Eyal Levenberg
Technical University of Denmark (DTU), Civil Engineering, Faculty Member
- Pavement Engineering, Pavement Materials, Flexible Pavement Design, Geotechnical Engineering, Asphalt Pavements, Inertial Sensors, and 10 moreTriaxial testing, Inverse Problems In Engineering, Viscoelasticity, Nonlinear Viscoelasticity, Viscoplasticity, Damage Mechanics, Soil Mechanics, Magic, Fencing, and Swimmingedit
- Open to collaborationedit
Research Interests:
Research Interests:
This study was motivated by the desire to provide highway managers/operators with more frequent and spatially dense information about the prevailing friction conditions in their networks. A new data-driven method was outlined for this... more
This study was motivated by the desire to provide highway managers/operators with more frequent and spatially dense information about the prevailing friction conditions in their networks. A new data-driven method was outlined for this purpose, wherein the prevailing tire–pavement grip potential is estimated from vehicle vibrations recorded during normal/regular usage of the infrastructure. The method was based on the underlying premise that transverse vehicle accelerations are related to wheel side-force oscillations, and therefore carry information related to the ride surface texture. It involved performing a short-time Fourier transform over vibration signals and analyzing the resulting spectral amplitudes. Two field experiments were carried out to validate the method. The first provided evidence of a statistical link between transverse vehicle vibrations and wheel side-force oscillations. The second tested the statistical link between skid resistance measured over a 26 km highway section and corresponding skid resistance estimations based on vehicle vibration data. Overall, transverse vehicle vibration characteristics were found to hold relevant information about the prevailing tire–pavement grip potential; the two were moderately inter-correlated. The newly proposed estimation method seems promising and potentially useful for pavement management applications, especially when considering the emergence of connected car technologies and the increased availability (and affordability) of in-vehicle Internet of Things devices.
Research Interests:
This paper is concerned with electrically heated asphalt pavements; it numerically explores the possibility of such technology to actively suppress frost penetration under seasonal cold-weather conditions. A thermal model is outlined for... more
This paper is concerned with electrically heated asphalt pavements; it numerically explores the possibility of such technology to actively suppress frost penetration under seasonal cold-weather conditions. A thermal model is outlined for the investigation based on the one-dimensional heat equation including latent heat effects. This model is applied to a multilayer medium containing a buried heat source representing the heating system. Utilizing cold-climate weather data from northern Finland, calculations were performed to track the evolution of the frost front depth in an idealized pavement structure with no heating. Then the model calculations were repeated with the heating activated. A parametric study was performed with different heat production intensities and several embedment depths for the heating system. It is numerically demonstrated that embedded electrical heating can suppress frost penetration depth and duration in asphalt pavements, rendering the explored application practically feasible.
Research Interests:
This study was motivated by the need for a mechanistic-empirical (ME) design method applicable to asphalt pavements after mill-and-overlay repairs that include reinforcing grids; the focus was solely on the mechanistic component. A new... more
This study was motivated by the need for a mechanistic-empirical (ME) design method applicable to asphalt pavements after mill-and-overlay repairs that include reinforcing grids; the focus was solely on the mechanistic component. A new model, based on layered theory, was developed – coupling in one single framework the following features: elastic layers for representing subgrade and unbound layers, fragmented layers for representing existing aged and densely cracked asphalt concrete (AC), imperfect bonding conditions for representing any differential slippage between adjoining layers, thermo-viscoelastic layer properties for representing new AC, and moving loads for representing traffic conditions. Grid effects were modelled as a combination of three contributions: the presence of an additional thin high-modulus elastic layer within the pavement system, the influence of a grid on interlayer bonding between layer above and below it, and the influence of a grid on the properties of the surrounding AC. These contributions require new grid-related modelling inputs that are physically meaningful and generic – not limited to any specific product. A secondary objective of the work was to generate some initial intuition on the mechanistic effects of interlayer grids. Accordingly, the new model was demonstrated in a parametric investigation covering a synthetic milled-and-overlaid structure with and without reinforcement. Findings from this demonstration provided an initial validation for the new model, given the conformity to findings from experimental studies. Overall, the new model is deemed a candidate computational engine for a ME design applicable to new and rehabilitated asphalt pavement systems. Furthermore, it can serve as an analysis tool to guide manufacturers on improving their products or showcasing existing capabilities in a quantified manner. Lastly, the new model can support the design of experimental setups for assessing grid effects within asphalt pavement systems, and therefore ensure the collection of usable measurements for subsequent mechanistic interpretation.
Research Interests:
Modern cars are equipped with many sensors that measure information about the vehicle and its surroundings. These measurements are therefore related to the ride-surface conditions over which the vehicle is passing. The paper commences by... more
Modern cars are equipped with many sensors that measure information about the vehicle and its surroundings. These measurements are therefore related to the ride-surface conditions over which the vehicle is passing. The paper commences by outlining a four-component vision for performing road condition evaluation based on in-vehicle sensor readings and subsequent feeding of pavement management systems (PMSs) with live condition information. This is expected to enrich the functionalities of PMSs, and ultimately lead to improved maintenance and repair decisions. Next the LiRA (Live Road Assessment) project—an ongoing proof-of-concept attempt to realize the vision components—is presented. The project elements and software architecture are described in detail, listing any assumptions, compromises, and challenges. LiRA involves a fleet of 400 electric cars operating in Copenhagen, both within the city streets and nearby highways. Sensor data collection is performed with a customized Internet of Things (IoT) device installed in the cars. Data processing and structuring involve new software tools for quality control, spatio-temporal interpolation, and map matching. A hybrid approach, combining machine learning models with physical (mechanics-based) models, is currently being applied to convert data into relevant information for PMSs. Based on the experience thus far with LiRA, the vision actualization is deemed achievable, workable, and upscalable.
Research Interests:
A 3D mechanical model of a ballastless asphalt track mockup was developed within the general-purpose finite element software ABAQUS. The mockup (and model) consisted of three wide-base sleepers equipped with a geotextile at the bottom,... more
A 3D mechanical model of a ballastless asphalt track mockup was developed within the general-purpose finite element software ABAQUS. The mockup (and model) consisted of three wide-base sleepers equipped with a geotextile at the bottom, supported on an asphalt pavement structure encapsulated in a large rigid box. The asphalt layer was modeled as linear viscoelastic; the underlying unbound granular layer was treated as stress-dependent nonlinear-elastic, implemented via a user-defined subroutine. The vast majority of model parameters were calibrated through laboratory element tests, while the remaining parameter values were based on technical literature or material specifications; only very few were calibrated using experimental data from the mockup itself. Implicit dynamic analysis was carried out under a loading history that simulated a train passage by sequentially exciting the three sleepers with a time delay. Vertical stresses at the bottom of the unbound granular layer, horizontal strains at the bottom of the asphalt layer, vertical accelerations at the track surface, and relative displacements at different locations were numerically evaluated. Subsequently, model predictions were validated by comparison against corresponding response-traces measured in the mockup. Overall, the predicted responses were in very good agreement with the experimental measurements. The peak vertical stresses below the unbound granular layer were moderately overestimated, while the peak horizontal asphalt strains were underestimated. In particular, the characteristic shape-features recorded by the stress and strain sensors at multiple locations in the mockup could be replicated. Pearson’s correlation coefficients between measured and calculated response histories for stresses and strains were higher than 0.96. Predicted and measured vertical accelerations were of the same order of magnitude, and their corresponding frequency spectra exhibited a correlation value greater than 0.97. The validated model has verified that during a simulated train passage, the substructure of a ballastless track mockup experiences low-magnitude vertical deformations, 77% of which develop in the rail pad, 15% in the geotextile, and 6% within the unbound granular layer. Moreover, the peak vertical stress in the unbound granular layer (33 kPa) and the peak horizontal tensile strain in the asphalt layer (18με) are lower than limiting design values.
