Alireza Bayat

Evaluation of the effects of Canadian climate conditions on the MEPDG predictions for flexible pavement performance

This study aims to investigate the quality of the recently developed Canadian climatic database and the effect of climatic factors on flexible pavement performance using the mechanistic-empirical pavement design guide (MEPDG). Two hundred and six Canadian climatic files were used to carry out the analysis. Freezing index and frost depth from the MEPDG were compared with the data available in Canadian databases. The sensitivity of pavement performance to climate conditions, predicted using the MEPDG, was also studied. The pavement performance predicted using the virtual weather station and existing weather station data was compared. From the pavement performance sensitivity study, it was found that the asphalt concrete, total pavement rutting and international roughness index show sensitivity to climate changes. It was also found that differences in the quality and duration of data for close-by stations can result in variation in the predicted performance. Overall, the study assists with facilitating the implementation of the MEPDG in Canada.

Compression Behavior of Large-Sized Tire-Derived Aggregate for Embankment Application

Tire-derived aggregate (TDA) has been successfully used for highway embankment applications in the past. Previous applications mainly used small and medium tire sizes as TDA sources. There are no published test results in the literature regarding the compression behavior of TDA made solely from off-the-road tires (OTR). In this study, large-scale, one-dimensional compression tests are carried out to study the compression behavior of TDA from OTR as well as from passenger and light-truck tires (PLTT). Samples for the tests are prepared by varying the initial unit weights. The results show that there is a general trend of decreasing compressibility with increasing initial unit weight for both TDA sources. The compression test results are also used to compare compression behavior between the two TDA sources. It is found that the compression behavior of TDA from OTR and PLTT is more or less similar. Moreover, one-dimensional stress-strain regression equations were developed for TDA from OTR.

Investigation of Hot-Mix Asphalt Dynamic Modulus by Means of Field-Measured Pavement Response

The current Mechanistic–Empirical Pavement Design Guide (MEPDG) proposes the use of the laboratory dynamic modulus test to determine time–temperature-dependent properties of hot-mix asphalt (HMA) materials. To date, limited measurements have been performed to compare the HMA behavior of laboratory dynamic modulus test with the field measured pavement response. The objectives of this study were to compare and validate laboratory-determined HMA dynamic modulus with field-measured asphalt longitudinal strains. Under constant loading frequency, the laboratory-determined dynamic modulus for Hot Laid 3 (HL3) was found to decrease exponentially when the temperature of the asphalt mix increased. Controlled wheel load experiments, performed at a constant truck speed, found that HL3 asphalt longitudinal strain increased exponentially with an increase in asphalt middepth temperature. The comparison of both exponential relationships showed that the laboratory-determined dynamic modulus was inversely proportional to the field-measured asphalt longitudinal strain.

Field monitoring and comparison of thermal- and load-induced strains in asphalt pavement

The influence of pavement temperature variations on field thermal-induced strains has not been well studied. Measuring the thermal- and load-induced strains in field conditions will assist in developing realistic pavement performance fatigue models. A field investigation programme was developed at the University of Waterloo to quantify thermal-induced strains in typical Eastern Canadian climate conditions. The main objective of this field study was to measure and compare the amplitude of load- and thermal-induced strains over a 1-year monitoring period. Results indicated that the average monthly thermal-induced strains were higher than the load-induced strains by a 49 kN wheel load moving at 25 km/h. Although the frequency of thermal-induced strains is lower than the traffic loads, damage from thermal-induced strains could be more than load-induced strains due to higher amplitudes.

One-dimensional compression model for tire-derived aggregate using large-scale testing apparatus

Abstract The engineering properties of tire derived aggregate (TDA) have been the subject of previous laboratory investigations; however, these investigations have been conducted primarily on TDA that is one-third the size of TDA used for engineering applications. In this study, the compression behavior of compacted TDA samples with a maximum particle size of 300 mm, typically used for engineering applications, has been investigated using custom-made testing apparatus designed to accommodate the large-sized TDA. Tire derived aggregate properties important to engineering applications, including compression behavior, the coefficient of lateral earth pressure at rest, and Poissons ratio, are provided, while variation in the gradation of TDA particles and the tire type for TDA production are experiment variables. This study also proposes a method to prepare compacted TDA samples for large-scale testing.

