Multilayer Elastic Theory Research Articles

Optimizing Geotechnical Data Input Based on Light Weight Deflectometer for Road Design and Performance Analysis

This study explores alternative methods for assessing critical parameters in pavement design, specifically Young’s modulus and Poisson’s ratio. While repeated load triaxial testing is traditionally used, its high cost and time requirements drive the search for more efficient methods. Falling weight deflectometer tests are also resource-intensive, leading to the investigation of light weight deflectometer tests. Utilizing EraPave software for analysis, which employs a multi-layer elastic theory back-calculation tool, the research examines material properties through laboratory tests on unbound granular material, sandy soil, silty sand soil, and sandy silty clay soil, providing data for field tests. Field LWD tests, conducted under various moisture contents and dynamic loads, provided data processed through EraPave to predict layer moduli. Results demonstrate LWD’s effectiveness in predicting layer moduli for different construction materials. Despite variations in root mean square error values, LWD data consistently align well with EraPave predictions, underscoring its reliability for pavement evaluation. Case studies illustrate LWD and EraPave’s adaptability to different moisture contents and stresses. This study advocates for LWD tests’ efficiency and highlights the importance of analytical tools like EraPave for accurate pavement assessments, contributing to optimized pavement evaluation processes and informed road construction and maintenance decisions.

Thickness ranges calculation method of double asphalt overlay on concrete pavement

Asphalt overlay is widely used in maintaining and rehabilitating highway system performance. However, explicit calculation methods for the asphalt overlay thickness range is lacking. Taking stone mastic asphalt (SMA) and asphalt concrete (AC) asphalt overlay on cement concrete pavement as examples, the paper proposed a design method for the asphalt overlay thickness range based on the shear performance of the interlayer. Firstly, the shear stress distribution regularities on the asphalt overlay and Portland cement concrete interlayer was calculated with a multilayer elastic theory. Meanwhile, the shear strength was obtained from a series of direct shear tests. The shear characters of the asphalt overlay met with the Mohr–Coulomb criterion, and the shear strength parameters cohesive force c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$c$$\\end{document} and interface friction angle φ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi$$\\end{document} on the interlayer were acquired. Finally, a method for determining the thickness range of double layer asphalt overlay under different traffic conditions was given. The epoxy resin adhesive was recommended for the highway with severe local premature shear failure compared with the modified emulsion asphalt. Therefore, through the above research, the amount of asphalt used is controlled in a reasonable range, thus improving the pavement structure durability and reducing energy consumption.

DEEP NEURAL NETWORKS FOR SENSITIVITY ASSESSMENT OF DESIGN VARIABLES ON THE STRUCTURAL DESIGN PARAMETERS OF FLEXIBLE PAVEMENTS FOR LOW-TRAFFIC VOLUME ROADS

This study aims to implement deep neural networks (DNNs) to assess the sensitivity level of design parameters in flexible pavements for roads with low traffic volume. One hundred eight structures were modeled using the Pitra Pave® software (i.e., multilayer elastic theory (MET) model for pavement structural analysis) to generate a database to develop the DNN models. The DNN models, through connection weights, allowed the comparison with MET to evaluate the sensitivity of the selected design variables (resilient modulus and layer thickness) on the structural design parameters. The results suggest the significant impact of layer thicknesses. In addition, the predictions of structural design parameters from these initial DNN models showed variations ranging from 0,03% to 10,87% compared to MET. Expanding the database and developing a multi-predictive network is recommended for future research.

A step toward improving management practices for airfield pavement infrastructures: a mechanistic-based analysis approach

Conventional performance indicators commonly used to evaluate airfield pavement infrastructures focus on surface condition assessment. However, the structural soundness of pavements remains a key element in determining the best intervention measures. Methods used worldwide to design and evaluate flexible airfield pavements are often based on the Multi-Layered Elastic Theory (MLET). The Federal Aviation Administration (FAA) also applies MLET to analyse data collected primarily with on-site Non-Destructive Testing (NDT). However, material behaviour is not always aligned with MLET assumptions. In this study, pavement analysis results are investigated from a mechanistic view considering, in particular, the viscoelastic properties of Asphalt Concrete (AC). The analysis is performed using NDT and coring data collected in-situ from a runway considering variable aircraft loading and moving speeds. Based on the response status at both critical locations of a flexible pavement plus its surface, it is observed that MLET appears to be less conservative at normal operating speeds, where higher pavement damage is expected. In addition, an integration potential of viscoelastic strains and NDT data is shown, which can accelerate the pavement evaluation process. It is expected that the presented approach can provide a framework for improving airfield pavement management practices.