Research Interests:
Layered elastic theory is a familiar and commonly accepted framework for modelling and analysis of pavement systems. In actuality however, the suitability of the theory is challenged whenever the system includes a fragmented layer – which... more
Layered elastic theory is a familiar and commonly accepted framework for modelling and analysis of pavement systems. In actuality however, the suitability of the theory is challenged whenever the system includes a fragmented layer – which violates the inherent layer continuity assumption. This paper addressed the modelling challenge in these situations by introducing a fragmented layer into the accepted framework. A new formulation was proposed, based on the hypothesis that the thickness of the fragmented layer can be incorporated as part of its governing parameters. Doing so allowed for treating the fragmented layer as a new kind of interface. Subsequently, the work focused on formulation development and clear step-by-step presentation of new derived expressions applicable to the case of a stratified half-space containing a fragmented layer. Several synthetic cases were generated and interrogated to verify the correctness of underlying equations and to demonstrate capabilities. Based on this interrogation the proposed formulation is deemed rich of prospective utility, especially for modelling pavements surfaced with concrete paving blocks, pavement systems that contain cracked-and-seated (or rubblised) Portland cement concrete, and aged or rehabilitated pavement systems that contain fatigued (multi-fractured) asphalt concrete layers.
Research Interests:
In recent years, there has been renewed interest in developing Moving Measurement Platforms (MMPs) to replace the Falling Weight Deflectometer (FWD) which currently serves as the industry standard for project-level pavement evaluation.... more
In recent years, there has been renewed interest in developing Moving Measurement Platforms (MMPs) to replace the Falling Weight Deflectometer (FWD) which currently serves as the industry standard for project-level pavement evaluation. The purpose of this study was to contribute to the transition efforts from FWD to MMPs. While focusing on a new MMP device (called Raptor) based on line profile sensing technology, the work addressed three fundamental aspects needed for eventual field data assessment and industry acceptance: (i) Loading and measurement setup – presenting an innovative device consisting of a beam equipped with several line profilers and also motion tracking sensors. By means of image analysis, this configuration allows for tracking a point on the pavement surface and measuring displacement information while moving. (ii) Interpretation method – capable of accepting device-measured data as input, and providing elastic properties for a layered pavement model. (iii) Sensitivity to measurement errors – where the interpretation method is first validated and then interrogated for error effects on the inferred moduli. Overall, the obtained results provide basic confidence in the device and the interpretation method, and demonstrate that the technology has the potential to meet project-level pavement evaluation needs.
Research Interests:
One of the problems affecting mature hydrocarbon fields, e.g., Ekofisk, Tyra, and Dan in the North Sea, is seabed subsidence due to reservoir depletion. Fluid injection is a widely used method to boost production and/or maintain reservoir... more
One of the problems affecting mature hydrocarbon fields, e.g., Ekofisk, Tyra, and Dan in the North Sea, is seabed subsidence due to reservoir depletion. Fluid injection is a widely used method to boost production and/or maintain reservoir pressure in order to mitigate compaction and subsidence. Both reservoir depletion and fluid injection operations might induce seabed deformations. The deformation pattern potentially holds useful information about production efficiency and reservoir management, which could be captured by careful monitoring of seabed strains. Therefore, the idea suggested herein was performing near full-field and continuous monitoring of seabed deformations by means of distributed fibre-optic strain sensing. The objective of the study was to theoretically calculate and assess whether current technologies (i.e., off-the-shelf optical interrogators) are accurate and sensitive enough to detect production-induced seabed strains originating at a 2 km-deep reservoir. The analysis indicates that depletion-induced subsidence is potentially measurable with seabed distributed fibre-optic strain sensing. However, the operation of an injector-producer array induces seabed strains that are too small to be detected with current capabilities.
Research Interests:
The reversible mechanical behavior of unbound granular layers (UGLs) is commonly characterized by a stress-state dependent resilient modulus. This paper investigated the dependency of in situ resilient modulus upon a change in temperature... more
The reversible mechanical behavior of unbound granular layers (UGLs) is commonly characterized by a stress-state dependent resilient modulus. This paper investigated the dependency of in situ resilient modulus upon a change in temperature above freezing conditions, i.e., the thermal sensitivity of UGLs in pavement systems excluding frost action. Such sensitivity is usually ignored in design and analysis because, on a material level, resilient modulus parameters are temperature independent. A model was developed to analyze this dependency by considering the stress -state changes that arise when UGLs are suppressed from thermally expanding or contracting. The formulation was incremental, based on linear thermoelasticity equations, and required as input readily available information; it assumed that changing temperature conditions are exogenous to the model and that no external loads are applied. A transcendental equation was subsequently derived, from which the sought sensitivity of UGLs could be resolved and quantified. Based on a parametric investigation of the model, covering a wide range of representative parameters, it is concluded that UGLs exhibit non -negligible thermal sensitivity. The extent of the calculated sensitivity coincides with field observations based on deflection testing, and also with seasonal factors that are traditionally applied to adjust field-measured moduli. Ultimately, the study shows that resilient modulus of UGLs is governed by an initial stress-state that is associated with a certain reference temperature level, and also by the temperature change compared to the reference.
Research Interests:
The evaluation of soil reaction in geotechnical foundation systems such as concrete pavements, mat-and raft foundations is a challenging task, as the process involves both the selection of a representative mechanical model (e.g., Winkler,... more
The evaluation of soil reaction in geotechnical foundation systems such as concrete pavements, mat-and raft foundations is a challenging task, as the process involves both the selection of a representative mechanical model (e.g., Winkler, Continuum, Pasternak, etc.) and identify its prevailing parameters. Moreover, the support characteristics may change with time and environmental situation. This paper presents a new method for the characterization of plate foundation support using high-resolution fiber-optic distributed strain sensing. The approach involves tracking the location of distinct points of zero and maximum strains, and relating the shift in their location to the changes in soil reaction. The approach may allow the determination of the most suited mechanical model of soil representation as well as model parameters. Routine monitoring using this approach may help to asses the degradation of the subsoil with time as part of structural health monitoring strategies. In this paper, fundamental expressions that relate between the location of distinct strain points and the variation of soil parameters were developed based on various analytical foundation support models. Finally, as an initial validation step and to underpin the idea basics, the proposed method was successfully demonstrated on a simple mechanical setup. It is shown that the approach allows for load-independent characterization of the soil response and, in that sense, it is superior to common identification methods.
Research Interests:
This work contributed an analytical quasistatic solution to the problem of an infinite viscoelastic plate supported on a Pasternak foundation and subjected to axisymmetric normal loading. The derivation was based on defining a set of... more
This work contributed an analytical quasistatic solution to the problem of an infinite viscoelastic plate supported on a Pasternak foundation and subjected to axisymmetric normal loading. The derivation was based on defining a set of iterative functions, each containing information on the plate’s relaxation modulus and on the time-variation of the loading. By writing the sought solution as a linear combination of these functions it was shown how to decompose the original viscoelastic problem into a set of independent elastic plate problems for which analytical solutions exist. Thus, the plate’s deflection evolution at any point of interest was provided in closed-form, without resorting to integral transform techniques. The formulation was applied and subsequently validated for several test cases, demonstrating that a very small set of elastic solutions is needed for generating a highly accurate viscoelastic result. Overall, the proposed solution is deemed well suited for engineering calculations, as a computational kernel for backcalculation, and for benchmarking numerical solutions.
