Journal Publications by Eyal Levenberg
A Digital Twin Concept for Civil Infrastructure
Journal of Infrastructure Systems, 2024
In broad terms, a digital twin is a continuously updated virtual representation of some targeted ... more In broad terms, a digital twin is a continuously updated virtual representation of some targeted physical reality. The objective of this technical note is to contribute to the current/ongoing efforts of delineating the digital twin concept within the civil engineering domain. An adult digital twin concept is described and exemplified for this purpose–applicable to mature civil infrastructure and with the primary aim of monitoring changes in state over time. The analysis advocates for clearly separating the real and virtual spaces by focusing on objective physical entities as state descriptors, i.e., entities that are not inherently coupled to any specific modeling framework. Also, the analysis emphasizes that model updating consists of two distinct activities, namely parameter updating (Type I) and formulation updating (Type II)—with the latter type requiring research attention.
Verification and Validation of Pavement Models
Journal of Transportation Engineering, Part B: Pavements, 2024
Model development activities are increasing in pavement research and engineering applications. At... more Model development activities are increasing in pavement research and engineering applications. At the same time, there is ambiguity and a lack of consistency with regard to checking and quantifying credibility and suitability for the intended application. Specifically, usage of the terms Verification and Validation (V&V) is seen to vary across contributions. In this context, this paper was motivated by the desire to provide a best-practice reference that underlines the significance of the V&V terms, clarifies their definition, and promotes a more unified usage. Accordingly, the objective was to offer examples that introduce the V&V jargon, demonstrate basic V&V concepts and processes, and highlight certain fine points. A total of five distinct models were introduced and discussed: (1) load-related responses in asphalt pavements, (2) load-related responses in concrete pavements, (3) crack initiation and propagation in asphalt concrete, (4) linear viscoelasticity of asphalt concrete, and (5) water flow through asphalt concrete pores. A general conclusion from this work is that successful V&V efforts are closely linked to a clear definition of the intended usage, i.e., the specific reality of interest being targeted by the model. It is also concluded that documenting V&V efforts is integral to any computational model development. Doing so communicates to potential users the region of confidence for the model alongside the expected differences with the reality of interest.
Mechanistic Investigation of Grid-reinforced Asphalt Pavements with Measured Interface Properties
Road Materials and Pavement Design, 2024
The bond properties at layer interfaces are a required input in mechanistic asphalt pavement mode... more The bond properties at layer interfaces are a required input in mechanistic asphalt pavement models. For design and analysis procedures, involving the calculation of key responses that are commonly linked to performance, perfect bond conditions are regularly assumed between layers. One emerging approach for prolonging the service life of asphalt pavements, either new or rehabilitated, is installing asphalt grid reinforcement (AGR) products between paving lifts. In these cases, the perfect bond assumption may not hold – undermining the reinforcement potential. Accordingly, the objective of this study was to investigate the effects of layer interface properties on key responses in pavements with AGR. The investigation was carried out by combining results from a full-scale construction, laboratory tests on asphalt concrete (AC) cores, and synthetic simulations. The latter were performed with a recently developed semi-analytic mechanistic code that can accept AGR products. This code can handle time- and temperature-dependent layer and interface properties, as well as moving loads. From the laboratory tests, it was found that the bond between AC lifts, with and without an AGR, is time- and temperature-dependent – best characterized by a relaxation interface stiffness function. This relaxation function was measured to be consistently larger without an AGR than with an AGR. Nonetheless, pavement simulations showed that including an AGR has no pronounced effect on strain magnitudes under high-speed/low-temperature conditions, can lessen horizontal strain magnitudes at the reinforced interface and at the AC bottom (mainly under slow-speed/high-temperature conditions, and depending on the installation depth of the AGR), and has no pronounced effect on deflections regardless of the loading speed and temperature level. It is concluded that even if laboratory measurements display a reduced interface stiffness when including an AGR, the reduction may not have any practical implication on key pavement responses, and the reinforcement potential is not necessarily undermined. The modeling and experimental approaches outlined and utilized in this study offer a rational tool for analyzing this matter/question on a case-by-case basis.