Monitoring and Simulating the Responses of Four Flexible Pavement Test Sections under Heavy Vehicle Loading

Abstract For mechanistic-empirical design of pavements, it is essential to accurately predict the responses of the structure that are caused by the design traffic loading. The aim of this study was to compare the simulated responses of pavements with real measurements under heavy vehicle loading. With this objective, four instrumented test sections were built in northern Sweden—about 100 km north of the Arctic Circle. These test sections differed in material quality of the various layers. Each test section was instrumented with pressure cells and strain sensors that measured the pavement response to external loading. Climatic variables were monitored through a weather station as well as temperature and moisture sensors installed in the road structures. Response measurements were carried out using 25-m-long 10-axle vehicles with gross weight of 90 tons. For the simulations of the responses of these test structures under the same vehicular loading, a multilayer elastic theory–based program called ERAPave was used. The required material properties for the simulations were based on laboratory testing of core-drilled samples from the sites. For the simulations, three combinations of material characterizations were considered: (a) linear elastic (LE) all layers, (b) nonlinear (NL) unbound layers, and (c) viscoelastic (VE) asphalt layers. Acceptable agreement between the simulations and measured responses were observed. Generally, the responses calculated based on LE and NL analyses were indistinguishable, whereas the VE analyses showed somewhat lower amplitude peaks.

Sensitivity analysis of pavement response to subgrade moisture variations

Moisture has detrimental effects pavement structures. Moisture effects on different structures will vary depending on their dimensions and properties. In this study, sensitivity analysis of pavement response to moisture was conducted using multilayered elastic theory, based on arbitrarily assumed subgrade moduli and the moduli from literature sources, respectively. The selected simulation variables included elastic modulus and thickness of asphalt surface, base and subbase layers as well as axle load. The fatigue and rutting life as well as their sensitivity indexes were obtained for each scenario. The results show that the soil with a relatively higher plasticity generally resulted in a higher sensitivity, whilst this trend was not monotonic with the soil plasticity. Drainage implications were summarized to provide a reference for the pavement drainage design. A drainage design process was proposed by incorporating sensitivity analysis. This study will facilitate the understanding of pavement response under different subgrade moisture conditions and pavement drainage design.

Evaluation of the Effect of Interlayer Bonding Condition on the Deterioration of Asphalt Pavement

In this study, to investigate the effect of interlayer bonding condition on the deterioration of asphalt pavement, we conducted numerical analysis based on multi-layer elastic theory, verification of numerical analysis results by experiments on a full-scale test track, and comparison of the progress of deterioration based on accelerated loading tests conducted on the test pavement. Firstly, the analysis indicated that stronger tensile strain could occur on the upper side of the interlayer when the interlayer bonding weakens. Furthermore, the test pavement simulating interlayer debonding showed the same strain tendency as the analysis. These results suggest that if the interlayer debonding continues, the pavement may suffer early fatigue failure. On the other hand, there are some results that are not consistent with those of the analysis, such as the magnitude of deflection in the test pavement; thus, further investigation is required. Furthermore, because of the accelerated loading on the test pavement, the sections where the layers were debonded immediately after construction became bonded. Since the deflection of the test pavement did not change significantly from that immediately after construction, and no conspicuous damage such as cracks was observed on the road surface, it is considered necessary to continue follow-up surveys.

