الفهرس 
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Abstract
Researchers have devoted a great effort over recent decades to improve the structure design of flexible pavements. Flexible pavement design methods can be classified into methods based only on experience and typically used for the design local roads subjected to low traffic volumes, empirical methods with/without a soil strength, limiting shear failure method, limiting deflection method, empirical methods based on pavement performance or road tests, and Mechanistic-Empirical (M-E) methods. The current state of pavement design practice is largely relying on empirical methods of which the most widely used method is the American Association of State Highway and Transportation Officials (AASHTO) 1993 guide for pavement design. However, large databases now exist for traffic characteristics, site climate conditions, pavement material properties, and historical performance of in-service pavement sections. These and other assets provided the technical infrastructure that made possible the development of the Mechanistic Empirical Pavement Design Guide (MEPDG) under two important research projects, NCHRP Project 1-37A and NCHRP Project 1-40D. In this research project, a simplified M-E design method based on the principals of the NCHRP 1-37A, NCHRP -140D, and NCHRP 9-22 is developed. In the proposed method, the AASHTO 1993 design method is still used to design an initial pavement structure based on the user inputs (i.e., material properties “modulus”, traffic data “ESALs”, design reliability, and design criteria) or a trial pavement structure can directly be inputted instead based on the designer experience for further analysis. Then, the effective temperature predicted based on the climatic data, is used to adjust the dynamic modulus of the Hot Mix Asphalt (HMA) which has a significant effect on the anticipated AC rutting and alligator fatigue cracking distresses for a particular pavement structure and project location. After that, a Finite Element Analysis (FEA) module is used to compute the structural responses (e.g., stresses, strains, and deflections) at the critical locations within the pavement structure. Finally, these responses are converted into distresses (rutting, fatigue cracking and roughness) through the calibrated performance models for each distress type. The calibration of the performance models was conducted based on data form the Long Term Pavement Performance (LTPP). The LTPP sites for data collection were selected such that they represent similar climate to Egypt and the hot and moderate climatic areas rather than the cold areas. The proposed methodology was incorporated into a computer code and validated using numerous comparisons with current practices (AASHTO 1993, Multi-Layer Elastic Analysis (MLEA), and NCHRP 9-22). Based on the statistical analysis results, the proposed methodology despite the simplifications, it yielded acceptable prediction accuracy for the rut depth values compared to the current practices, while it showed better prediction accuracy for the fatigue cracking. In addition, based on the sensitivity analyses conducted on the pavement rutting and Asphalt Concrete (AC) “alligator” fatigue cracking, the AC rutting was found to increase by increasing ESALs, mix air voids, effective asphalt content (Vbe), tire pressure, and design reliability and decreasing AC stiffness and operating speed. However, base thickness and modulus, subgrade modulus, and wheel load had no significant effect on AC rutting. For thin AC layer; the increase of the modulus of AC layer, increases AC “alligator” fatigue cracking. Conversely, for thick AC layer, increasing the AC modulus yields a better AC fatigue cracking resistance. AC fatigue cracking decreased by increasing ESALs, base and subgrade modulus, and effective asphalt content (Vbe) of AC mix. Moreover, AC fatigue cracking increased by increasing AC mix air voids (Va). The base rut depth was found to increase by increasing the base thickness, wheel load, and design reliability and decreasing the AC thickness and base modulus. Subgrade rut depth decreased by increasing the AC thickness, base thickness, base modulus, and subgrade modulus, and decreasing the wheel load and design reliability. However, base and subgrade rut depths were not significantly influence by the AC stiffness, operating speed, and tire pressure. Finally, the proposed design methodology is recommended to be used for flexible pavement design in Egypt. The method yields yearly performance of the designed pavement system which will assist in providing a maintenance plan and estimating the life cycle cost of the system.