## 4 Evaluation of the Undrained Shear Strength Based on Empirical Relationships  
Evaluation of the undrained shear strength \(\tau^{\prime}_{fu}\) of overconsolidated and normally consolidated organic soils from dilatometer tests was carried out on the basis of single- and multi-factor empirical relationships proposed by [PERSON] (2011), [PERSON] (2010); [PERSON] et al. (2011), and [PERSON] (2013), as well as the three-factor relationship of [PERSON] (2013) using Equations (4)-(8), and empirical coefficients determined on the basis of the void ratio \(e\) from Equation (9). In order to compare the undrained shear strength evaluated based on empirical relationships with undrained shear strength obtained from field vane tests, the measurements from dilatometer tests were taken from the same depth where FVT was carried out. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & \multicolumn{4}{c}{**Maximum Relative Error Max \(RE\) of Evaluated**} \\  & & & \multicolumn{4}{c}{**Undrained Shear Strength \(\tau_{fu}\) (kPa) for:**} \\ \cline{3-6}  & & & \multicolumn{4}{c}{**Single-Factor Relationships by**} & \multicolumn{2}{c}{**Multi-Factor Relationship by**} \\ \cline{3-6}
**Sites** & **Soil Type** & & \multicolumn{4}{c}{**Modified**} & \multicolumn{2}{c}{**[PERSON] and**} & \multicolumn{2}{c}{**[PERSON] (2013)**} \\  & & & **[PERSON] (2013)** & **[PERSON] (2013)** & **[PERSON] (2013)** & **[PERSON] (2013)** & **[PERSON] (2013)** \\  & & & **Equation (5)** & & **Equation (7)** & & **Equation (8)** \\  & & & & \multicolumn{4}{c}{**max \(RE\)**} & \multicolumn{2}{c}{**max \(RE\)**} & \multicolumn{2}{c}{**max \(RE\)**} \\  & & & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline \multirow{4}{*}{\(\begin{array}{c}\text{{\text{{\text{{\text{{\text{{\text{\text{\text{\text{\text{ \text{ \text{ \text{ \  
For each relationship, the maximum relative error max \(RE\) (Table 6) for particular organic soil was selected from values of the relative errors \(RE\) calculated according to the formula:  
\[RE=\left|\left(d^{(p)}-y^{(p)}\right)/d^{(p)}\right|\cdot 100\%, \tag{11}\]  
where \(P\) is the number of cases, \(p\in\{1,\ldots,P\}\), \(d^{(p)}\) is the measured value, and \(y^{(p)}\) is the calculated value. Analysis of the calculation results indicates quite high maximum relative error values obtained for the undrained shear strength evaluated on the basis of the single-factor empirical relationship of [PERSON] ranging between 47.5-58.7% for peat, 27.6-50.0% for gyttija, and 48.4-50.8% for mud. The max \(RE\) values calculated for undrained shear strength evaluated from the [PERSON] et al. relationship with the bearing capacity factor \(N_{c}\) determined for organic soils are smaller, and range between 19.0-50.9% for peat, 7.2-40.6% for gyttija, and 7.7-21.5% for mud. The max \(RE\) values calculated for undrained shear strength evaluated from the [PERSON] and Houlsby relationship with the bearing capacity factor \(N_{D}\) determined for organic soils are slightly smaller, and range between 8.0-47.0% for peat, 4.8-31.3% for gyttija, and 12.0-17.0% for mud. The comparison carried out for the version of the [PERSON] relationship modified by [PERSON] for organic soils indicates that the max \(RE\) values obtained for the undrained shear strength of organic soils for the Antoniny, Koszyce, and Nielisz sites vary between 3.3 and 35.1%. The comparison carried out for the three-factor relationship of Rabarijoely, from which the empirical coefficients were determined on the basis of the void ratio, indicates much smaller max \(RE\) values of the undrained shear strength for peat at 0.9-13.4% and for gyttija at 7.2-12.1%. This shows that the evaluation of the undrained shear strength from dilatometer tests for the tested peat and gyttija from the three-factor relationship of Rabarijoely results in a better accuracy; however, it requires the use of empirical coefficients individually determined on the basis of the void ratio.