| 1. |
- 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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| 2. |
- Erlingsson, Sigurdur, 1960-, et al.
(författare)
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Correlating Air Freezing Index and Frost Penetration Depth : A Case Study for Sweden
- 2020
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Ingår i: Lecture Notes in Civil Engineering. - Cham : Springer. ; , s. 847-857, s. 847-857
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The determination of frost penetration is one of the main requirements in considering environmental effects in pavement design in cold regions. At the present time, the frost depth of pavements in Sweden is estimated computationally using computer software which approximates the heat equation by finite difference. Due to the geographical positioning of Sweden, a wide range of air freezing index and frost penetration depths were observed with lower values in the south and higher values in the north. This paper introduces a simplified design chart which is obtained by empirically correlating the air freezing index estimated from temperature measurements by 44 local meteorological stations to the maximum frost penetration depth obtained by 49 RWIS Road Weather Information Station data. The results are classified depending on their location and the climatic zones defined by the Swedish pavement design codes. Nonlinear prediction intervals are implemented to provide a range of possible frost penetration depths since local site conditions are not taken into account. Further research is required to consider local on-site effects such as frost susceptibility of pavement materials, the thermal conductivity of layers, access to water and snow covering.
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| 3. |
- Everton, José, et al.
(författare)
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Freeze-thaw influence on the water retention capacity of silty sand subgrades
- 2022
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Ingår i: Proceedings of the 11th International Conference on the Bearing Capacity of Roads, Railways and Airfields. - London : CRC Press. - 9781003222897 ; , s. 122-131
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Konferensbidrag (refereegranskat)abstract
- Fine-grained materials are associated with a higher water retention capacity due to their higher surface energy in comparison with coarser materials. That characteristic is connected to why fine-grained materials also yields more suction when drying. In addition, seasonal variation of the water table subjects fine-grained subgrades to different moisture contents, varying the suction built in the subgrade, consequently affecting its mechanical characteristics. As fine-grained materials are frequently frost susceptible, they can cause issues to the whole pavement cross-section related to Freeze-Thaw (F-T) actions, widely known as frost heave and thaw weakening. This study will seek to investigate if subsequent cycles of closed-system F-T can permanently alter the unsaturated behaviour of fine-grained materials, using as background their Soil Water Retention Capacity obtained using a pressure plate apparatus. Such issues may become more common with permafrost areas being subjected to freeze and thaw cycles due to climate change or extraordinary events creating the circumstances to F-T where it is currently not observed. Two silty sands with low plasticity were tested, and the results show a reduced water retention capacity (WRC) after closed-system F-T cycles. Considering that matric suction changes the state of stress of soils, the findings suggest an impact in the resilient modulus (Mr ) not only seasonally, as it is well established, but also after seasonal freezing and thaw events.
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| 4. |
- Saliko, Denis, et al.
(författare)
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Damage investigation of thin flexible pavements to Longer Heavier Vehicle loading through instrumented road sections and numerical calculations
- 2021
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Ingår i: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402.
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Tidskriftsartikel (refereegranskat)abstract
- Longer Heavier Vehicles provide an improvement in energy efficiency and environmental performance compared to traditional Heavy-Duty Vehicles. In Sweden, the maximum permissible vehicle gross weight has been increased from ∼64 to ∼74 tonnes without increasing the axle load limits. The consequence of this is investigated in this study. Response from two instrumented thin flexible pavements subjected to loading from three types of heavy vehicles (∼64, ∼68 and ∼74 tonnes) has been measured and the recordings were compared with numerical calculations based on 2D multilayer elastic calculations. Pavement damage contribution by the three vehicles was thereafter investigated. As long as the number of axles is increased to compensate for the increased vehicle loading and dual wheels are used, ∼74 tonnes vehicle are not more aggressive to the two thin pavement structures compared to the lighter vehicles with fewer axles but higher average axle loads and tyre pressure.
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| 5. |
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| 6. |
- Saliko, Denis, et al.
(författare)
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Development and validation of a pavement temperature profile prediction model in a mechanistic-empirical design framework
- 2023
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Ingår i: TRANSPORTATION GEOTECHNICS. - : Elsevier BV. - 2214-3912. ; 40, s. 100976-
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Tidskriftsartikel (refereegranskat)abstract
- An accurate temperature prediction tool is an important part of any mechanistic-empirical (M-E) pavement design and performance prediction method. In this paper, a one-dimensional finite control volume (FCV) model is introduced that predicts the temperature within a pavement structure as a function of time and depth. The main input data required for the model are continuous time series of air temperature for conductive heat transfer, solar radiation for radiative heat transfer, and wind speed for convective heat transfer. The heat balance equation for each control volume of the FCV model is solved using an implicit scheme. To validate the numerical model, comparisons were made to measured temperature data from four test sections in Sweden located in regions with different climatic conditions. A good agreement was obtained between the calculated and measured temperature values within the asphalt layer, and temperature in the granular layers with the values of the coefficient of determination R2 ranging from 0.866 to 0.979. The model is therefore suitable to be implemented as a pavement temperature prediction tool in M-E design.
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| 7. |
- Saliko, Denis, et al.
(författare)
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Evaluation of the structural response of two in-service thin flexible pavements under heavy vehicle loading during different seasons by built-in sensors
- 2023
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Ingår i: The international journal of pavement engineering. - : Taylor & Francis. - 1029-8436 .- 1477-268X. ; 24:2
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Tidskriftsartikel (refereegranskat)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.
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| 8. |
- 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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| 9. |
- Saliko, Denis, et al.
(författare)
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Seasonal Variation of the Structural Response of a Thin Instrumented Flexible Pavement under Heavy Vehicle Loading
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The seasonal variations of the climatic factors such as temperature, moisture, and freeze-thaw cycles are known to influence the material properties and structural behavior of flexible pavement structures. Mechanistic models are required to predict the behavior of the structure throughout the entire year including the winter frost and spring thaw periods. In this study, the mechanical response of an instrumented flexible pavement structure located in the north of Sweden has been investigated at four different times during a year under loading by falling weight deflectometer and three different long heavy vehicles (~64, ~68 and ~74 ton). The mechanical response values recorded by the sensors embedded in the structure have been compared to the numerical model values obtained by 2D multilayer elastic calculations. It is shown that multilayer elastic theory provides a reasonable prediction of the mechanical behavior on the condition that the stiffness of the asphalt concrete is adjusted according to the temperature variations of the layer and the stiffness of the unbound granular layers is adjusted according to moisture content levels.
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