## 6 Conclusions  
The analysis carried out for Pleistocene and Pliocene clays indicates that the evaluated undrained shear strength \(\tau_{fu}\) from the dilatometer test on the basis of single-factor empirical relationships: [PERSON], [PERSON] et al., and Smith and Houlsby gives quite high values of the maximum relative error max \(RE\) from 43% up to 48%. The two-factor relationship of Galas presented somewhat smaller values of the max \(RE\) up to 34%. From the single-factor empirical relationships the Smith and Houlsby relationship and from the multi-factor relationships the [PERSON] relationship gave better accuracy with the mean value of relative error \(RE\) at about 12% and 13%, respectively. So far the shear wave velocity \(V_{s}\) as an independent variable was not used to evaluate the undrained shear strength from the dilatometer test. The normalized undrained shear strength \(\tau_{fu}\)/\(\sigma^{{}^{\prime}}v\) in Pleistocene and Pliocene clays from the seismic dilatometer test (SDMT) can be evaluated using the proposed two-factor relationship based on the normalized difference between the corrected second pressure reading and the corrected first pressure reading \((p_{1}-p_{o})\)/\(\sigma^{{}^{\prime}}v\), and the normalized shear wave velocity \(V_{s}\)/100. The proposed relationship provides the evaluation of the normalized undrained shear strength \(\tau_{fu}\)/\(\sigma^{{}^{\prime}}v\) in Pleistocene and Pliocene clays from the seismic dilatometer test with a maximum relative error at about \(\pm 20\%\) and with the mean value of relative error \(RE\) at about 8%. Further research is needed for different types of cohesive soils with a higher variability of the plasticity index \(I_{P}\), consistency index \(I_{C}\), and stress history to verify empirical coefficients determined in this study. [PERSON] prepared the research program, performed the SDMT tests, analyzed the test results, and prepared the manuscript. [PERSON] prepared the research program, analyzed the test results and prepared the manuscript. [PERSON] performed the statistical analysis and prepared the manuscript. This research was funded by the Polish Ministry of Science and Higher Education. This work was carried out in cooperation with the partners from the Warsaw University of Life Sciences, Warsaw, Poland and the Bialystok University of Technology, Bialystok, Poland and was supported by the Polish Ministry of Science and Higher Education. A seismic dilatometer was used in the research purchased as part of the project \"Water Center\" of the Faculty of Civil and Environmental Engineering at the Warsaw University of Life Sciences implemented under the Operational Program Infrastructure and Environment, Measure 13.1, priority XII in 2010. The authors declare no conflict of interest. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Sites**} & \multicolumn{2}{c}{**Measured Values \(\tau_{fu}\)/\(\sigma^{{}^{\prime}}v\)**} & **Predicted Values \(\tau_{fu}\)/\(\sigma^{{}^{\prime}}v\)** & **Relative Errors of Individual** \\  & & **from CIU TT (\(\triangle\))** & **Equation (22) (\(\triangle\))** & **Case \(RE_{P}\) (\(\triangle\))** \\ \hline \multirow{5}{*}{\(V_{s}\)} & & 2.382 & 2.134 & 10.4 \\  & & 2.232 & 2.228 & 4.1 \\  & & 1.780 & 2.143 & 20.4 \\ \cline{2-5}  & & 2.038 & 2.018 & 1.0 \\  & & 2.176 & 1.918 & 11.9 \\  & & 1.997 & 1.706 & 14.6 \\ \cline{2-5}  & & 1.800 & 2.076 & 15.3 \\  & & 1.789 & 2.056 & 14.9 \\  & & 2.158 & 2.023 & 6.2 \\ \hline \multirow{5}{*}{\(V_{s}\)} & & 1.463 & 1.490 & 1.9 \\  & & 1.209 & 1.149 & 4.9 \\  & & 1.342 & 1.210 & 9.8 \\  & & 1.103 & 1.196 & 8.5 \\ \hline \multirow{5}{*}{\(V_{s}\)} & & 0.853 & 0.847 & 0.8 \\  & & 0.803 & 0.851 & 6.0 \\  & & 1.011 & 1.059 & 4.7 \\ \hline \multicolumn{5}{c}{Max \(RE_{P}=20.4\%\)} \\ \hline \multicolumn{5}{c}{The mean of the marked values} & Mean Value of Max \(RE=13.2\%\) \\ \cline{1-1} \cline{2-5}  & & Mean Value of \(RE=8.5\%\) \\ \hline \hline \end{tabular}
\end{table}