Research Interests:
In situ evaluation of mechanical pavement properties requires fitting measured surface displacements with model displacements. Such inverse analysis is guided by optimisation algorithms that entail re-execution of the underlying model... more
In situ evaluation of mechanical pavement properties requires fitting measured surface displacements with model displacements. Such inverse analysis is guided by optimisation algorithms that entail re-execution of the underlying model many times over. For layered elasticity, which is the most commonly employed pavement model, this involves calculating computationally demanding semi-infinite integrals in every optimisation step. In this connection, a method was proposed to improve the computational efficiency of surface displacement recalculations in layered elastic systems. It was based on manipulating the original integrals by adding and then subtracting carefully selected auxiliary functions so that they remained mathematically unchanged, yet became faster to compute. The auxiliary functions were derived from an analytic interrogation, rendering the formulation robust and applicable to any layered elastic system without practical restrictions on the model parameters. Overall, the method is deemed consistently more efficient than standard evaluation techniques for achieving a given accuracy level.
Research Interests:
In recent years the pavement engineering community has shown increasing interest in shifting from a stationary falling weight deflectometer (FWD) to moving testing platforms such as the traffic speed deflectometer (TSD). This paper dealt... more
In recent years the pavement engineering community has shown increasing interest in shifting from a stationary falling weight deflectometer (FWD) to moving testing platforms such as the traffic speed deflectometer (TSD). This paper dealt with comparing TSD measurements against FWD measurements; it focused on the comparison methodology, utilizing experimental data for demonstration. To better account for differences in loading conditions between the two devices a new FWD deflection index was formulated first. This index served as reference/benchmark for assessing the corresponding TSD measurements. Next, a Taylor diagram was proposed for visualizing several comparison statistics. Finally, a modern agreement metric was identified and applied for ranking comparison results across different datasets. Overall, the suggested methodology is deemed generic and highly applicable to future situations, especially for assessing the worth of emerging device upgrades or improved interpretation schemes (or both).
Research Interests:
Structural health monitoring is a critical requirement in many composites. Numerous monitoring strategies rely on measurements of temperature or strain (or both), however these are often restricted to point-sensing or to the coverage of... more
Structural health monitoring is a critical requirement in many composites. Numerous monitoring strategies rely on measurements of temperature or strain (or both), however these are often restricted to point-sensing or to the coverage of small areas. Spatially-continuous data can be obtained with optical fiber sensors. In this work, we report high-resolution distributed Brillouin sensing over standard fibers that are embedded in composite structures. A phase-coded, Brillouin optical correlation domain analysis (B-OCDA) protocol was employed, with spatial resolution of 2 cm and sensitivity of 1 • K or 20 micro-strain. A portable measurement setup was designed and assembled on the premises of a composite structures manufacturer. The setup was successfully utilized in several structural health monitoring scenarios: (a) monitoring the production and curing of a composite beam over 60 h; (b) estimating the stiffness and Young's modulus of a composite beam; and (c) distributed strain measurements across the surfaces of a model wing of an unmanned aerial vehicle. The measurements are supported by the predictions of structural analysis calculations. The results illustrate the potential added values of high-resolution, distributed Brillouin sensing in the structural health monitoring of composites.
Research Interests:
This paper focused attention to the falling weight deflectometer (FWD) load-time history. For a commonly used device, it studied the pulse generation mechanism and the influence of different load histories on backcalculation results. In... more
This paper focused attention to the falling weight deflectometer (FWD) load-time history. For a commonly used device, it studied the pulse generation mechanism and the influence of different load histories on backcalculation results. In this connection, a semi-analytic impact theory was first introduced for realistically simulating FWD pulse generation. Then a newly developed finite-element code was presented for FWD interpretation; the code is capable of addressing dynamics, time-dependent layer properties, and quasi-nonlinear behavior. Both new developments were demonstrated for an experimental dataset that resulted from operating an FWD with different loading configurations. It was found that backcalculated parameters are sensitive to the FWD pulse features. Consequently, it is recommended that, whenever advanced pavement characterization is sought, experimental attention should be placed on generating diverse FWD pulse histories. Collectively, the resulting deflection histories will contain pertinent constitutive information for supporting the calibration of more complex pavement models.
Research Interests:
This paper deals with quantifying the resilience of a network of pavements. Calculations were carried out by modeling network performance under a set of possible damage–meteorological scenarios with known probability of occurrence.... more
This paper deals with quantifying the resilience of a network of pavements. Calculations were carried out by modeling network performance under a set of possible damage–meteorological scenarios with known probability of occurrence. Resilience evaluation was performed a priori while accounting for optimal preparedness decisions and additional response actions that can be taken under each of the scenarios. Unlike the common assumption that the pre-event condition of all system components is uniform, fixed, and pristine, component condition evolution was incorporated herein. For this purpose, the health of the individual system components immediately prior to hazard event impact, under all considered scenarios, was associated with a serviceability rating. This rating was projected to reflect both natural deterioration and any intermittent improvements due to maintenance. The scheme was demonstrated for a hypothetical case study involving LaGuardia Airport. Results show that resilience can be impacted by the condition of the infrastructure elements, their natural deterioration processes, and prevailing maintenance plans. The findings imply that, in general, upper bound values are reported in ordinary resilience work, and that including evolving component conditions is of value.
Research Interests:
This paper explores the possibility of using high-resolution fiber-optic distributed sensing for in situ geotechnical estimation of soil shear modulus distribution with depth. It is shown that a recursive analysis of an elastic problem... more
This paper explores the possibility of using high-resolution fiber-optic distributed sensing for in situ geotechnical estimation of soil shear modulus distribution with depth. It is shown that a recursive analysis of an elastic problem together with a measured vertical strain can assist in evaluating the sought stiffness values. It is suggested that high-resolution fiber-optic distributed sensing can provide the necessary strain for the proposed process. The approach was demonstrated in a field trial, entailing a stratified soil profile including a thin sand layer encapsulated between two clay layers. Results of the suggested profiling method are compared against data from a geophysical survey and against correlations with conventional in situ testing. Excellent agreement is exhibited between the different methods, indicating aptitude and viability of the idea for implementation as a geotechnical investigative tool.
Research Interests:
This paper models and analyzes a pavement’s response to a passing vehicle as captured by an embedded inertial sensor. Both ideal conditions, in which the riding surface is perfectly smooth, and more realistic conditions, in which load... more
This paper models and analyzes a pavement’s response to a passing vehicle as captured by an embedded inertial sensor. Both ideal conditions, in which the riding surface is perfectly smooth, and more realistic conditions, in which load magnitudes fluctuate, are considered. A new backcalculation scheme is proposed for the use of a measured acceleration trace as the basis for inferring mechanical layer properties, vehicle travel speed, and weight distribution between axles. The suggested approach does not require double integration of the raw signal to arrive at displacements; this approach is based on matching computed accelerations with smoothed field measurements. The overall performance of the method is validated by application to several synthetic cases and to field-measured data.
