## 5 Test Results and Discussion
### The Variation of Elasticity Modules after Traffic Loading  
The PLT can be carried out using different methods, depending on the required information. These methods include: (1) determining the initial tangent modulus; (2) assessing the tangent modulus at a specific stress level; (3) determining the reloading and unloading modulus; and (4) determining the secant modulus at a specific stress level. In all cases (test series I-II), a load-displacement curve following the general relationship shown in Figure 10 will be obtained. It is known that the influence depth of the PLT is about two times its diameter. Given that the thickness of the base/subbase layer is 450 mm, it can be observed that the influence zone of the PLT (with a diameter of 300 mm) extends to the underlying layer. Hence, the modulus derived from PLT represents the combined modulus rather than the actual modulus of the tested layer. In this research study, the initial tangent modulus (the composite modulus) (E\({}_{\text{PLT}}\)(1)) and the reloading elastic modulus for the  
Figure 8: The change of displacements for granular fill section. Figure 9: Comparison of displacements for test sections: (**a**) total displacement, (**b**) permanent displacement. second and fifth load cycles (E\({}_{\text{PLT}}\)(i)) were determined from the PLTs using the following equation [38]:  
\[\text{E}_{\text{PLT}}(\text{n})=\frac{2\text{P}\big{(}1-\text{v}^{2}\big{)}}{\pi \text{R}\delta} \tag{1}\]  
where P is the applied load; R it the radius of plate; \(\delta\) is the deflection of plate at load, P; and v is the Poisson ratio, 0.3, in this study. The comparison of E\({}_{\text{PLT}}\) values obtained from the plate loading test for the N\({}_{\text{PLT}}\) = 1 cycle case for sections stabilized with rock fill and reinforced with geosynthetics compared to the unreinforced section is presented in Figure 11a. Additionally, a comparison of the same test sections for N\({}_{\text{PLT}}\) = 1-2 and 5 cyclic plate loading tests-repetition situations is given in Figure 11b. The findings showed a clear difference between the section stabilized with rock fill and other test sections for the N\({}_{\text{PLT}}\) = 1 cycle case. Nevertheless, as the plate loading number increased (N\({}_{\text{PLT}}\) = 1-2-5), there was also a significant increase in the elasticity modulus in the sections reinforced with geosynthetics. The unreinforced section (granular fill layer) did not show an increase similar to reinforced sections. The best performance was obtained from the section stabilized with rock fill. The dimensions of the rock particles were specially selected with an average size of 30 cm. In addition, in order to minimize the voids between the rocks, the voids were filled with granular material. In this way, a uniform, rigid rock fill layer was obtained. It enabled the rock fill layer to spread the applied load over a larger area, reducing displacements and, therefore, having a higher modulus of elasticity. The relationship between the modulus of elasticity of the sections stabilized with rock fill and reinforced with geosynthetics by the modulus of that same granular fill is called the modulus improvement ratio (MIR), determined from the E\({}_{\text{PLT}}\) values using the following equation [39]:  
\[\text{MIR}=\frac{\text{E}_{\text{PLT}}(\text{section stabilized or reinforced})}{ \text{E}_{\text{PLT}}(\text{granular fill})} \tag{2}\]  
The MIR values calculated for N\({}_{\text{PLT}}\) = 1 are shown comparatively in Figure 12a. Additionally, the MIR values obtained in the N\({}_{\text{PLT}}\) = 1-2-5 case are presented in Figure 12b. For the first plate loading test (N\({}_{\text{PLT}}\) = 1), in the case stabilized with rock fill, the MIR value was approximately 59% higher than in the granular fill section, while this rate was 15% in the section reinforced with geocell. It can also be seen that the elasticity modulus improvement ratio (MIR) is approximately 2% greater for single geogrid and 5% greater for double geogrid compared to the granular fill section.