials. The framework was developed based on the particle-to-particle contact, the particle size distribution and the packing arrangement. The skeleton of the unbound materials should be composed of both coarse enough particles and a limited amount of fine granular materials to effectively resist deformation and carry traffic loads. Based on this, the framework identifies the two basic components of unbound granular materials, namely the primary structure (PS) - a range of interactive coarse grain sizes that forms the main load carrying network in granular materials and the secondary structure (SS) - a range of grain sizes smaller than the PS providing stability to the aggregate skeleton.

    In the framework, disruption potential (DP), PS porosity, PS coordination number and void ratio of skeleton (PS+SS) are among the key packing parameters which were established from the framework. These parameters were validated by evaluating the permanent deformation, resilient modulus and California bearing ratio of unbound granular materials using different materials with various experimental results.

    Furthermore, in this thesis a new moisture distribution model (Birgisson-Jelagin-Yideti (BJY) moisture distribution model) was introduced. In the model, SS particles associated with water retention. The water is stored as meniscus water between these small particles and fully filled in small voids. The volume of meniscus water between SS particles and the measured matric suction values are the two key parameters considered in the model. The results showed that the model developed is capable of predicting the experimentally measured matric suction values for a range of gradations.

    Finally, the application of shakedown and packing theories to characterize permanent deformation behaviour of unbound aggregate materials is presented. A simple finite element analysis has also been simulated in order to find out the effect of disruption potential on the shakedown limit load. Experimental results were used for the simulation of the finite element and compared favourably with the predicted mean stress and dimensionless shakedown load using DP values.

  • 2.
    Yideti, Tatek Fekadu
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Performance model for unbound grnular materials pavements2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Recently, there has been growing interest on the behaviour of unbound granular material in road base layers. Researchers have studied that the design of a new pavement and prediction of service life need proper characterization of unbound granular materials, which is one of the requirements for a new mechanistic design method in flexible pavement.

    Adequate knowledge of the strength and deformation characteristics of unbound layer in pavements is a prerequisite for proper thickness design, residual life determination, and overall economic optimization of the pavement structure. The current knowledge concerning the granular materials employed in pavement structures is limited. In addition, to date, no general framework has been established to explain satisfactorily the behaviour of unbound granular materials under the complex repeated loading which they experience.

    In this study, a conceptual method, packing theory-based model is introduced; this framework evaluates the stability and performance of granular materials based on their packing arrangement. In the framework two basic aggregate structures named as Primary Structure (PS), and Secondary Structure (SS). The Primary Structure (PS) is a range of interactive grain sizes that forms the network of unbound granular materials. The Secondary Structure (SS) includes granular materials smaller than the primary structure. The Secondary Structures fill the gaps between the particles in the Primary Structure and larger particles essentially float in the skeleton.

    In this particular packing theory-based model; the Primary Structure porosity, the average contact points (coordination number) of Primary Structure, and a new parameter named Disruption Potential are the key parameters that determine whether or not a particular gradation results in a suitable aggregate structure.

    Parameters mentioned above play major role in the aggregate skeleton to perform well in terms of resistance to permanent deformation as well as load carrying capacity (resilient modulus). The skeleton of the materials must be composed of both coarse enough and a limited amount of fine granular materials to effectively resist deformation and carry traffic loads.

  • 3.
    Yideti, Tatek Fekadu
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Jelagin, Denis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    A new moisture distribution model for unbound granular materialsIngår i: Geotechnique, ISSN 0016-8505, E-ISSN 1751-7656Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The presence of waterin the unbound granular materials significantly influences the mechanicalperformance of the material. The ability to estimate the soil watercharacteristic curve (SWCC) is crucial thus to determine the effect themoisture has on the mechanical behaviour of granular materials. In this paper,an analytical moisture distribution model is proposed. A packing theory-based framework to evaluateperformance of unbound granular materials reported previously by the authorsallows identifying the two basic components of the unbound granular materialsskeleton: primary structure (PS) - a range of interactive coarse grain sizes thatforms the main load carrying network in granular materials and secondarystructure (SS) - a range of grain sizes smaller than the PS providing stabilityto the aggregate skeleton. In the new moisture distribution model presented inthis paper, moisture wasconsidered to be stored as meniscus water between SS particles and water thatfilled in small voids.The volume of meniscus water between SS particles and the measured matricsuction values are the two key parameters in the model. In order to validatethe model predicted results are then compared with measuredmatric suction of granite granular materials with different gradations. Theresults showed that the model developed is capable of predicting theexperimentally measured matric suction values for a range of gradations. 

