# Numerical Study of Geotextile-Reinforced Flexible Pavement Overlying Low-Strength Subgrade
## 3 Results and Discussion
### Effect of Reinforcement on Base Course Thickness  
Trials were conducted using the unpaved model reinforced at the base-subgrade interface to determine the potential and extent of base course thickness reduction due to geotextile reinforcement. The magnitude of vertical deformation at the top of the subgrade and base was analyzed. Similarly, stress distribution on the subgrade was analyzed.  
Base Course Reduction factor (BCR) was used to quantify the reduction in base layer thickness resulting from reinforcement. It describes the extent of reductions in aggregate base thickness allowed for equivalent service life. BCR is defined as the percentage decrease in base layer thickness due to the inclusion of geosynthetic reinforcement material in the unreinforced section under the same material composition and loading conditions. It is expressed as shown in Equation (2).  
\[BCR=\frac{B_{u}-B_{r}}{B_{u}}\times 100 \tag{2}\]  
where:  
\(B_{u}\) is the thickness of the base layer of unreinforced pavement.  
\(B_{r}\) is the thickness of the base layer of reinforced pavement.  
Figure 9 presents the variation in the magnitude of vertical displacement in relation to base course thickness for the unpaved section. The unreinforced section with a base thickness of 300 mm was taken as the control section. Six numerical simulations were performed, with the base thickness of the reinforced section being varied. The overall vertical displacements for the base and subgrade and the stresses on the subgrade were analyzed.  
As observed in Figure 9, the vertical displacements of the reinforced sections at the top of the base with thicknesses of 300 mm, 275 mm, 250 mm, 125 mm, and 210 mm were lower than the control section. However, the reinforced sections with 205 mm, 200 mm, and 175 mm base thickness had higher vertical displacement than the control section. Based on rut depth, this observation implies that it is possible to reduce base course thickness via geotextile reinforcement. From the study, the reduction in base thickness represents a BCR of 30%. The significant decrease in base thickness while maintaining the sound structural integrity of the pavement points out the potential saving of base course material. This is  
Figure 8: Comparison of stress distribution on top of the subgrade for geotextiles of varying elastic modulus.  
important since the quality material for pavement construction is limited and has posed challenges in road construction.  
The study findings on the reduction in permanent deformation are generally in agreement with the previous numerical evaluation conducted by [35]. It is worth noting that there are variations which can be attributed to the difference in reinforcement configuration and the type of loading applied. In the numerical study carried out by [1], the findings suggest that placement of reinforcement at the base-subgrade interface yields more reinforcement benefits, which is in line with our current study in terms of single-layer reinforcement. However, in this current study, a section with double-layer reinforcement was also simulated and placement of reinforcement at the base-subgrade and AC-base interfaces was more effective in reducing permanent deformation and stress absorbed by the subgrade.