In-situ structural analysis of lightweight cellular concrete subbase flexible pavements

This study in Canada aimed to improve the performance of flexible pavements by comparing the in-place behavior of Lightweight Cellular Concrete (LCC) at three densities with traditional unbound granular material. The research investigated the effect of traffic load and testing temperature on pavement response and determined the structural layer coefficient for the 475 kg/m³ density. The structural layer coefficient for the LCC subbase at this density was 0.22. Results showed that pavements with LCC had over three times less stress at the top of the subgrade compared to the conventional granular material. The Weslea software, which uses a multi-layer elastic theory, appeared to overestimate stress responses for LCC pavements, and the research suggested a prediction modification for more accurate results. Overall, the study demonstrated that lightweight cellular concrete with different densities could improve pavement performance.

Structural Performance of Foamed Asphalt Base in a Full Depth Reclaimed and Sustainable Pavement

Environmental awareness and budgetary constraints in road construction and rehabilitation require innovative and at the same time environmentally friendly solutions in favor of resource conservation, in any type of pavement intervention. In the meantime, surface interventions in severely deteriorated pavements are insufficient, increasing as such the recycling potential of existing materials in Full Depth Reclamation (FDR). This study addresses the efficiency of an FDR process in which the recycled base course of an existing semi-rigid pavement is stabilized with Foamed Asphalt (FA). The adverse effects of FA curing, which have a significant impact on pavement evaluation, particularly in the early stages of a pavement’s life cycle, prompted the conduct of a comprehensive testing campaign at two different periods, shortly after pavement rehabilitation and five years thereafter. The campaign included nondestructive testing at the aforementioned periods using Ground Penetrating Radar (GPR) and the Falling Weight Deflectometer (FWD), which facilitate the structural evaluation of the FA base. Using the collected nondestructive testing data, the principles of Multi-Layer Elastic Theory (MLET) and Genetic Algorithms (GA) are used to investigate the performance of the FA base. Both analysis tools captured the FA strength increase in the second period, but an increased variance of the FA modulus was observed mainly in the first test period, probably due to the curing effect. In addition, GA showed an advantage over other, more conventional tools for back-analysis of pavement stiffness, resulting in an interesting correlation potential of FA modulus to a deflection-based parameter reflecting the condition of the FA layer. Overall, the study contributes to the development of a practical methodology suitable for the evaluation of non-conventional and sustainable pavement structures.

An Italian road pavement design method for bus lanes: proposal and application to case studies

In urban centres, the presence of bus lanes is essential to facilitate public transport services for a better sustainability of the cities and reduction of private traffic and pollution. However, bus lanes need a specific geometric (i.e. road layout) and structural (i.e. pavement layer thickness) suitable design. The pavement design of bus lanes in urban areas is often performed using traditional methods, already used for other types of roads. Given the geometric and structural peculiarities of each road in the urban centres due to the historical city development, the application of these methods can lead to an incorrect road pavement design.For this purpose, a first attempt of a road pavement design system has been developed for bus lanes: it is a specific catalogue proposal for this type of lanes, which can support the technicians in evaluating the most appropriate solutions in terms of materials and thickness, for both new construction and maintenance.After evaluating the types and main characteristics of buses circulating in Italy, traffic levels (in terms of equivalent standard axle loads), subgrade bearing capacity and pavement structure were hypothesized. Assuming three possible structures and five traffic levels, a total of forty-four design solutions were drawn up. The required pavement thickness varies from 17 to 47 cm for a new lane construction and from 9 to 22 cm for an existing lane maintenance.All the proposed solutions have been verified by methods and models based on multi-layer elastic theory available in the literature. Moreover, their validity was evaluated applying the solutions to real cases. The results of this work encouraged the authors to improve the catalogue inserting solutions with natural stone, particularly used in historic centres for architectural and aesthetical reasons, and to differentiate the pavement thickness of bus lanes subject to high stresses (intersections, stops, etc.).

