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- Afridi, Muhammad Amjad
(författare)
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Municipal street pavement maintenance and management practices in Sweden
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A well-functioning street network is pivotal in the socio-economic development of a region. Street networks not only facilitate the movement of people and goods but also allocate space for utility services. Maintaining the street network in good condition and meeting the sustainability targets necessitate implementing optimal street maintenance strategies, leading to an efficient utilization of taxpayers' money. The objectives of this Licentiate thesis are to analyse pavement management practices and challenges faced by Swedish municipalities, specifically focusing on asphalt concrete (AC) pavements within street networks. Additionally, it seeks to integrate a sustainability tool into pavement maintenance to select maintenance measures that contribute to sustainability goals at the municipal street network management level. Furthermore, the study aims to enhance municipal-level pavement maintenance approaches through the implementation of machine learning (ML) models within a pavement management system (PMS). Within this context, three individual studies were conducted—two case studies and a survey involving Swedish municipalities. One case study explores sustainability framework application, whereas the other investigates the utilization of ML models in municipal AC pavement maintenance. The survey investigates the practices and challenges faced by municipal street network administrations in AC pavement maintenance.The sustainability framework SUNRA (Sustainability National Road Administrations) was adopted by the Swedish Transport Administration (STA) with a primary emphasis on promoting sustainability in pavement management on state-level roads. In this study, the framework has been tested, applied and further streamlined to be applicable for setting sustainability targets and monitoring sustainability performances at the project level within both the STA and municipal contexts. The aim was to simplify the framework so it is appropriate for investment, re-investments, maintenance and operation projects and also to enhance its applicability for various users. The study additionally explored how the framework could contribute to sustainability, identified the drivers and barriers for its application, and examined its applicability and adaptability to projects of varying complexities. The results indicate that the framework can be readily utilized and adapted for investment, reinvestment, maintenance, and operational pavement projects during the planning stage. Additionally, it is also suitable for small municipal establishments, construction or reconstruction of residential areas, and regular maintenance.A web-based questionnaire survey was disseminated to municipalities across the country to gather first-hand insights into the current practices and challenges associated with street maintenance at the municipal level in Sweden. Survey responses were received from 147 of the 290 (51%) municipalities nationwide. The study reveals that predominant pavement distress encompasses potholes, surface unevenness, and alligator cracking, with the most prevalent causes being pavement ageing, heavy traffic, and patches. Likewise, cold climate and population density serve as influential factors contributing to pavement deterioration. The automated survey methods for collecting pavement condition data, such as road surface scanning vehicles and application of commercial PMS, are very limited. On the contrary, the windshield method, a subjective approach for pavement condition assessment, is widely adopted among municipalities utilizing PMS. The allocation of the budget for maintenance, rehabilitation and reconstruction is higher in the northern regions of the country, as well as in densely populated municipalities.Manually collected pavement condition data for the years 2014 and 2018 were acquired from Skellefteå municipality to assess the performance of ML models in comparison to the observed pavement condition index (PCI) of the street network. In this context, the supervised ML models Linear Regression (LR), Random Forest (RF), and Neural Network (NN) were employed in conjunction with several variable combinations. The RF model, utilizing paired variables of pavement age (A) and pavement distresses (D) data, consistently demonstrated higher accuracy compared to the other models for residential streets. However, RF models constructed with paired variables of A and traffic (T) consistently outperformed other models in the context of non-residential streets. The significance of input variables fluctuates based on the model's complexity and the pavement performance objective. Nonetheless, variable A consistently emerges as the predominant factor for predicting PCI in both residential and non-residential street models. Further evaluation of the models and simplification of the SUNRA framework to enhance pavement performance and sustainability are recommended.
