# Numerical Study of Geotextile-Reinforced Flexible Pavement Overlying Low-Strength Subgrade
## 3 Results and Discussion  
### Pavement Response  
The following cases were considered for the paved road: (1) unreinforced section, (2) reinforced at the base-subgrade interface, (3) reinforced at AC-base interface, and (4) reinforced at base-subgrade and AC-base interfaces. The results are presented in terms of permanent deformation and stress distribution in the pavement due to loading. Figure 3 shows the permanent deformation on top of the AC for the different cases considered for the paved section. Overall, the reinforced sections experienced lower rut depths than the unreinforced section; this is more pronounced on top of the subgrade, as observed in Figure 4. It is also notable that placement location and the number of geostynthetic reinforcement layers significantly influence the effectiveness of geotextiles in the pavement. Considering a single reinforcement layer, the section reinforced at the base-subgrade interface had lower permanent deformation than the pavement section reinforced at the AC-base interface, which achieved a percentage decrease of 6.5% compared to the unreinforced section. Increasing the reinforcement layers to two, as with the pavement section reinforced at the base-subgrade and AC-base interfaces, resulted in lower vertical displacement than all the trial sections, with a reduction of 25.2% compared to the unreinforced section. In summary, the reduction in rutting depth on top of the AC was 14.41%, 6.57%, and 25.2% for pavement sections reinforced at the base-subgrade interface, AC-base interface, and the double-layer reinforcement, respectively. Figure 4 presents vertical displacement curves from on top of the subgrade. It is observed that the benefits of geosynthetic inclusion in the flexible pavement system are more noticeable in the subgrade. The section reinforced at the base-subgrade interface achieved a decrease in vertical deformation of 51%, while that reinforced at the AC-base interface had a reduction of 41.2% compared to the unreinforced section. The double-layer reinforcement contributed to a 54.4% reduction in vertical deflection compared to the unreinforced section. The margin in reduction of permanent deformation on top of the subgrade, for the double-layer reinforcement and that of reinforcement at the base-subgrade interface, is relatively small. Figure 2: Comparison of load–displacement for the experimental work and the numerical simulation results for (**a**) unreinforced sections and (**b**) reinforced sections. Figure 5 shows stress distribution on the subgrade layer for the different cases of the paved section. Notably, stresses developed on the subgrade of the unreinforced section are higher than those in the reinforced sections. The placement of a single reinforcement layer at the base-subgrade interface resulted in a 92.1% reduction in stresses transferred down to the subgrade. The section with a geotextile placed between the asphalt concrete and the base decreased by 87.3% in terms of the amount of stresses transmitted to the subgrade compared to the unreinforced section. Double-layer reinforcement, i.e., at the base-subgrade and AC-base interfaces, had the lowest stresses induced on the subgrade, with a reduction of 92.7%. However, the margin was relatively small compared to single-layer reinforcement at the base-subgrade interface. A resulting implication is that increasing reinforcement layers in paved sections overlying soft subgrade may not necessarily increase its effectiveness by a higher margin in terms of absorbing stresses from traffic loading. The vertical displacement and stress distribution in the geotextile's plane are shown in Figure 6.  
Figure 4: Comparison of vertical displacement on top of the subgrade. Figure 3: Comparison of vertical displacement on top of the AC. Figure 5: Comparison of stress distribution on top of the subgrade. Figure 6: Cont.