Mechanistic Code for Asphalt Pavements Loaded by Farming Vehicles
Transportation Research Record: Journal of the Transportation Research Board, 2023
Full-scale validation of a mechanistic model for asphalt grid reinforcement
International Journal of Pavement Engineering, 24(1), 2023
Road Profile Inversion from In-Vehicle Accelerometers
Journal of Transportation Engineering, Part B: Pavements, 2023
Estimating the Tire–Pavement Grip Potential From Vehicle Vibrations
Transportation Research Record, 2023
This study was motivated by the desire to provide highway managers/operators with more frequent a... 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.
Modeling the use of an Electrical Heating System to Actively Protect Asphalt Pavements against Low-Temperature Cracking
Cold Regions Science and Technology, 2022
This paper addressed the case of an electrically heated asphalt pavement; it explored an unconven... more This paper addressed the case of an electrically heated asphalt pavement; it explored an unconventional application of such a system – not for combating snow and ice – but for mitigating low-temperature cracking. The investigation was done in silico, considering a stratified medium to represent the asphalt pavement system, a thin heat-generating layer to represent the heating system, and measured weather conditions from Greenland to emulate a cold region that can potentially produce thermal cracking. A thermomechanical model was outlined, consisting of a one-dimensional thermal formulation that accounts (also) for latent heat effects, and a three-dimensional mechanical formulation based on linear viscoelasticity that assumes thermo-rheological simplicity. A cold-weather event, leading to a thermal crack, was identified by the thermomechanical model. Additionally, a parametric investigation was carried out to quantify the effects of the heating system’s embedment depth and heating production on the activation timing needed to prevent cracking. It is found that mitigating low-temperature cracking with an embedded electric heating system is attainable and workable. Doing so is most effective when the heating system resides close to the ride surface. A procedure for automatic heating operation was proposed for practical implementation.
Protecting Asphalt Pavements against Frost Action with an Electrical Heating System: Numerical Investigation
Journal of Cold Regions Engineering, 2022
This paper is concerned with electrically heated asphalt pavements; it numerically explores the p... 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.
Mechanistic Modelling of Grid-Reinforced Milled-and-Overlaid Asphalt Pavements
International Journal of Pavement Engineering, 2022
This study was motivated by the need for a mechanistic-empirical (ME) design method applicable to... 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.
Live Road Condition Assessment with Internal Vehicle Sensors
Transportation Research Record, 2021
Modern cars are equipped with many sensors that measure information about the vehicle and its sur... 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.
Construction of an Electrically Heated Asphalt Road based on Ribbon Technology
Transportation Research Record, 2021
Although asphalt pavements are the most common pavement type worldwide, there is no accepted heat... more Although asphalt pavements are the most common pavement type worldwide, there is no accepted heating solution for this infrastructure class for melting snow and preventing ice formation at the ride-surface. This study was concerned with utilizing electric ribbon technology as a suitable heating solution. A method was proposed to introduce ribbon heaters into the typical paving process in a practical manner, causing minimal disruption to the normal paving operations, that is potentially expandable to large areas. The advocated idea was to deploy ribbons after an asphalt concrete (AC) lift has been paved and compacted, and before paving and compacting the next AC lift(s). In this context, a special grooving machine was envisioned to make shallow channels in the AC for cradling each ribbon. Thus, the system survivability is guaranteed, with all ribbons protected against the maneuvering of trucks, paving equipment, and heavy rollers. Subsequently, the method was demonstrated through the full-scale construction of a heated road that included installing ribbons in-between AC lifts. For this purpose, the protective ribbon channels were grooved with a customized milling machine. The entire construction process was described in detail, and some initial findings from activating the system were also included. An overall system survivability of 97% was achieved, and the installation concept appears practical and up-scalable.
