THESIS ABSTRACT

Abstract

The performance of flexible pavements is increasingly challenged by heavier axle loads, growing traffic volume, and premature distress, particularly in roads constructed on weak subgrade soils. In response to these challenges, this study investigates the structural behavior of geocomposite- reinforced flexible pavement using three-dimensional finite element analysis in PLAXIS 3D. The pavement model consisted of a bituminous surface course, granular base, granular sub-base, and subgrade, developed in accordance with Department of Roads guidelines. The study examined the influence of geocomposite placement at different interfaces, i.e., asphalt concrete-base, subbase-base, and subgrade-subbase. In addition, the effect of geocomposite axial stiffness was evaluated using five different stiffness values under static loading conditions. Pavement performance was assessed in terms of vertical compressive strain at the top of the subgrade, tensile strain at the bottom of the bituminous layer, service life ratio for rutting and fatigue, and comparative construction cost. The analysis showed that geocomposite reinforcement significantly improves pavement performance compared with the unreinforced section. Among the placement configurations considered, the SG-SB interface was identified as the most appropriate because it provided the best combined response for both rutting and fatigue. For rutting control, this placement produced the lowest vertical compressive strain at the top of the subgrade, while for fatigue control it also improved the tensile response at the bottom of the bituminous layer. The influence of geocomposite axial stiffness was then evaluated at CBR 5%, 10%, and 15%. The results showed that increasing axial stiffness improved rutting resistance, with the highest stiffness value providing the best rutting performance, while its effect on fatigue response remained almost unchanged. The service life ratio analysis confirmed that reinforcement was most effective in weak subgrade conditions. Rutting-based SLR values of 2.58, 2.53, and 2.50 were obtained for CBR 5%, 10%, and 15%, respectively, while fatigue-based SLR remained 1.08 for all three CBR values. The cost analysis indicated that geocomposite-reinforced pavement requires a higher initial investment than unreinforced pavement, with the total cost increasing by about 24% for a 1 km road section, but it was justified by the improved structural performance and longer service life. Geocomposite reinforcement is therefore a practical and effective approach for improving the structural performance, durability, and efficiency of flexible pavements, particularly under weak subgrade conditions.

Keywords

Flexible pavement, geocomposite reinforcement, PLAXIS 3D, finite element method, service life ratio.