## 4 Evaluation of the Soil Unit Weight Based on Laboratory Test Results  
The next step after performing laboratory tests was to search for the relationships between the dependent (soil unit weight \(\gamma_{t}\)) and independent variables (natural water content \(w\); organic matter content \(LOI_{T}\)). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & **Organic Content** & **Water Content** \(W\) & **Bulk Density** \(\rho\) & **Seili Unit Weight** & **Specific Density** & **Specific Density** \\  & \(LOI_{T}\) (\%) & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline Various organic soils & 5.02-84.93 & 23.52-417.91 & 1.17-2.25 & 10.27-19.86 & 0.23-1.82 & 1.52-2.59 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Index properties of organic soils at the Rzeszow site. Figure 8: Diagrams present the identification of organic soils based on CPTM tests, according to the propositions of [PERSON]’s nomogram. Figure 7: Diagrams present the identification of organic soils based on CPTM tests, according to the propositions of [PERSON] and [PERSON]’s nomogram. The one-factor relationship between the soil unit weight and natural water content is presented and described in the formula in Figure 9a and the organic matter content in Figure 9b. It has been shown that there is a very strong relationship between the variables included, as evidenced by the high value of the coefficient of determination \(R^{2}\), for natural water content (0.978) and only slightly lower for organic matter content (0.946). The differences between the values of the soil unit weight, calculated separately for each of the variables, with the value determined in a laboratory, were comparable. In the case of the first variable--natural water content--the max. difference was 21.76%, and for the second variable--soil matter content--the max. difference was 20.46%, in relation to the expected value of the soil unit weight. Additionally, based on the regression analysis, the relationship between empirically determined values of soil unit weight and leading parameters (natural water content and organic content) was determined and is described by the following formula:  
\[\gamma_{t}=17,4603+0,0407 LOI_{T}-0,0307w \tag{4}\]  
where \(\gamma_{t}\) is the soil unit weight, \(LOI_{T}\) is the organic content and w is the natural water content. The differences between the values determined on the basis of laboratory tests and the model determined by the regression method, taking into account two variables, did not exceed 2.95 kN/m\({}^{3}\) (22.44%), with the factor \(R^{2}\) = 0.797. Variable significance studies (\(w\), \(LOI_{T}\)) were conducted and showed that the variable representing the organic content was not significant. After eliminating the insignificant variable, it was found that the differences between the set value and the expected volume of the soil unit weight were much higher at 3.96 kN/m\({}^{3}\) (38.00%), in comparison to the case of the model with two variables. Due to the larger differences and the fact that the model with one explanatory variable was not very representative, the model with two variables was adopted for further analysis. The comparison of the results is presented in Figure 10.  
For the analytical estimation of the soil unit weight, personally determined one and two-factor relationships were used; therefore, it was necessary to determine the value of the relative error in the relationships in relation to the values determined empirically in the laboratory. The maximum and minimum values of relative error were calculated according to Formula (5):  
\[RE=\left|\frac{d_{p}-y_{p}}{d_{p}}\right|100\% \tag{5}\]  
where \(P\) is number of cases, \(p=\{1,\ldots\,P\}\), \(d_{p}\) is the measured value and \(y_{p}\) is the calculated value. Figure 9: The value of the soil unit weight estimated from laboratory tests was in reference to (**a**) natural water content and (**b**) organic matter content.