  • 4.
    Yideti, Tatek Fekadu
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Jelagin, Denis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Influence of aggregate packing structure on California bearing ratio values of unbound granular materials2014Ingår i: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 15, nr 1, s. 102-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Over the past several decades, California bearing ratio (CBR) value has been used in many countries for empirical pavement designs and still many countries are using it for unbound granular materials strength measurement and as input to their pavement design chart. Furthermore, CBR value of unbound granular material is frequently correlated with its fundamental mechanical properties such as resilient modulus, which in turn is often used as an input to a mechanistic pavement design procedure. In the present study, the effect the aggregate packing has on the CBR values of unbound materials is investigated. A packing theory-based framework that allows to identify the load-carrying part of the aggregate skeleton is presented. Aggregate packing parameters controlling the CBR performance of the unbound materials are introduced and evaluated with the experimentally measured CBR values of 20 unbound granular materials found in the literature. It is shown that the CBR values of granular materials are to a great extent controlled by the packing characteristics of their load-carrying skeleton.

  • 5.
    Yideti, Tatek Fekadu
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Jelagin, Denis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Guarin, Alvaro
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Packing theory-based framework for evaluating resilient modulus of unbound granular materials2014Ingår i: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 15, nr 8, s. 689-697Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Enhancing the quality of granular layers is fundamental to optimise the structural performance of the pavements. The objective of this study is to investigate whether previously developed packing theory-based aggregate parameters can evaluate the resilient modulus of unbound granular materials. In this study, 19 differently graded unbound granular materials from two countries (USA and Sweden) were evaluated. This study validated both porosity of primary structure (PS) and contact points per particle (coordination number) as key parameters for evaluating the resilient modulus of unbound granular materials. This study showed that decreasing the PS porosity - higher coordination number - calculated based on the proposed gradation model, yields higher resilient modulus. Good correlation was observed between the proposed packing parameters and resilient modulus of several types of aggregates. The packing theory-based framework successfully recognised granular materials that exhibited poor performance in terms of resilient modulus.

  • 6.
    Yideti, Tatek Fekadu
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Jelagin, Denis
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Guarin, Alvaro
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Packing theory-based framework to evaluate permanent deformation of unbound granular materials2013Ingår i: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 14, nr 3, s. 309-320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Permanent deformation of unbound granular materials plays an essential role in the long-term performance of a pavement structure. Stability of unbound granular materials is defined by the particle-to-particle contact of the system, the particle size distribution and the packing arrangement. This paper presents a gradation model based on packing theory to evaluate permanent deformation of unbound granular materials. The framework was evaluated by using 10 unbound granular materials from different countries. The disruption potential, which determines the ability of secondary structure (SS) to disrupt the primary structure (PS), is introduced. This study also identified the amount of PS and SS that may eventually be used as a design parameter for permanent deformation of unbound road layers. The evaluation of the model regarding permanent deformation behaviour of granular materials is found to compare favourably with experimental results.

  • 7.
    Yideti, Tatek Fekadu
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Dawson, Andrew
    The University of Nottingham.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Implementation of Shakedown and Packing theories for Unbound Granular materialsIngår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The shakedown theory is a tool to characterize the state of the structural system of an unbound granular material that is subjected to repeated loading when its response has become resilient in nature and no further accumulation of plastic strain occurs. This paper demonstrates the application of both shakedown and packing theories to characterize permanent deformation behaviour of unbound aggregate materials. Ranges of shakedown phenomenon (Ranges A, B and C) for some selected unbound materials have first been investigated based on their permanent strain responses. The disruption potential (DP) of the primary structure (PS) of the aggregate assemblage has then been determined for each grain size distribution based on a packing theory model. The DP was found to characterize satisfactorily the three types of shakedown ranges. A sensitivity analysis has also been done on DP values by changing the dry density and specific gravity, revealing the importance of these characteristics for shakedown. Further, a finite element analysis was performed to determine the shakedown limit load as a mean stress and a dimensionless shakedown load. The analysis was simulated using the Mohr-coulomb yield criteria for a three-dimensional cylindrical sample. From this study the DP value was found to compare favorably with the predicted mean stress and dimensionless shakedown load.

     

  • 8.
    Yideti, Tatek
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Jelagin, Denis
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Birgisson, Björn
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap.
    Moisture Distribution Model to Predict Matric Suction in Unbound Granular Materials as a Function of Fines Content2016Ingår i: TRB 95th Annual Meeting Compendium of Papers, 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The existence of water in the layers of unbound road aggregates significantly influences the performance of pavement structure. Thus, the ability to estimate volumetric water content and its capillary effect is very important. Several models have been suggested to link the matric suction of unbound materials to their water retention properties. In this paper, an analytical moisture distribution model is proposed by using packing theory-based framework for unbound granular materials. The framework was previously developed by the authors of this paper and identifies two basic components of unbound granular materials skeleton: primary structure (PS) - a range of interactive coarse grain sizes that forms the main load-carrying network in granular materials and secondary structure (SS) - a range of grain sizes smaller than the PS providing stability to the aggregate skeleton. In the new moisture model, water was considered to be stored as both menisci water between SS particles and water that fully filled in very small voids. In order to validate the model, predicted results are compared with measured matric suction of a granite material with different gradations. The results showed that the model is capable of predicting the experimentally measured matric suction values for a range of gradations.

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