Evaluation of the structural response of two in-service thin flexible pavements under heavy vehicle loading during different seasons by built-in sensors

ABSTRACT Long Heavy Vehicles (LHV) are considered more efficient and environmentally friendly transportation of goods compared to conventional trucks. Thus, the maximum allowable gross vehicle weight (GVW) in Sweden was increased on part of the road network from 64 to 74 tons in 2018 by increasing the vehicles’ length and the number of axle groups per vehicle but not the axle load limits. This change in loading conditions is expected to lead to changes in the structural response and degradation rate of thin pavements on the low-volume road network. To improve our understanding of thin pavements behaviour exposed to multiple axle loadings two thin pavement structures located in the north of Sweden were instrumented with road response and climate sensors. Four measurement campaigns were carried out within one year by in-situ stress and strain measurements from the built-in sensors as LHV passes over at normal speed. The recorded response was compared with numerical calculations based on multilayer elastic theory (MLET). Values of stresses and strains showed a generally good agreement with high values of coefficient of determination R 2 during different seasons when the asphalt stiffness values were adjusted based on temperature and granular layer stiffness values based on moisture.

Development of a Mechanistic Method to Obtain Load Position Strain in Instrumented Pavement

To study the in-situ response and performance of asphalt pavement, instrumenting pavement with a variety of sensors has become one of the most important tools in the field or accelerated load facilities. In the dynamic response collection process, engineers are more concerned with the load position strain of the pavement structure due to wheel wander. This paper proposes a method to obtain the load position and the strain at the load position when there is no lateral-axis positioning system based on multilayer elastic theory. The test section was paved in the field with installed strain sensors to verify and apply the proposed method. The verification results showed that both the calculated load position and load position strain matched the measured values with an absolute difference range of 5–60 mm, 0.5–2.5 με, respectively. The application results showed that the strain at the load position calculated by the proposed method had a good correlation with the temperature, as expected.

A mechanistic perspective for airfield pavements evaluation focusing on the asphalt layers’ behaviour

ABSTRACT The preservation of structurally sound airfield pavements is critical for the capacity of the air transportation network. As a standard practice, the design and evaluation of flexible airfield pavements are mainly based on the Multi-Layered Elastic Theory (MLET) in accordance with the Federal Aviation Administration (FAA) principles. However, Asphalt Concrete (AC) materials perform as temperature- and loading rate-dependent materials because of the viscous nature of asphalt binders. This in conjunction with the real moving loading conditions imply that the pavement analysis and evaluation outcome might be significantly different from what is assessed according to MLET. The research is concentrated on adopting a mechanistic framework for the assessment of airfield pavements considering both assumptions for AC material characterisation (i.e. elastic and viscoelastic). AC viscoelasticity is accounted as per the MEPDG suggestion for in-service pavements and an energy-based damage evaluation is performed based on the FAA recommendations. A thorough field experiment along an airfield runway pavement, including sample coring and non-destructive data, is organised to meet the research aim. Results demonstrate an applicable approach that seems to be conservative when AC is considered as a viscoelastic material. This is expected to profoundly affect the decision-making when managing airfield pavement infrastructure.

Evaluation of reliability index and probability of failure for the improvement of the Nigerian empirical mechanistic flexible pavement analysis and design system (Nempads)


 
 
 The aim of this work was to evaluate reliability index (RI) with respect to fatigue and rutting within the different seasons peculiar to Nigeria, in order to improve Empirical-Mechanistic flexible pavement design approach, using First Order Reliability Method (FORM). Flexible pavement design involves many uncertainties, variabilities, and approximations regarding the input parameters like material properties, traffic loads. Others include subgrade strength, drainage conditions, construction, compaction procedures and climatic factors such as temperature, rainfall, and snowfall, etc. The combination of the variances associated with input parameters contributes to components and system uncertainty, and this combination of variances can have a significant effect on the predicted performance of the pavement. Reliability in pavement design is introduced to consider these uncertainties. Layers thicknesses, material properties, and Equivalent Standard Axle Load (ESAL) were entered into a multi-layer elastic theory software, ELSYM-5, which in turn were used to calculate strains and stresses for different seasons. The results obtained were entered into Nigerian fitted transfer function distress models to compute allowable ESALS. Miner’s hypothesis theory equation was used to calculate the cumulative damage due to stress and strains generated. A Framework was generated for finding individual reliability index (RI), systemic reliability index (SRI), and probability of failure. The findings showed that Season I (Winter) recorded the highest component reliability index for fatigue (5.63 for Normal Distribution). Season II (Summer) recorded the lowest component reliability index (β) for rutting (5.4 for Normal Distribution). Season III (Spring) recorded the lowest component reliability index for fatigue (1.85 for Normal Distribution)
 