Research Interests:
The behavior under load of asphalt concrete (AC) was viewed as additively separable into viscoelastic and viscoplastic components, and the study focused on modeling the pre-peak response of the viscoelastic part under constant temperature... more
The behavior under load of asphalt concrete (AC) was viewed as additively separable into viscoelastic and viscoplastic components, and the study focused on modeling the pre-peak response of the viscoelastic part under constant temperature conditions. Non-linear viscoelastic behavior was first exposed in
several test modes, and a constitutive theory was subsequently offered – potentially capable of capturing and reproducing the observations. The modeling was based on replacing applied stresses in the linear convolution formulation with effective stresses; it included a mechanism for simulating the following
effects: (i) short-lasting damage, (ii) long-lasting damage, (iii) stiffening under compressive conditions and (iv) healing during recovery intervals. As an initial validation effort, the model’s reproducibility was assessed by calibration to a uniaxial compression experiment consisting of both small and medium strain levels. Next, the calibrated model was employed to forecast small-strain behavior in a standard complex modulus test. The simulated results qualitatively agree with recently reported findings that challenge the existence of a linear viscoelastic domain for AC.
several test modes, and a constitutive theory was subsequently offered – potentially capable of capturing and reproducing the observations. The modeling was based on replacing applied stresses in the linear convolution formulation with effective stresses; it included a mechanism for simulating the following
effects: (i) short-lasting damage, (ii) long-lasting damage, (iii) stiffening under compressive conditions and (iv) healing during recovery intervals. As an initial validation effort, the model’s reproducibility was assessed by calibration to a uniaxial compression experiment consisting of both small and medium strain levels. Next, the calibrated model was employed to forecast small-strain behavior in a standard complex modulus test. The simulated results qualitatively agree with recently reported findings that challenge the existence of a linear viscoelastic domain for AC.
Research Interests:
This work focuses on improving the linear viscoelastic characterization of asphalt concrete materials with a standard indirect tension setup. Three main aspects distinguish this investigation from typical efforts. First, the applied... more
This work focuses on improving the linear viscoelastic characterization of asphalt concrete materials with a standard indirect tension setup. Three main aspects distinguish this investigation from typical efforts. First, the applied diametral force history consisted of load–unload–rest sequences; this was done to enable separation between recoverable and irrecoverable deformation components. Second, viscoelastic properties were essentially calibrated against the recoverable deformation part to guarantee agreement with the sought constitutive theory; response during rest intervals was modeled for this purpose, assuming inactivity of the irrecoverable deformation part. Third, diametral forces were alternated between tension and compression; this was done to restrain the accumulation of irrecoverable deformation and to widen the calibration domain. Detailed step-by-step guidelines are included and applied to clarify the approach. For pavement
engineering purposes, the overall scheme is deemed an improvement over common or existing methods.
engineering purposes, the overall scheme is deemed an improvement over common or existing methods.
Research Interests:
Pavements resting on active clays are exposed to uneven heaving and shrinking of their bottom boundary. This paper investigated the inherent ability of pavements to mitigate such underlying (core) roughness. The problem is addressed and... more
Pavements resting on active clays are exposed to uneven heaving and shrinking of their bottom boundary. This paper investigated the inherent ability of pavements to mitigate such underlying (core) roughness. The problem is addressed and analyzed with an analytic model. It is found that the combined thicknesses of all inert pavement layers govern this smoothing feature. Core wavelengths that are much larger compared to the aforementioned thickness are essentially mirrored at the surface. Conversely, core wavelengths shorter than the system’s thickness are attenuated. The information included in this work can serve as an additional (and rational) decision basis for the design and evaluation of pavements on expansive soils.
A new one-dimensional viscoelastic creep formulation is proposed for modeling the recoverable deformation component in asphalt concrete. The formulation is designed to accommodate different tensile and compressive properties in analogy... more
A new one-dimensional viscoelastic creep formulation is proposed for modeling the recoverable deformation component in asphalt concrete. The formulation is designed to accommodate different tensile and compressive properties in analogy with bimodular elasticity. It is structured as a Volterra equation of the second kind with a kernel that alternates between tensile and compressive compliances based on the sign of the viscoelastic strain. If the response is only in one direction, or if the viscoelastic properties are identical in both directions, the model degenerates to the linear Boltzmann superposition. As a demonstrative application, the theory was utilized to match the response of an asphalt specimen exposed to several load-unload-rest sequences in uniaxial tension-compression. It was found that two dissimilar creep functions were needed to achieve excellent reproducibility. At short times the two were almost overlapping while for longer times they departed such that the compliance associated with compression was lower than the tension-related compliance; this finding is in tune with previously reported experimental evidence. The new theory is deemed capable of correctly simulating viscoelastic tension-compression nonlinear behavior.
An approach is explored for modernizing the determination of bulk density of compacted asphalt specimens. It is based on calculating the bulk volume of the specimen in a three-dimensional model reconstructed from its images. The paper... more
An approach is explored for modernizing the determination of bulk density of compacted asphalt specimens. It is based on calculating the bulk volume of the specimen in a three-dimensional model reconstructed from its images. The paper presents the basics of image-based modeling, founded upon the science of photogrammetry and computer vision. Next, a demonstrative application is described, in which a field core is photographed from many viewpoints with a consumer grade camera, and the images are combined into a sparse point cloud. This cloud is subsequently ‘meshed’ with planar polygons into a closed 3D shape and its volume calculated. It was found that the model-core volume was very close to that measured with a traditional liquid-displacement approach. It was also found that while the volume was relatively insensitive to the quantity and quality of the images used for the reconstruction, the computational time varied significantly from minutes to hours. Based on the favorable findings of this limited application, the approach is deemed promising and viable, worthy of more in-depth examination.
A high-end single-axis inertial sensor, capable of detecting minute accelerations, was embedded in an asphalt pavement system. A vehicle of known dimensions and overall weight was driven along a straight line, passing near the sensor's... more
A high-end single-axis inertial sensor, capable of detecting minute accelerations, was embedded in an asphalt pavement system. A vehicle of known dimensions and overall weight was driven along a straight line, passing near the sensor's embedment location at constant speed. Measured accelerations were analyzed as means to infer the pavement layer properties. For this purpose, instead of double integrating the accelerometer data to arrive at deflections, the raw measurements were first smoothed and then matched against computed accelerations. Vehicle speed and weight distribution between front and rear axles were also backcalculated. The paper describes the experimental details, analysis method, and results.
This study targeted the mechanics of asphalt overlayment trackbeds – a ballastless track type that mandates special wide-base sleepers equipped with a geotextile at the bottom. The objective was to develop an analytical model for... more
This study targeted the mechanics of asphalt overlayment trackbeds – a ballastless track type that mandates special wide-base sleepers equipped with a geotextile at the bottom. The objective was to develop an analytical model for quantifying how a geotextile and its compressibility properties influence the contact stress distribution at the sleeper geotextile-asphalt interface. A nonlinear-hardening Winkler spring-bed was utilized to represent a geotextile, a rigid beam was utilized to represent a sleeper, and the pavement system was treated as an elastic half-space. Based on a parametric investigation of the new model it is concluded that the insertion of a geotextile at the sleeper-asphalt interface considerably affects the vertical stress distribution. The presence of a geotextile is shown to produce a more uniform stress distribution and eliminate excessively high contact stresses that would have developed near the sleeper perimeter. It is also shown that geotextile compression adds extra vertical flexibility to the track system with an order of magnitude similar to that of common rail pads. The developed model can handle realistic geotextile compressibility properties as well as any sleeper geometry; its analytical nature provides relative ease of replication for subsequent design and analysis.