Numerical Modeling of a Ballastless Track Mockup based on Asphalt
Construction and Building Materials, 2021
A 3D mechanical model of a ballastless asphalt track mockup was developed within the general-purp... 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.
Analytic Pavement Modeling with a Fragmented Layer
International Journal of Pavement Engineering, 2020
Layered elastic theory is a familiar and commonly accepted framework for modelling and analysis o... 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.
Experimental Investigation of a Ballastless Asphalt Track Mockup under Vertical Loads
Construction and Building Materials, 2020
This study presents experimental results from a laboratory investigation into the mechanical beha... more This study presents experimental results from a laboratory investigation into the mechanical behaviour of a ballastless asphalt track under vertical loads and isothermal conditions. A full-scale test section was constructed inside a steel box, consisting of three wide-base sleepers resting on an asphalt layer that was underlain by an unbound granular layer (UGL) supported on a rubber mat (representing subbase and subgrade). Sensors were installed to measure diverse responses, consisting of vertical stresses at the bottom of the UGL, horizontal strains at the bottom of the asphalt layer, relative vertical displacements between various track components, and vertical surface accelerations. Sleepers were loaded directly on top of the rail pads by using servo-hydraulic actuators. Cyclic loads were applied to investigate the effects of different excitation amplitudes and frequencies. It was found that all measured responses displayed a strong frequency dependence. Vertical stresses below the UGL varied linearly with the load amplitude, while other responses showed a non-linear relationship. Train passages with a maximum speed of 200 km/h and axle loads up to 200 kN were simulated by sequentially loading the three sleepers. From this load type, it was found that ballastless asphalt track exhibited time-dependent behaviour such as delayed recovery of strains in-between axle passes. Furthermore, the majority of the vertical actuator displacement was absorbed by rail pad compression. Lastly, measured stresses and strains were of very low magnitudes, suggesting marginal long term mechanical damage under service loads for such a ballastless asphalt track structure.
A Priori Determination of Track Modulus Based on Elastic Solutions
KSCE Journal of Civil Engineering, 2020
The standard approach for modeling railway tracks idealizes the rails as two infinite beams, each... more The standard approach for modeling railway tracks idealizes the rails as two infinite beams, each supported over a separate continuous spring foundation. The foundation is characterized by a track modulus that embodies all components and materials underlying each rail as well as any cross-rail interaction. Track modulus is considered a basic parameter governing the field performance of tracks. Therefore, a priori determination of track modulus is needed in design of traditional railways, as well as in evaluating the performance-potential of non-traditional track solutions. In this study, a new method was suggested for a priori track modulus determination based on elastic solutions. Specifically sought were closed-form analytical formulations that could be representative and tractable. In this connection, a 3-D track model was developed, wherein: rail-pads were considered as linear springs, sleepers as finite beams, and all underlying soil-like materials as a homogenous half-space. Ultimately, track modulus was determined by linking calculations in the 3-D model and the standard model. This was done by requiring equal maximal displacement as well as identical load distribution along the rail under the weight of a single railcar axle. The method was illustrated considering a wide set of values for the different model parameters. The calculated results are comparable in magnitudes and exhibit similar sensitivities to the input parameters as reported in field studies or as derived from elaborate numerical schemes.
Analysis of a Moving Measurement Platform based on Line Profile Sensors for Project-Level Pavement Evaluation
Road Materials and Pavement Design, 2020
In recent years, there has been renewed interest in developing Moving Measurement Platforms (MMPs... 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.
First Break, 2020
One of the problems affecting mature hydrocarbon fields, e.g., Ekofisk, Tyra, and Dan in the Nort... 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.
On The Thermal Sensitivity of Unbound Granular Pavement Layers
International Journal of Pavement Research and Technology, Vol. 13, pp. 32–39., 2020
The reversible mechanical behavior of unbound granular layers (UGLs) is commonly characterized by... 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.
Sensors 2019, 19, 3518, 2019
The evaluation of soil reaction in geotechnical foundation systems such as concrete pavements, ma... 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.
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Journal Publications by Eyal Levenberg