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| 2. |
- Larsson, Martin, 1982-
(författare)
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Cycle paths’ degradation processes and surface condition assessment
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A shift in modal share from car driving to cycling has many benefits, both from individual- and societal perspectives, e.g., better health from an increase in physical activity, lower levels of pollution and congestion. However, there are also some potential problems with such a shift. Cyclists have a higher risk of traffic incidents per travelled kilometre than car drivers. This risk needs to be minimized for an optimal transition to more cycling. A smooth surface with good friction on the cycle path is not only important for the traffic safety of the cyclists but also for their comfort and level of service. Potholes, cracks, and bumps are frequent obstructions on the cycle paths. These are all maintenance-related deficiencies associated with the degradation of the structure. In general, the knowledge on degradation of roads is good, as there is a long tradition of investigation into the degradation factors. Cycle paths, even though constructed with similar materials and techniques as the roads, are however not designed in the same way as roads, mainly since they will not be subjected to the same traffic load. Thus, one purpose of this licentiate thesis is to identify degradation factors specific for cycle paths, through a state-of-the-art literature study. This literature review is complemented by two papers, where Paper A analyses the distress found on Swedish municipal cycle paths and Paper B evaluates a novel method for condition assessments on cycle paths related to cycling comfort—the Bicycle Measurement Trailer. The review and papers are meant to act as the basis for the general aim of the PhD-project, namely, to develop more knowledge on the degradation of cycle paths. This knowledge is needed to improve the structural design approaches and maintenance strategies for cycle paths and to give guidance for preventive measures to inhibit degradation. A literature search in the national and international transport research databases was conducted, along with consultations in guidelines and handbooks on cycle infrastructure, in particular the official guidelines ofTrafikverket (the Swedish Transport Administration). Paper A is based on a state-of-practice survey in the Swedish municipalities where the stated distress modes and causes were analysed with respect to climatic and population data. The most common distress modes on municipal cycle paths in Sweden from previous studies—cracks, surface unevenness and edge deformation—were confirmed. The municipalities with main urban areas with a population of 60,000–120,000 habitants stand out from the general trend in that they seem to have less distress on their cycle paths. Further investigations are needed to find the main reasons behind this. For Paper B, field tests were conducted to establish the accuracy and repeatability of the proposed condition assessment tool, and the collected data was used to assess five different metrics for longitudinal evenness of cycle paths. The Bicycle Measurement Trailer was found to be a promising technique for condition assessment on cycle paths as it shows a high accuracy when compared to the standardized road measuring system, Road Surface Tester. The repeatability is also high. More studies are however needed to evaluate its ability to detect different distress modes. Such studies should proceed from the Evenness Coefficient metric. The conclusions of the thesis suggest that the structural design principles for cycle paths in present guidelines are insufficient for the optimization of the construction of cycle paths. They appear to be an adaptation of the structural design principles of low-traffic car roads rather than being developed specifically for cycle paths. The empirical-based models to calculate the estimated traffic load compared to the permitted traffic load are not accurate for structures with thin asphalt pavements (<75mm). Models that better describe the behaviour of thin asphalt structures, especially with respect to climate, should be developed. It should also be further investigated if the maximum load criterion is optimal with respect to the heavy vehicles that exert this load. The risk of damage to the structure from such extreme loads is at its highest when the load bearing capacity of the structure is at its lowest, i.e., the spring thawing period. More studies need to be conducted to determine the load bearing capacity of cycle path structures with different runoff and drainage conditions in this period of the year. The condition assessment manual Bära eller brista should also be updated with a section on root infiltration of cycle paths.