Research Interests:
This paper presented an analytic investigation of pavement systems subjected to mill-and-overlay treatments-including grid reinforcement in-between the new asphalt concrete (AC) overlay and the underlying (existing) cracked and aged AC.... more
This paper presented an analytic investigation of pavement systems subjected to mill-and-overlay treatments-including grid reinforcement in-between the new asphalt concrete (AC) overlay and the underlying (existing) cracked and aged AC. The investigation was based on an updated version of the classic layered elastic theory capable of handling a fragmented layer. Such a layer mechanically replicates a multi-cracked AC offering considerable vertical stiffness alongside low bending rigidity. A thin high-modulus layer represented the reinforcing grid, fully bonded to the abutting AC layers. Three mill-and-overlay cases and an additional reference case were investigated for a pavement system under the loading of a dual-tire configuration. The cases differed by the milling depth (thin, medium, and thick), and by the inclusion or exclusion of a reinforcing grid. Key responses in the structure and subgrade, commonly associated with different pavement distress, were calculated and compared across the different cases. The analysis suggests that a reinforcing grid can potentially reduce bottom-up cracking and permanent deformation within the AC overlay for the medium and thick mill-and-overlay cases. For the thin mill-and-overlay case, the analysis suggests that topdown cracking is the expected distress mechanism. In this context, the inclusion of a reinforcing grid seemed to be ineffective. Finally, it is found that adding reinforcement to any of the mill-and-overlay cases produces only a marginal effect on key responses linked to the development of permanent deformation deeper in the structure and subgrade.
Research Interests:
In the context of the Industry 4.0 and civil engineering sector, the Digital Twin (DT) concept has great potential within transportation infrastructure operation and asset management. Its adaption and application could possibly offer: (i)... more
In the context of the Industry 4.0 and civil engineering sector, the Digital Twin (DT) concept has great potential within transportation infrastructure operation and asset management. Its adaption and application could possibly offer: (i) real-time structural monitoring; (ii) support of maintenance-related decisions and activities; and (iii) ability to examine the structural responses under different operational scenarios. This study commences by introducing the DT concept, along with its key components: sensing, modeling, and parameter updating. This is followed by a demonstrative application to an asphalt road – with a focus on its thermal state. The application will involve data from several highway sections equipped with embedded temperature sensors at different depths. The DT will simulate the thermal field evolution in the top 30 cm of the asphalt pavement. At the same time, the DT will provide the time evolution of the thermal diffusivity of the medium.
Research Interests:
Asphalt pavements in cold regions are often exposed to low-temperature cracking distress. The driving mechanism for this type of damage is usually an isolated event of fast surface cooling in combination with low-temperature levels.... more
Asphalt pavements in cold regions are often exposed to low-temperature cracking distress. The driving mechanism for this type of damage is usually an isolated event of fast surface cooling in combination with low-temperature levels. Another common characteristic of pavements in cold regions is the need for salting or mechanical clearing operations (or both) to address ice and snow events. An emerging solution to the latter issue is embedded heating systems-comprising of electric heating elements. These are commonly installed to help melt snow or prevent the accumulation of surface ice. This paper investigated an additional potential benefit of such heating systems-the ability to mitigate the development of low-temperature cracks. Thermomechanical calculations were carried out for an idealized pavement system modeled as a linear viscoelastic half-space. First, simulated winter-weather conditions were imposed to generate a surface crack at some point in time for a pavement without heating. Then after, the simulations were repeated-but with an active heating system. For the case considered, it is found that cracking can be potentially mitigated by the heating system if activated approximately half-an-hour before the time at which crack would occur.
Research Interests:
This study presented the results of numerical analyses for a ballastless asphalt track. The asphalt layer was modelled as a linear viscoelastic (LVE) solid that was resting on an unbound granular layer (UGL) simulated as a non-linear... more
This study presented the results of numerical analyses for a ballastless asphalt track. The asphalt layer was modelled as a linear viscoelastic (LVE) solid that was resting on an unbound granular layer (UGL) simulated as a non-linear (stress-state dependent) elastic medium. The mechanical properties of these layers were calibrated from laboratory element tests. For a given structural arrangement, the model was interrogated under a vertical impulse load to assess the sensitivity of selected responses to temperature and to the initial compaction induced horizontal stresses in the UGL. It was found that horizontal tensile strains at the bottom of the asphalt layer, vertical stresses below the UGL, and vertical surface accelerations were all very sensitive to temperature levels. The vertical surface accelerations were also found to be sensitive to the level of compaction-induced stresses in the UGL. In contrast, the other two responses exhibited a moderate dependency on the lateral stresses. The results from this numerical study provide a better overall understanding of the mechanical behaviour of ballastless asphalt tracks.
Research Interests:
This paper reports the details of a new layered elastic nonlinear cross anisotropic model that can consider the confinement effects of geogrids within pavements. The algorithm, herein called MatLEACANGG, was verified against well-known... more
This paper reports the details of a new layered elastic nonlinear cross anisotropic model that can consider the confinement effects of geogrids within pavements. The algorithm, herein called MatLEACANGG, was verified against well-known programs such as ELLEA2 (Layered Elastic-Cross Anisotropic model) and MichPave (Nonlinear Finite Element Model). Influence of the Geogrid on the vertical microstrain of unbound layers was illustrated via runs on four different structures (with and without Geogrid).
Research Interests:
This paper presented an approach for mechanical pavement condition monitoring based on post-construction installation of near surface LVDTs. The concept calls for making shallow grooves or blind holes at the pavement surface, and then... more
This paper presented an approach for mechanical pavement condition monitoring based on post-construction installation of near surface LVDTs. The concept calls for making shallow grooves or blind holes at the pavement surface, and then fixing horizontal LVDTs to measure any changes in groove length or hole diameter resulting from nearby vehicle passes. A field experiment was designed and executed to demonstrate the approach; it involved the deployment of two LVDTs in an existing asphalt road, and recording the effects of a passing truck. By simulating the experiment with an elastic half-space model, it is shown that the LVDT readings can be matched, leading to the inference of in situ layer moduli.
Research Interests:
The aim of this study is to develop a method for identifying asphalt pavement layer properties based on readings from accelerometers and geophones that are embedded near the ride surface. These sensors are relatively small in size and... more
The aim of this study is to develop a method for identifying asphalt pavement layer properties based on readings from accelerometers and geophones that are embedded near the ride surface. These sensors are relatively small in size and easily embeddable, making them an ideal choice for wide-area applications in the live transportation network. As a first step, a section within the IFSTTAR accelerated pavement testing (APT) facility was instrumented with accelerometers and geophones; also installed was an anchored displacement sensor to serve as a reference/validation device. The APT facility offers the ability to control the loading configuration and intensity, travel speed, and wander (i.e., lateral offset) position relative to the sensor locations. Thus, it becomes possible to isolate the task of property identification through inverse analysis from other real-world complications. The paper commences by describing the experimental setup, and presenting some raw sensor measurements during a single pass of the APT’s wheel carriage. Then, assuming a layered-elastic model, a method is proposed and demonstrated for estimating the pavement moduli. The method is based on best-matching measured velocities and accelerations for the geophones and accelerometers (respectively), with the model predictions- without integrating the signals to convert them into deflections. Very good match is obtained for the sensor readings, and the inferred moduli closely agree with reference values. This outcome means that there is great potential in building a pavement condition monitoring system with near-surface accelerometers and geophones.
