## 1 Introduction
Table 1 summarises information from the literature on RL-CBR and the test conditions adopted, namely the base standard used (for the standard CBR test), mould dimensions (diameter; height), plunger diameter, the number of load cycles carried out, the axial displacement rate applied, the inclusion or not of a soaking phase of the specimens before testing, the penetration depth, the number of load stages, and the minimum stress reached in the unloading phase. The maximum load corresponds to the load required to achieve the penetration depth that represents the criterion for terminating the standard CBR test phase. Mechanical properties, such as the resilient modulus (M\({}_{\rm r}\)) and the equivalent modulus (E\({}_{\rm equ}\)), can be obtained through cyclic triaxial and RL-CBR tests, respectively [2; 7; 12]. The resilient modulus (M\({}_{\rm r}\)), which is another quantity frequently utilised in road design, is the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Reference** & **[PERSON] et al. [13]** & **[PERSON] [12]** & **[PERSON] et al. [6]** & \begin{tabular}{c} **[PERSON]** \\ **et al. [7]** \\ \end{tabular} & \
\begin{tabular}{c} **[PERSON]** \\ **et al. [2]** \\ \end{tabular} &
\begin{tabular}{c} **[PERSON]** \\ **et al. [14]** \\ \end{tabular} \\ \hline Base test standard & EN ISO & EN ISO & EN ISO & EN 1997-2: [16] & AS & EN ISO \\  & 13286-47 [15] & 13286-47 [15] & 13286-47 [15] & 12899.6.1.1 [17] & 13286-47 [15] \\  & 250; 200 & 250; 200 & 250; 200 & - & - & 152; 117 \\  & 81.5 & 81.5 & 81.5 & - & 49.6 \(\pm\) 0.1 & 50 \\  & 60–100 & 100 & 50–100 & 50 & 200 & 200 \\  & 1.27 & 1.27 & 1.27 & 1.27 & 1.27 & 1 \(\pm\) 0.2 & 1.27 \\  & - & - & - & No & Yes & - \\  & 2.54 & 2.54 & 2.54 & 2.54 & 2.54 & 2.54 \\  & 1 & 1 & 1 & 3 & 1 \\  & 0.1 & 0.1 to 0.2 & 0.1 & 0.01 & 0.05 & 0 \\ \hline \hline \end{tabular}  
* (d; h) = (diameter; height). ** Criterion for terminating the standard CBR test phase.  
\end{table} 
Table 1: Summary of RL-CBR procedures emerging from the literature review carried out (no information is included when the base reference does not describe the corresponding element). ratio between the axial deviatoric stress (\(\sigma_{\text{d}}\)) and resilient axial strain (\(\epsilon_{\text{a}}\)) (Equation (1)), and it is typically quantified using cyclic triaxial tests [7]. The equivalent modulus (E\({}_{\text{equ}}\)) represents an average response of the material in the mould, macroscopically, and is obtained by measuring the load and deformation during the loading and unloading cycle time of RL-CBR [12]. [PERSON] et al. [12] proposed Equation (2) to estimate the equivalent modulus from RL-CBR. This equivalent elastic modulus (E\({}_{\text{equ}}\)) depends on the following: Poisson's ratio of the soil, \(\upsilon\); change in the stress applied through the plunger in a loading cycle (difference between the maximum and minimum applied load), \(\Delta\sigma_{\text{p}}\) (MPa); radius of plunger, r (mm); change in elastic displacement in a loading cycle, \(\Delta\text{u}\) (mm). Instead of referring to the resilient modulus of the material, the equivalent modulus is used to represent the stiffness of the unbound material [12]. However, presently, the equivalent modulus cannot be used directly in pavement design, since the loads and stresses applied in the test are higher than typical traffic loads. Therefore, it is necessary to correlate the results of a triaxial test (under the same test conditions) to estimate the corresponding resilient modulus [12]. Given that developing countries tend to have unpaved roads carrying a large number of vehicles [6], it is critical to define a test procedure to estimate relevant mechanical properties of unbound materials using less expensive equipment and test protocols that are simple to implement and of simple interpretation. In this context, the RL-CBR test is more adequate, affordable, and accessible than the triaxial test [7].