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| 3. |
- Saliko, Denis
(författare)
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Investigation of the structural response of pavements in cold region using instrumented test site data
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The structural behaviour of pavement structures is known to be affected by the traffic-related loading and by the ambient factors to which the structure is subjected. A new mechanistic-empirical (M-E) pavement design method is under development in Sweden with the main purpose to adequately predict pavement structural response and performance. An M-E design method for a flexible pavement means application of the principles of engineering mechanics to evaluate the response of pavement structure to traffic loading and much improved design methods to carry out distress prediction or how performance changes with time. This would ensure a fundamental understanding of how the pavement structure responds to a certain action or loading conditions. The mechanistic-empirical approach is more flexible as it is able to adapt to new situations such as new pavement materials and loading situations. It is important to take into account the real loading and climatic conditions and predict the resulting changes in material properties and structural behaviour at the time of loading as well as in the long-term. New models are therefore required for the further development of pavement design method, and it needs to be validated through reliable data obtained through realistic measurements.In this licentiate thesis, the effects of the environmental factors and loading by heavy vehicles in pavements are investigated. The results of the study are based on environmental data from multiple locations in Sweden and on measurements from two instrumented road sections located near the village of Långträsk in the northern part of Sweden. Both roads consist of thin flexible pavements, the behaviour of which is highly dependent on the variation of the temperature of the asphalt layer, the moisture content in the unbound granular layers, and frost depth conditions.The licentiate report consists of three scientific publications. Paper 1 presents a country-specific case study in which the frost penetration depth in various Swedish roads is predicted by a statistically derived empirical model that uses the air freezing index calculated from the air temperature as an input. The model correlation is based on meteorological data from 44 meteorological stations and pavement cross-sectional temperature distribution data from 49 road weather information system (RWIS) stations over all five climatic zones throughout all of Sweden.Paper 2 focuses on the response of an instrumented test section subjected to loading by falling weight deflectometer (FWD) and heavy vehicles. The mechanical response instrumentation consisted of asphalt strain gauges (ASG), strain measuring units (εMU), and soil pressure cells (SPC) installed at different locations in the structure. The layer stiffness values were obtained via backcalculation based on the FWD surface deflections bowls. The recorded values of the mechanical response were compared against calculated values by multilayer elastic theory (MLET) based software. Three different heavy vehicles weighing from ~64 tons to ~74 tons were compared in terms of damage caused to the pavement structure. It was found that if the number of axles was increased and dual tyres were used, longer heavier vehicles were not more destructive to the pavement structure than shorter vehicles with fewer axles and higher axial load and tyre pressure.In paper 3, the effect of the seasonal variation of the environmental factors on the behaviour of an instrumented road test section was investigated. The same loading configuration described in paper 2 was used on four different measurement campaigns in different seasons over the span of 1 year. The environmental variables were monitored throughout the year by asphalt thermocouples, a frost rod, and time-domain reflectometer (TDR) probes. The mechanical response sensors and the environmental sensors were found to be a reliable data collection method throughout the entire year. By comparing the recorded response values to the MLET calculated values, it was shown that it is possible to model the mechanical behaviour of pavement structures using linear-elastic MLET if the temperature variations in the asphalt layer and the moisture variations in the granular layers are taken into account.
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| 4. |
- Saliko, Denis
(författare)
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Validation of heavy vehicle loading responses and temperature predictions in flexible pavements using field data
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is well established that both traffic-related loading and environmental conditions influence the structural behaviour of pavements. Pavement design methods aim to consider the effect of traffic loading and environmental variables on pavement structure, foresee their changes during the lifetime of the pavement and predict the resulting distresses and pavement life. Newer models are required to further advance the development of pavement design methods. Validations using reliable and representative data are required prior to incorporating these models in pavement design methods.The impact of environmental factors such as temperature, moisture content and freeze-thaw cycles on pavement behaviour have been examined in this doctoral thesis. Furthermore, the impact of increased loading by new long heavy vehicles on low-volume roads subjected to large variations of the environmental conditions has been investigated. The findings presented in this thesis have been based on field data collected on roads that have been and currently are in day-to-day operation. The collected data on mechanical response, temperature, moisture and frost was used to validate models on mechanical behaviour and thermal