Research Interests:
An array of four synchronized single-axis accelerometers was fixed to the surface of an asphalt pavement. Vertical acceleration traces triggered by several nearby passes of a truck with known characteristics were recorded. The work... more
An array of four synchronized single-axis accelerometers was fixed to the surface of an asphalt pavement. Vertical acceleration traces triggered by several nearby passes of a truck with known characteristics were recorded. The work focused on presenting and demonstrating an interpretation method for inferring the mechanical properties of the pavement system based on the recorded accelerations. In general terms, the method was based on careful low-pass filtering the field-measured acceleration traces, and then best-matching them with a corresponding set of calculated acceleration traces. For this purpose, the pavement system was modeled as a two-layered linear elastic half-space, and a model-guided signal filtering approach was devised to ensure that irrelevant signal content is removed prior to the matching. Based on the analysis of six separate truck passes it was noticed that the inferred upper layer modulus exhibited medium variability (coefficient of variation of 45%) while the lower (subgrade) modulus showed little variability (coefficient of variation of 8%). The moduli values displayed fair agreement with those independently estimated from non-destructive and semi-destructive tests. By analyzing many more passes inferred moduli are expected to become more representative. Overall, the method seems workable and scalable, with capacity to handle any number of acceleration sensors as well as other sensor types.
Research Interests:
This study offered a novel method for characterizing the soil support in slab-on-grade constructions such as rigid pavements and raft foundations. The method applies to slabs that are instrumented with fiber-optic cables for distributed... more
This study offered a novel method for characterizing the soil support in slab-on-grade constructions such as rigid pavements and raft foundations. The method applies to slabs that are instrumented with fiber-optic cables for distributed strain sensing; it is based on analyzing the spatial profiles of slab bending strains generated by randomly applied surface loads. The concept was demonstrated for a synthetic case involving an infinite plate resting on a Pasternak support model. The method was shown to deliver non-destructive, non-disruptive, and load-independent quantitative information on the prevailing soil support. Therefore, it is deemed well suited for long-term health monitoring applications of slab-on-grade constructions. Such monitoring can help facility owners evaluate and intercept external events that undermine the integrity of the structure. In the long-term, continued monitoring of soil support can help the engineering community improve analysis approaches and design decisions concerning soil-structure interaction.
Research Interests:
The deformation response of unbound granular materials (UGMs) is composed of two distinct parts: permanent and resilient. Both parts are commonly modelled assuming time-independent behavior. This work focused on the resilient response... more
The deformation response of unbound granular materials (UGMs) is composed of two distinct parts: permanent and resilient. Both parts are commonly modelled assuming time-independent behavior. This work focused on the resilient response part; the objective was to experimentally confirm or invalidate the time-independence assumption. For this purpose, a cylindrical UGM specimen was exposed to a sequence of load-unload-rest in axial compression under two different confinement levels. Resulting strain responses were closely monitored during the rest phases, where no changes in deformation are expected. Nonetheless, it was observed that both axial and radial strains gradually recovered for several minutes subsequent to axial unloading, clearly indicating that the resilient response of the UGM is time-dependent.
Research Interests:
Research Interests:
This work offered a new method for accessing the mechanical properties of pavement layers based on data obtained by a moving measurement platform. The method has the following features: (i) calculations are based on tracking distances to... more
This work offered a new method for accessing the mechanical properties of pavement layers based on data obtained by a moving measurement platform. The method has the following features: (i) calculations are based on tracking distances to a point on the pavement surface, (ii) measurements are not required outside the zone of load influence, and (iii) possibility to access absolute pavement deflections. First, the envisioned platform-design and required readings were presented; next, the interpretation method was outlined and then applied to synthetic (computer-generated) data. Perfect convergence was achieved when the correct pavement model and accurate input data were employed. Also, when artificial errors were introduced for assessing sensitivities, only small deviations were generated. Based on these promising outcomes the method will be further studied and developed to support the construction of an operational measurement platform.
Research Interests:
The aim herein was to equip civil engineers and students with an advanced pavement modeling tool that is both easy to use and highly adaptive. To achieve this, a mathematical solution for a layered viscoelastic half-space subjected to a... more
The aim herein was to equip civil engineers and students with an advanced pavement modeling tool that is both easy to use and highly adaptive. To achieve this, a mathematical solution for a layered viscoelastic half-space subjected to a moving load was developed and subsequently implemented in a spreadsheet environment. The final program can consider up to five fully bonded layers, each isotropic, homogeneous and weightless. The top layer (as well as others if desired) is linear viscoelastic, while the remaining layers are linear elastic. The load is applied vertically to the surface of the system, uniformly spread over a circle, and moving with constant speed along a straight line. The final workbook, named ELLVA1, offers a near real-time solution for the history of stress, strain, and displacement inside the system at any point of interest resulting from a single pass. Despite built-in formulation approximations and limitations of operating under a spreadsheet environment, computation results are shown to be almost exact.
Research Interests:
Two parallel, yet complimentary, paths are being pursued by the scientific community with respect to the future of smart infrastructure. The first focuses on sensor technology and deals with advancing the capabilities and performance of... more
Two parallel, yet complimentary, paths are being pursued by the scientific community with respect to the future of smart infrastructure. The first focuses on sensor technology and deals with advancing the capabilities and performance of the sensory gear. The second focuses on engineering applications and targets the development of interpretation models capable of transforming raw readings into information of engineering worth. This paper presents advancements made within various Israeli universities along these two paths. Firstly, innovations in the field of Brillouin distributed fiber optic sensing are discussed, together with presentation of prospective applications and future research directions. This is followed by an overview of recent advancements in the field of wireless embedded sensors, called Wisdom Stones, for civil engineering applications. It is concluded that expediting a smart infrastructure future requires a multidisciplinary approach in which engineering needs are involved in the development of the sensing techniques.
Research Interests:
This paper tackled the problem of characterizing an object moving along a surface by means of a buried cluster of accelerom-eters. Sought characteristics include: path and speed of movement, number and spatial configuration of contact... more
This paper tackled the problem of characterizing an object moving along a surface by means of a buried cluster of accelerom-eters. Sought characteristics include: path and speed of movement, number and spatial configuration of contact areas, and relative weight distribution across loaded zones. The suggested solution technique was based on solving an inverse problem. For this purpose the passing event was first simulated in a quasi-static mechanical model, and the unknowns were obtained from best matching measured and computed accelerations. The basic solution technique was demonstrated for synthetic acceleration traces generated under ideal conditions. A slightly modified solution technique was proposed for dealing with realistic/field data. Overall, the idea and solution approach are deemed workable , well suited for wireless implementation, and worthy of further development attention.
Research Interests:
This paper explores the potential use of high-resolution fiber optic distributed sensing technology for in situ moduli profiling and in laboratory element testing. In recent times, strain measurement using fiber optics has been employed... more
This paper explores the potential use of high-resolution fiber optic distributed sensing technology for in situ moduli profiling and in laboratory element testing. In recent times, strain measurement using fiber optics has been employed in innovative civil engineering applications such as in the health monitoring of ageing infrastructures. Through recent developments, in particular Rayleigh backscatter optical frequency domain reflectometry technique, the fiber optic sensing technology is nowadays capable of providing continuous distributed strain measurement with a higher spatial resolution of the order of millimeters. As a result, the technology can potentially serve as a viable alternative to conventional strain gauges (i.e. high-spatial resolution yet localized measurement devices) or seismic geophysical measurement (i.e. distributed yet low-spatial resolution). This paper provides two examples of its applicability to both in situ and laboratory mechanical characterization.