 

Simulation of autonomous truck for minimizing asphalt pavement distresses

The improvement of the pavement performance by different means is essential for the smooth movement of autonomous trucks (ATs). This study focuses on minimising the pavement distress by controlling vehicular loading distribution pattern (wander), traffic distribution on lanes (lane sharing) of a road, and limiting the running duration of AT to low-temperature time only. Mechanistic-Empirical Pavement Design Software, AASHTOWare, was incorporated in this research to analyze and then minimise the generation of asphalt pavement distress from autonomous truck loading. Different loading distribution patterns and traffic distribution of autonomous trucks were devised in AASHTOWare using the load equivalency factor (LEF) and lane distribution factors. Using multilayer elastic theory, LEFs were calculated for fatigue cracking and rutting separately. The acquired performances clearly showed significant improvement in pavement distress for a small increase of standard deviation of wheel wander and uniform distribution of traffic loading and for equally distributed ATs on the road lanes. In addition, an attempt has been made to optimise pavement distress in putting all ATs in a low-temperature duration of a day. Placing all ATs in a certain period of a day is beneficial for reducing asphalt pavement distresses and can bring a fruitful solution to prevent the early deterioration of the pavements.

APPLICATION OF ABAQUS PROGRAM TO INVISTIGATE THE EFFECT OF VARIATION IN SUBGRADE LAYER PROPERTIES ON THE DAMAGE OF FLEXIBLE PAVEMENT STRUCTURE

The major purpose of the pavement structure is to reduce stresses in the subgrades so that there is little or no deformation in the subgrade. Therefore, the more the subgrade is resistant to deformation, the thinner the pavement will be, thus reduction in the construction cost of the road. Finite Element techniques can be effectively applied to simulate different pavement problems that could not be modeled using the simpler multi-layer elastic theory. Thus, finite element Abaqus 6.14-1 program is used in this study. The laboratory tests are carried out on both the natural and stabilized soil samples that used as subgrade layer to determine the properties of subgrade that will be used as inputs for the finite element Abaqus program. The natural samples tested with three percentages of moisture contents (11.5%, 13.5%, and 15.5%). Different types of stabilizers are used in this study in form of mixture of two types of stabilizers. So, mixture of lime-kaolin (3%, 4%), mixture of silica fume-Poly Vinyl Alcohol (2%, 2%), mixture of Rice Husk Ash-Poly Vinyl Alcohol (3%, 2%), and 2% of silica fume are used as stabilizers. The pavement application by Abaqus program indicating that, the characteristics of subgrade layer have a big influence on the vertical deformation of whole pavement. The combination of (3% of Rice Husk Ash and 2% of Poly Vinyl Alcohol) as a stabilizer to the subgrade layer reduces the deformation about (9.5 %). While the addition of (3% of Lime and 4% of Kaolin) led to regard the deformation about (7.8%).

Determination of rutting performance of asphalt pavements considering realistic tire-pavement contact area

In the conventional pavement design procedure using multilayer elastic theory, tire loading equal to tire inflation pressure and traditional circular contact area are assumed. Therefore, the area of contact is extremely overestimated and the contact stress is significantly underestimated. Rotary Compactor and Wheel Tracker (RCWT) equipment was designed and fabricated with three different functionalities. The RCWT captures the realistic contact areas of pneumatic tires, simulates the field compaction process, and conducts simulative laboratory wheel tracking test. This study was conducted to determine relative damage of realistic tire-pavement contact area with respect to the traditional contact area. Based on the obtained footprint results, 63 percent difference exists between traditional and effective contact areas. Furthermore, it was found that based on the thickness of asphalt layer, vehicle tire was 2.5 to 1.5 times more damaging than full circular contact area. Moreover, realistic contact area causes about 50 percent reduction in pavement operational life.

