# CBR Predictive Models for Granular Bases Using Physical and Structural Properties
## 3 Results  
In order to define which gravimetric and volumetric parameters have the largest influence on the values of CBR tests, dispersion graphics were used, and a tendency line was plotted for different parameters. This task was performed by plotting the coefficient R\({}^{2}\), which indicated the reliability or accuracy of the correlation. In other words, the more R\({}^{2}\) coefficient approached unity, the more reliable or accurate was the correlation. Table 4 summarizes the values of coefficient R\({}^{2}\) for each one of the volumetric and gravimetric parameters described in Table 3 with respect to the thirty-four CBR tests. It could be observed that the values of coefficient R\({}^{2}\) showed low values for all volumetric and gravimetric parameters of the soil. This means that not only a single parameter was influencing the CBR values but a combination of them. Also, different parameters affected CBR values, depending on the type of soil. For this reason, different equations were developed, depending on the type of material. Due to the nature of the soils tested, five groups of correlation analyses were performed for the different samples according to their classification: (1) samples with classification GW-GM and GP, (2) samples with classification SP, (3) samples with classification GW, (4) samples with classification GP, and (5) the combination of samples with classification GW or GP. Only these groups were created since the samples tested belong to such soil classifications. In order to develop other correlation analyses of materials with different soil classifications, it is necessary to perform tests on other materials with different graduation than those analyzed in this research. Table 5 shows the results of coefficient R\({}^{2}\) for the correlations, considering individually each one of the fourteen parameters for each group. Figure 2a-e shows these correlations. In general, the parameters presenting the largest correlations with the CBR test are the dry volumetric weight (\(\gamma_{\rm d}\)), the water content (w), and the void ratio (e). These correlations could be observed in Figure 2a. For materials GW-GM and SM, a linear relationship with \(\gamma_{\rm d}\) could be observed with R\({}^{2}\)= 0.83. For w, a polynomial correlation was observed with R\({}^{2}\) = 0.91. For e also, a linear relationship was observed with R\({}^{2}\) = 0.86. In the case of the materials SP, CBR values correlated linearly with parameters \(\gamma_{\rm d}\) with R\({}^{2}\) = 0.73; w with R\({}^{2}\) = 0.7; e and n with R\({}^{2}\) = 0.73. Also, for materials GW, CBR values correlated linearly with the following four parameters: (1) \(\gamma_{\rm d}\) with R\({}^{2}\) = 0.97, (2) \(\gamma_{\rm m}\) with R\({}^{2}\) = 0.79, (3) e with R\({}^{2}\) = 0.96, and (4) n with R\({}^{2}\) = 0.96. Figure 2c illustrates these correlations. Materials GP showed also linear relationships with the following parameters \(\gamma_{\rm d}\), e, and n with R\({}^{2}\) = 0.85 and \(\gamma_{\rm m}\) with R\({}^{2}\) = 0.71. These correlations are shown in Figure 2d. The combination of the materials with classification GW and GP showed correlations with parameters \(\gamma_{\rm d}\) with R\({}^{2}\) = 0.93; \(\gamma_{\rm m}\) with R\({}^{2}\) = 0.85; e and n with R\({}^{2}\) = 0.93. Such correlations are shown in Figure 2d. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \multirow{2}{*}{**Quarry**} & \multirow{2}{*}{**Sample**} & \multicolumn{8}{c}{**Gravimetric**} & \multicolumn{8}{c}{**Volumetric**} \\ \cline{2-13}  & & \(\gamma_{\rm s}\) & \(\gamma_{\rm d}\) & \(\gamma_{\rm m}\) & \(\mathbf{s_{\rm s}}\) & \(\mathbf{w}\) & \(\mathbf{C_{r}}\) & \(\mathbf{e}\) & n & \(\mathbf{G_{w}}\) & \(\mathbf{G_{a}}\) & \(\mathbf{\theta}\) & \(\mathbf{G_{C}}\) & \\ \hline
1–4 & 1–36 & 0.096 & 0.545 & 0.4 From the results summarized in Table 5, it could be observed that water content influenced the results of sandy soils (materials SP).