Research Interests:
High-resolution Brillouin optical correlation domain analysis of fibers embedded within beams of composite materials is performed with 4 cm resolution and 0.5 MHz sensitivity. Two new contributions are presented. First, analysis was... more
High-resolution Brillouin optical correlation domain analysis of fibers embedded within beams of composite materials is performed with 4 cm resolution and 0.5 MHz sensitivity. Two new contributions are presented. First, analysis was carried out continuously over 30 hours following the production of a beam, observing heating during exothermal curing
and buildup of residual strains. Second, the bending stiffness and Young's modulus of the composite beam were extracted based on distributed strain measurements, taken during a static three-point bending experiment. The calculated parameters were used to forecast the beam deflections. The latter were favorably compared against external displacement measurements.
and buildup of residual strains. Second, the bending stiffness and Young's modulus of the composite beam were extracted based on distributed strain measurements, taken during a static three-point bending experiment. The calculated parameters were used to forecast the beam deflections. The latter were favorably compared against external displacement measurements.
Research Interests:
One of the problems affecting mature fields in the North Sea is seabed subsidence due to reservoir depletion. Seabed subsidence can directly affect integrity of production facilities. Severe subsidence, as in the case of the Ekofisk... more
One of the problems affecting mature fields in the North Sea is seabed subsidence due to reservoir depletion. Seabed subsidence can directly affect integrity of production facilities. Severe subsidence, as in the case of the Ekofisk field, can lead to platform sinking below the sea level and, subsequently, to very high repair costs or possibly to a complete platform replacement. Subsidence is an issue also in the Tyra field, and it may become a problem in other fields as depletion is ongoing. Fluid injection is a widely used method to boost production and/or maintain reservoir pressure in order to mitigate compaction and subsidence. Both reservoir depletion and fluid injection operations induce seabed deformations. The deformation pattern potentially holds useful information about production efficiency and reservoir management, which could be captured by careful and continuous monitoring of seabed strains. Current technologies for monitoring offshore seabed deformations only provide point or line readings. The idea that this sprint project explores is achieving nearly full-field and continuous monitoring of seabed surface deformations by means of distributed fiber optic sensors. The objective of the study was to theoretically assess whether current fiber optic sensing technology is sensitive enough to detect production-induced seabed strains originating at a 2000 m deep reservoir.
Research Interests:
Asphalt-aggregate mixes are being used throughout the world as a prime construction material for pavements. An asphalt mix is a multiphase heterogeneous material; it is a composite blend of air-voids, asphalt-cement (bitumen) and... more
Asphalt-aggregate mixes are being used throughout the world as a prime construction material for pavements. An asphalt mix is a multiphase heterogeneous material; it is a composite blend of air-voids, asphalt-cement (bitumen) and aggregates of a range of sizes. These materials exhibit extremely complex mechanical behavior that is very difficult to capture and model. Mainly for this reason available pavement-performance models are empirical, as no rigorous constitutive models were yet formulated for asphalt mixes.
The motivation underlying this research work was to improve material modeling and characterization techniques for asphalt-aggregate mixes. An up-to-date review of literature revealed that current characterization efforts are limited principally because they deal with material behavior in uniaxial tests and provide essentially one-dimensional models.
This dissertation presents the development of a triaxial viscoelastic-viscoplastic constitutive model for asphalt mixes including the effects of damage and healing. The model is confined to the description of pre-peak load response under isothermal conditions. It is based on additive separation of the total strain into viscoelastic and viscoplastic components and provides individual constitutive treatment to each part.
The viscoelastic formulation is nonlinear, cross-anisotropic, and characterized by one unique (scalar) time-function. Three nonlinear isotopic effects are modeled: i) damage, i.e. loss of stiffness under load; ii) stiffening, i.e. increase of stiffness under compression conditions, and iii) healing, i.e., a decrease in the level of damage during rest periods. The viscoplastic equations resemble the kinematic-hardening formulations used to describe creep of metals. Internal stress-like variables are used to produce hardening (or softening) in each direction. Neither damage nor healing is included in the viscoplastic model. It should be noted that coupling is introduced between the individual formulations, making the viscoelastic response dependent also on the viscoplastic component.
In order to support the development of the constitutive formulation, new experimental procedures were designed and executed using the triaxial apparatus. Creep and recovery test results are presented and analyzed, providing means (also) to calibrate and validate the model for biaxial stress-conditions and one test temperature. Good reproducibility and forecast-ability were obtained in the analyses of versatile test-data for both small and large strain load-cycles; indicating that the model is suitable for simulating the 3D load-response of asphalt-aggregate mixes.
The constitutive development in this study constitutes the first attempt to describe the triaxial (viscoelastic-viscoplastic) load-response of asphalt materials including damage and healing. Several aspects of this development were found limited - specifically the ability to rigorously describe the viscoplastic behavior after large rest periods. Further research is needed to try and resolve this limitation and remove some of the other formulation restrictions.
The motivation underlying this research work was to improve material modeling and characterization techniques for asphalt-aggregate mixes. An up-to-date review of literature revealed that current characterization efforts are limited principally because they deal with material behavior in uniaxial tests and provide essentially one-dimensional models.
This dissertation presents the development of a triaxial viscoelastic-viscoplastic constitutive model for asphalt mixes including the effects of damage and healing. The model is confined to the description of pre-peak load response under isothermal conditions. It is based on additive separation of the total strain into viscoelastic and viscoplastic components and provides individual constitutive treatment to each part.
The viscoelastic formulation is nonlinear, cross-anisotropic, and characterized by one unique (scalar) time-function. Three nonlinear isotopic effects are modeled: i) damage, i.e. loss of stiffness under load; ii) stiffening, i.e. increase of stiffness under compression conditions, and iii) healing, i.e., a decrease in the level of damage during rest periods. The viscoplastic equations resemble the kinematic-hardening formulations used to describe creep of metals. Internal stress-like variables are used to produce hardening (or softening) in each direction. Neither damage nor healing is included in the viscoplastic model. It should be noted that coupling is introduced between the individual formulations, making the viscoelastic response dependent also on the viscoplastic component.
In order to support the development of the constitutive formulation, new experimental procedures were designed and executed using the triaxial apparatus. Creep and recovery test results are presented and analyzed, providing means (also) to calibrate and validate the model for biaxial stress-conditions and one test temperature. Good reproducibility and forecast-ability were obtained in the analyses of versatile test-data for both small and large strain load-cycles; indicating that the model is suitable for simulating the 3D load-response of asphalt-aggregate mixes.
The constitutive development in this study constitutes the first attempt to describe the triaxial (viscoelastic-viscoplastic) load-response of asphalt materials including damage and healing. Several aspects of this development were found limited - specifically the ability to rigorously describe the viscoplastic behavior after large rest periods. Further research is needed to try and resolve this limitation and remove some of the other formulation restrictions.
Research Interests:
This is a Small-Element Pavement Analysis (SEPA) worksheet, version 0.2 (November 2023). It solves a semi-analytical formulation of a layered elastic half-space with a P-Type Fragmented Layer (FL) on top. More details on the formulation... more
This is a Small-Element Pavement Analysis (SEPA) worksheet, version 0.2 (November 2023). It solves a semi-analytical formulation of a layered elastic half-space with a P-Type Fragmented Layer (FL) on top.
More details on the formulation can be found in Levenberg, E. and Skar, A. (2022), “Analytic Pavement Modeling with a Fragmented Layer,” International Journal of Pavement Engineering, 23(4), 1108–1120.
More details on the formulation can be found in Levenberg, E. and Skar, A. (2022), “Analytic Pavement Modeling with a Fragmented Layer,” International Journal of Pavement Engineering, 23(4), 1108–1120.
