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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields (Vol. 3), 2022
This study targeted the mechanics of asphalt overlayment trackbeds – a ballastless track type tha... 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.
Proceedings of the Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields (Volume 1), 2022
This paper presented an analytic investigation of pavement systems subjected to mill-and-overlay ... 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.
Proceedings of the 2021 International Symposium on Frontiers of Road and Airport Engineering (iFRAE 2021), 2021
In the context of the Industry 4.0 and civil engineering sector, the Digital Twin (DT) concept ha... 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.
Proceedings of the 2020 RILEM International Symposium on Bituminous Materials (ISBN), 2021
Asphalt pavements in cold regions are often exposed to low-temperature cracking distress. The dri... 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.
Proceedings of the 16th Conference of the International Association for Computer Methods and Advances in Geomechanics (IACMAG), 2021
This study presented the results of numerical analyses for a ballastless asphalt track. The aspha... 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.
Advances in Materials and Pavement Performance Prediction II, 2020
This paper reports the details of a new layered elastic nonlinear cross anisotropic model that ca... 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).
Advances in Materials and Pavement Performance Prediction II, 2020
This paper presented an approach for mechanical pavement condition monitoring based on post-const... 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.
Proceedings of 6th APT Conference: Accelerated Pavement Testing to Transport Infrastructure Innovation, 2020
The aim of this study is to develop a method for identifying asphalt pavement layer properties ba... 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.
Proceedings of the 9th International Conference on Maintenance and Rehabilitation of Pavements (Mairepav9), 2020
An array of four synchronized single-axis accelerometers was fixed to the surface of an asphalt p... 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.
This study offered a novel method for characterizing the soil support in slab-on-grade constructi... 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.
Proceedings of the 17th European Conference on Soil Mechanics and Geotechnical Engineering (XVII ECSMGE), 2019
The deformation response of unbound granular materials (UGMs) is composed of two distinct parts: ... 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.
Proceedings of the ARTEK International Conference (AIC 2018) on Transportation Infrastructure Engineering in Cold Climates, May 1-3, Sisimiut, Greenland, pp. 76–77, 2018
This work offered a new method for accessing the mechanical properties of pavement layers based o... 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.
Proc. of the Eighth Intl. Conf. on Maintenance and Rehabilitation of Pavements, Jul 2016
The aim herein was to equip civil engineers and students with an advanced pavement modeling tool ... 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.
Two parallel, yet complimentary, paths are being pursued by the scientific community with respect... 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.
This paper tackled the problem of characterizing an object moving along a surface by means of a b... 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.
This paper explores the potential use of high-resolution fiber optic distributed sensing technolo... 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.
Proceedings of the 24th International Conference on Optical Fibre Sensors, Aug 20, 2015
High-resolution Brillouin optical correlation domain analysis of fibers embedded within beams of ... 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.
One of the problems affecting mature fields in the North Sea is seabed subsidence due to reservoi... 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.
Asphalt-aggregate mixes are being used throughout the world as a prime construction material for ... 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.
This is a Small-Element Pavement Analysis (SEPA) worksheet, version 0.2 (November 2023). It solve... 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.
ELLEA1(FWD) – Backcalculation in Excel (July 23, 2023). This worksheet was developed for teaching... more 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.
ELLVA_VD: Isotropic Layered Viscoelasticity in Excel: Analysis tool for interpretation of deflect... 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.
The worksheet ELiCon (version 0.1) performs real-time viscoelastic interconversion in the time an... 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.
ELLVA1 (Ver 0.83) computes stresses, strains and displacements in a layered viscoelastic half-spa... 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.
ELLEA1 (version 1.00) computes stresses, strains, and displacements in a layered elastic half-spa... 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... 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.
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.
My 2021 updated notes for DTU 11451: "Pavement Mechanics." This is a Master level course (5 ECTS)... 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 ... 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 ECT... more 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).
A method for uncovering the nonlinear viscoelastic behavior of asphalt concrete is presented and ... 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.
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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.
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.
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.
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.
Part 1: https://youtu.be/2tzEEfKkF5g
Part 2: https://youtu.be/7uCnDv1ItyE
Part 3: https://youtu.be/kegPzLuWqzc
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 short clip presents the journal article: "Analytic Pavement Modelling with a Fragmented Layer."
Download at:
https://orbit.dtu.dk/en/activities/ellva1-isotropic-layered-viscoelasticity-in-excel-moving-load-adv