Crosspave: a multi-layer elastic analysis programme considering stress-dependent and cross-anisotropic behaviour of unbound aggregate pavement layers

ABSTRACT This manuscript describes the development of a new pavement analysis programme called CrossPave based on the Multi-Layered Elastic Theory (MLET) framework, but capable of accommodating stress-dependent and cross-anisotropic behaviour of unbound pavement layers. Generally, Finite Element (FE) based programmes such as ILLI-PAVE, MICH-PAVE, SENOL, GT-PAVE etc. or general-purpose FE programs with special user-defined material sub-routines have been used to model the stress-dependent nature of unbound materials. However, these FE programme are time consuming and need certain expertise, making them unfavourable for implementation into practice. Few MLET-based programmes such as KENLAYER and Everstress are capable of considering the stress-dependent nature of unbound materials, but fail to accommodate some of the recently developed material models. The newly developed pavement analysis programme, CrossPave, addresses these issues, and incorporates five different non-linear stress-dependent resilient modulus models for unbound materials. Details of the developmental effort are presented in this manuscript, along with results from validation efforts highlighting close agreement between KENLAYER, ILLI-PAVE and GT-PAVE. Critical pavement response parameters for two full-scale pavement sections were calculated using CrossPave, and have been compared against field-measured values. The CrossPave programme has been presented as an enhanced, ready-to-implement programme compared to other MLET-based alternatives.

A mechanistic framework for field response assessment of asphalt pavements

Pavement analysis encompasses the use of different assumptions for material assessment that can in turn induce variations in the predicted pavement critical strains and affect the outcome of pavement evaluation. This research deals with the incorporation of mechanistic principles into asphalt pavements structural assessment, considering variable mechanical behavior (elastic and viscoelastic) for the Asphalt Concrete (AC) materials. A field experiment along a new asphalt pavement structure was performed including Non-Destructive Testing (NDT) and coring. The study focused on the tensile strains within the AC layers that usually trigger rehabilitation actions. For strain calculations, the standard practice of Multi-Layered Elastic Theory (MLET) and the rheological Huet-Sayegh model were both implemented into the analysis. Results indicated statistically significant discrepancies between elastic and viscoelastic calculations that may become considerable in terms of decision-making. Thus, pavement engineers should not proceed with the decision-making process based solely on a unique approach. In addition, the issue of performing a new pavement’s evaluation based on the desi gn assumptions was discussed. A substantial material differentiation pinpointed the need to extract cores in order to perform viscoelastic material characterization. Moving forward with a regression analysis, a practical approach was developed for viscoelastic strains prediction from NDT data in order to avoid extensive coring. Overall, the implementation of the framework at a new structure is grounded on that the methodology followed for pavement evaluation throughout its service life can predefine the way of decision-making in terms of consistently interpreting the analysis output and assessing future maintenance needs.

DETERMINATION OF DEFLECTION BASIN USING PAVEMENT MODELLING COMPUTER PROGRAMS AND FINITE ELEMENT METHOD

Several methods can be used to model pavement structures, namely multi-layered elastic theory (MET), finite element method (FEM), or finite difference method (FDM). In this study, three computer programs, KENLAYER and EVERSTRESS 5.0 which are based on MET, and ANSYS, representing the FEM, are used in Falling Weight Deflectometer (FWD) test on a pavement structure to determine deflection basin. The deflection basin was developed by using the results of vertical deflection from each sensor of an FWD test. In this study, a pavement structure was modelled for three locations of FWD tests, namely CH 200, CH 1450, and CH 2300. Based on the comparative study, all computer programs show good potential in determining deflection basin, with small percentage of Root Mean Square Error (RMSE) of between 1.00% to 4.31% for all models developed by the computer programs and field measurement. In order to obtain a higher accuracy of the FEM, the models considered the dynamic loading, increasing size of model geometry, as well as the reduction of the mesh element sizes. Moreover, changing from static to dynamic loading led to the reduction of percentage in RMSE for CH 200 from 2.41% to 0.94%. Decreasing size of closer elements of loading region also results in lower percentages of RMSE, calculated at 4.21% to 3.63% and 1.20% to 1.18% for CH 1450 and CH 2300, respectively. FEM, therefore, is found to be the best method for determining deflection basin of FWD in comparison to other MET computer programs.