Research Interests:
ELLEA1(FWD) – Backcalculation in Excel (July 23, 2023). This worksheet was developed for teaching students and engineers the basics of elastostatic backcalculation of Falling Weight Deflectometer (FWD) measurements.
Research Interests:
ELLVA_VD: Isotropic Layered Viscoelasticity in Excel: Analysis tool for interpretation of deflections measured with a moving load. This is basically a fast version of ELLVA1 tailored for inverse analysis. Accordingly, only vertical... more
ELLVA_VD: Isotropic Layered Viscoelasticity in Excel: Analysis tool for interpretation of deflections measured with a moving load. This is basically a fast version of ELLVA1 tailored for inverse analysis. Accordingly, only vertical surface displacements are computed. Three empty Worksheets were added to enable side-calculations.
Research Interests:
The worksheet ELiCon (version 0.1) performs real-time viscoelastic interconversion in the time and frequency domains. ELiCon accepts as input a four-parameter analytical expression for the uniaxial creep compliance. The time-domain output... more
The worksheet ELiCon (version 0.1) performs real-time viscoelastic interconversion in the time and frequency domains. ELiCon accepts as input a four-parameter analytical expression for the uniaxial creep compliance. The time-domain output consists of a list of creep compliance values for certain times, and a corresponding list of relaxation modulus values. The frequency-domain output consists of, for certain frequencies, the norm of the complex modulus and the phase angle.
Research Interests:
ELLVA1 (Ver 0.83) computes stresses, strains and displacements in a layered viscoelastic half-space due to a uniformly loaded circular area moving with constant speed along a straight line. Five fully bonded weightless, homogeneous, and... more
ELLVA1 (Ver 0.83) computes stresses, strains and displacements in a layered viscoelastic half-space due to a uniformly loaded circular area moving with constant speed along a straight line. Five fully bonded weightless, homogeneous, and isotropic layers are considered. Developed by Dr. Eyal Levenberg, Technion-IIT, January 2016.
Research Interests:
ELLEA1 (version 1.00) computes stresses, strains, and displacements in a layered elastic half-space due to two uniformly loaded (dissimilar) circular areas. Five fully bonded weightless, homogeneous, and isotropic layers are considered.... more
ELLEA1 (version 1.00) computes stresses, strains, and displacements in a layered elastic half-space due to two uniformly loaded (dissimilar) circular areas. Five fully bonded weightless, homogeneous, and isotropic layers are considered. Developed under JTRP Project 2813 by Dr. Eyal Levenberg, North Central Superpave Center, Purdue University, November 2008 (November 2023 update). For questions, requests, and comments contact: eyal.levenberg@yahoo.com.
ELLEA2 performs real time computation of stresses, strains and displacements in a layered elastic half-space due to two uniformly loaded circular areas applied at the surface (Excel 2007 spreadsheet). Five fully bonded layers are... more
ELLEA2 performs real time computation of stresses, strains and displacements in a layered elastic half-space due to two uniformly loaded circular areas applied at the surface (Excel 2007 spreadsheet). Five fully bonded layers are considered, each weightless, homogenous, and transversely-isotropic.
Link: https://www.amazon.com/dp/8797231703 This book introduces purely mechanistic models that are of particular relevance to the pavement engineering profession. It commences with a short recap of basic mechanics concepts, and then... more
Link: https://www.amazon.com/dp/8797231703
This book introduces purely mechanistic models that are of particular relevance to the pavement engineering profession. It commences with a short recap of basic mechanics concepts, and then delves into topics such as viscoelasticity, elastic half-space solutions, and mechanics of supported plates. Given that all pavement design and analysis approaches are founded on some mechanistic logic, the text essentially offers a universal and long-lasting reference to practitioners and engineering students.
This book introduces purely mechanistic models that are of particular relevance to the pavement engineering profession. It commences with a short recap of basic mechanics concepts, and then delves into topics such as viscoelasticity, elastic half-space solutions, and mechanics of supported plates. Given that all pavement design and analysis approaches are founded on some mechanistic logic, the text essentially offers a universal and long-lasting reference to practitioners and engineering students.
Research Interests:
Links to three video clips of myself explaining the basic concepts of linear viscoelasticity in connection to asphalt concrete:
Part 1: https://youtu.be/2tzEEfKkF5g
Part 2: https://youtu.be/7uCnDv1ItyE
Part 3: https://youtu.be/kegPzLuWqzc
Part 1: https://youtu.be/2tzEEfKkF5g
Part 2: https://youtu.be/7uCnDv1ItyE
Part 3: https://youtu.be/kegPzLuWqzc
Research Interests:
My 2021 updated notes for DTU 11451: "Pavement Mechanics." This is a Master level course (5 ECTS) covering advanced topics related to the mechanics of both asphalt and concrete pavements. The notes only cover the first part of the course... more
My 2021 updated notes for DTU 11451: "Pavement Mechanics." This is a Master level course (5 ECTS) covering advanced topics related to the mechanics of both asphalt and concrete pavements. The notes only cover the first part of the course dealing with asphalt pavements. Some of the concrete-related notes (and more) are included in my book: https://www.polyteknisk.dk/home/Detaljer/9788797231708
My presentation slides for DTU 11450: "Basic Course in Road Pavements." This is a bachelor level course (5 ECTS) covering introductory topics related to pavement design, focusing on asphalt pavements. Its main objective is exposition of... more
My presentation slides for DTU 11450: "Basic Course in Road Pavements." This is a bachelor level course (5 ECTS) covering introductory topics related to pavement design, focusing on asphalt pavements. Its main objective is exposition of the students to the scope, complexity, and opportunities in this field.
My presentation slides for DTU 11451: "Pavement Mechanics."
This is a Master level course (5 ECTS) dealing with advanced asphalt pavement topics (i.e., flexible pavements) and jointed plain concrete pavements (i.e., rigid pavements).
This is a Master level course (5 ECTS) dealing with advanced asphalt pavement topics (i.e., flexible pavements) and jointed plain concrete pavements (i.e., rigid pavements).
https://www.youtube.com/watch?v=LL7urot0ugw
This short clip presents the journal article: "Analytic Pavement Modelling with a Fragmented Layer."
This short clip presents the journal article: "Analytic Pavement Modelling with a Fragmented Layer."
Research Interests:
A method for uncovering the nonlinear viscoelastic behavior of asphalt concrete is presented and applied to some test data. The material appears highly non-linear, especially under very small strains. Also, healing seems to be a dominant... more
A method for uncovering the nonlinear viscoelastic behavior of asphalt concrete is presented and applied to some test data. The material appears highly non-linear, especially under very small strains. Also, healing seems to be a dominant feature. Lastly, the nonlinear behavior is different between tension and compression.
Research Interests:
Recorded presentation for MAIREPAV9 (2020)
Research Interests:
Research Interests:
Exposition of the ELLVA1 code: Isotropic Layered Viscoelasticity in Excel. This is an advanced pavement analysis tool for students and engineers. Download at:... more
Exposition of the ELLVA1 code: Isotropic Layered Viscoelasticity in Excel. This is an advanced pavement analysis tool for students and engineers.
Download at:
https://orbit.dtu.dk/en/activities/ellva1-isotropic-layered-viscoelasticity-in-excel-moving-load-adv
Download at:
https://orbit.dtu.dk/en/activities/ellva1-isotropic-layered-viscoelasticity-in-excel-moving-load-adv