behaviour, as well as the effect of their interaction in pavement structures. The models developed and validated in this study are aimed to be integrated into a new mechanistic-empirical pavement design framework that is currently under development in Sweden. The work done for this thesis is presented hereby in the form of 5 papers and a short summary part. This thesis is a continuation of a licentiate thesis previously published at KTH Royal Institute of Technology. Part of the material published in the licentiate thesis has been included in this doctoral thesis.In paper 1, air temperature data recorded over a span of 10 years from 44 meteorological stations and temperature data from built-in sensors in 49 pavement structures located in different locations throughout Sweden were analysed. The data was used to statistically correlate the freezing index, calculated using the mean daily air temperature and the frost penetration depth in the cross-section of the pavement. Comparisons were made for the results obtained for various climatic zones in the country. The output of the paper is a country-specific empirical chart obtained through exponential interpolation and nonlinear prediction limits that indicates a range of expected frost penetration depth based on historical air temperature data. Paper 2 presents a study in which the structural response of a test section was evaluated using built-in sensors. The instrumentation consisted of asphalt strain gauges (ASG) recording the tensile strain in the bottom of the asphalt layer, strain measuring units (εMU) recording the vertical strain in the granular layers, and soil pressure cells (SPC) recording the vertical stresses in the granular layers. Falling weight deflectometer (FWD) measurements were performed on the structure to backcalculate the stiffness of the layers from the measured surface deflections. The aim of the study was to evaluate the structural response of the structure under loading by three long heavy vehicles (LHV) weighing ~64 tonnes, ~68 tonnes, and ~74 tonnes and compare the resulting estimated accumulated damage from each vehicle. The main finding from the paper was that the damage caused to pavements by long heavy vehicles was slightly larger than the damage caused by shorter vehicles with fewer axles but higher axial loading and tyre pressure.Paper 3 focuses on the effect of environmental factors and their variation on the structural behaviour of a thin pavement structure. Loading by long heavy trucks was applied to a test section at four different measurement campaigns performed at different seasons over one year. The variation of temperature and moisture in the structure was monitored continuously for the entire duration for which the study was performed. Thermocouples embedded in the asphalt layer and a frost rod placed in the granular layers were used to monitor the temperature variation in the structure. The moisture variation was monitored using time-domain reflectometer (TDR) probes. The correlation of the changes in temperature and moisture to the changes in mechanical stiffness of the layers was investigated. The instrumentation used to monitor the mechanical response, temperature variation, and moisture variation in the structure was found to be reliable for collecting data over the entire duration of the study. The main finding of the study is that it is possible to model the mechanical behaviour of thin pavement structures using multilayer elastic theory (MLET) calculations modelling, using linear-elastic material models if the stiffness of the asphalt layer is adjusted based on temperature and the stiffness of the granular layers is adjusted based on moisture levels.In Paper 4, the same response testing procedure as in Paper 3 was performed for a second pavement structure with a thicker asphalt layer. Data from response testing results for 2 pavement structures on 4 different dates, with a focus on the spring thaw period, were considered in the paper. Three different strategies for material modelling were used to investigate the mechanical response of the pavement structures. The layers were initially modelled using linear material parameters and the response results were compared both to calculations in which a viscoelastic model was used for the asphalt layer and to calculations in which a nonlinear K-Theta model was used for the granular layers. Comparisons were made between the calculated response using each modelling strategy and the measured response values. It was found that the viscoelastic and nonlinear models provided only marginal improvements in the range of 1%-4% in predicting the mechanical response of the structures. Based on the results, it was concluded that the linear elastic model was sufficiently accurate in capturing the mechanical behaviour of both pavement structures, including at the critical locations.Paper 5 presents the development and validation of a one-dimensional finite control volume (FCV) model capable of predicting temperature in pavements. The model is intended to be implemented into a new mechanistic-empirical pavement design framework currently under development in Sweden. The model uses easily obtainable meteorological data for air temperature, solar radiation, and wind speed for the three main modes of heat transfer, namely conduction, convection and radiation. To validate the model and estimate its accuracy, comparisons were made between the measured temperature and the calculated temperature values, using the FCV model. Comparisons were made for the pavement surface temperature, the temperature within the asphalt layer, and the temperature in the granular layers for 4 pavements located in different climatic zones in Sweden. In general, good agreement was found between the measured and calculated temperature values. Points for future improvements include better consideration of the surface properties, including the latent heat transfer in the calculations, and coupling the model to a moisture transfer model.
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