Investigation of tire derived aggregate as a fill material for highway embankment

Abstract This study investigates the compression behavior and performance of tire derived aggregate (TDA) used to construct an 80-m long embankment for a highway test road in Edmonton, AB, Canada. The road contained four test sections made from passenger and light truck tires (PLTT), off-the-road (OTR) truck tires, TDA–soil mixture, and native soil. A total of 30 temperature probes and 25 settlement plates were embedded into the road to monitor the embankment. Falling Weight Deflectometer (FWD) test was also conducted under different load levels to determine the embankment material’s deflection behavior after the placement of the soil cover. Through observation, field data, and FWD testing, it was determined that PLTT is more compressible than OTR and the TDA–soil mixture, and TDA–soil mix section showed equivalent performance with the control section. Additionally, all the temperature probes revealed no internal heating during the 8-month monitoring period.

Field evaluation and analysis of flexible pavement structural responses under dynamic loads

This study investigates the structural responses of flexible pavements at the Center for Pavement and Transportation Technology (CPATT) test track located at Waterloo, Ontario, Canada. A comprehensive field testing program was performed to examine flexible pavement responses to a variety of loading conditions. Tests were completed using six tire types: 11R22.5, 275/80R22.5, 295/75R22.5, and 285/70R22.5 dual tires, and 455/55R22.5 and 445/50R22.5 wide-base tires, and tire inflation pressures that ranged between 482 to 827 kPa. A two-dimensional finite element model was developed using MichPave software to predict pavement responses. A simplified method was proposed to characterize HMA properties using the laboratory dynamic modulus test. The developed model simulations approximated the field measured responses to all loading configurations.

Fluidic Drag Estimation in Horizontal Directional Drilling Based on Flow Equations

AbstractHorizontal directional drilling (HDD) is a trenchless technology used to install underground utilities. The force required to pull a pipe through the borehole during installation is crucial to design engineers. Various methods have been proposed to estimate the pullback load, each dealing with fluidic drag in a different way. Limitations in fluidic drag estimation by current design procedures have revealed the significance of having a reliable method for calculation. This paper proposes a new method to calculate fluidic drag based on annular flow equations. This method is used to calculate viscous drag for two HDD case studies, and the results are compared to the estimations by current methods, such as PRCI and ASTM F1962. Pullback load estimation based on the new method agrees well with the actual installation loads. This paper also investigates the impact of design factors on fluidic drag by presenting a sensitivity analysis over a practical range of related parameters. The ratio of pipe radius ...

Clogging potential of tunnel boring machine (TBM): a review

Tunnel boring machines excavating through soft soils face different challenges, one of which occurs when the soil sticks to the cutter face or the conveyor band and obstructs the machine. This phenomenon, commonly referred to as clogging, leads to wearing of the cutting wheel and transportation system, delays in the time schedule and economic loss. Although several laboratory devices can evaluate the adhesion mechanism of soil to metal, the method to measure adhesion has not been standardised. As clogging is also directly related to the construction phase, engineers are more concerned with methods to avoid this problem during construction. In this regard, the application of soil conditioners has become useful, the benefits of which include torque reduction, easier soil manageability and clogging reduction. However, the effectiveness of the soil conditioners is difficult to evaluate. To provide some insight into the topic, this paper describes the basic mechanism of clogging, the key parameters for its evaluation, the laboratory tests conducted up to date, the classification diagrams developed to assess clogging risk and mitigation of this risk in underground tunnelling. This paper also describes some of the additives and their functions, the ratios used for measurement and application, and the current tests to evaluate their performance. Finally, the conclusions summarise the current findings in the issue of clogging, pointing to the advantages and shortcomings of previous research, as well as some lines of investigation to improve identification and mitigation of this problem.

Mechanical properties of clayey soil relevant for clogging potential

Due to its advantages, including reduced operation time and cost, tunnelling with boring machines in urban areas has become a popular technique over hand-tunnelling or open-trench excavations. However, tunnelling in clayey soil poses a great challenge since the mechanical and physical properties of clays cause different issues, one of which is clogging. To solve this problem, engineers have treated the soils with different soil conditioners in order to change their rheological properties, improve their manageability and eliminate undesirable characteristics. However, the root of this problem is the lack of understanding the phenomenon and characterising it on the framework of soil mechanics. By considering the use of polymers, this paper aims to provide information regarding the theory involved in this mechanism and the factors influencing clogging potential. The authors present a systematic study of the physical and mechanical properties of plain soil and conditioned soil, which includes a direct shear test, vane shear test and Atterberg limits test. Results show that the initial water content, roughness of shear plate and percentage of additive have a significant effect on the clogging potential. Additionally, the results are plotted on an empirical diagram to understand the clogging potential by relating the clogging potential to soil properties.