## 3 Materials and Methods
### Test Procedure and Test Program  
We carried out undrained cyclic triaxial loading tests on the sandy silty clay samples with the use of the cyclic triaxial apparatus manufactured by GDS instruments (ELDyn). The Cyclic Stress Ratio was defined here as the ratio of the maximum cyclic deviator stress \(q_{max}\) to the initial confining pressure \(p^{{}^{\prime}}\!_{0}\). The cyclic loading parameters of the samples are presented in Table 2. The soil samples after compaction were installed in the triaxial apparatus chamber, and the saturation phase was conducted. We terminated the saturation when the Skempton parameter \(B\) was equal to 0.95, which was, from the technical point of view, seen as an indicator of full saturation conditions. From this point, we conducted the isotropic consolidation phase. During this phase, the pressure inside the triaxial apparatus chamber remained constant, and the leakage of pore water was measured. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Soil Sample No**} & \multirow{2}{*}{**Moisture Content, \(w\) (\%)**} & \
\begin{tabular}{c} **Dry Density, \(\rho_{d}\)** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & \multirow{2}{*}{**Void Ratio, \(e_{0}\) (-)**} & \multirow{2}{*}{
\begin{tabular}{c} **Shear Modulus,** \\ **G\({}_{max}\) (MPa)** \\ \end{tabular} } \\  & & & & \\ \hline
1.1 & 13.76 & 1.932 & 0.391 & 115.0 \\
1.2 & 12.81 & 1.972 & 0.358 & 110.0 \\
1.3 & 13.58 & 1.904 & 0.383 & 65.0 \\
1.4 & 12.77 & 1.984 & 0.324 & 131.0 \\
1.5 & 13.58 & 1.948 & 0.366 & 155.0 \\
1.6 & 13.49 & 1.897 & 0.387 & 63.0 \\
1.7 & 13.27 & 1.892 & 0.370 & – \\
1.8 & 13.81 & 1.797 & 0.390 & – \\
1.9 & 15.53 & 1.841 & 0.332 & 62.0 \\
1.10 & 16.37 & 1.935 & 0.323 & 120.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Soil index properties for the samples in cyclic triaxial test. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Soil Sample No**} & \multirow{2}{*}{ \begin{tabular}{c} **Maximal** \\ **Deviator Stress,** \\ \(q_{max}\) **(kPa)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Minimal** \\ **Deviator Stress,** \\ **(g/cm\({}^{3}\))** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Mean Deviator** \\ **Stress,** \(q_{m}\) **(kPa)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Deviator Stress** \\ **Amplitude,** \(q_{a}\) \\ **(kPa)** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **Effective Confining** \\ **Pressure,** \(\sigma^{{}^{\prime}}\!_{3,0}\) **(kPa)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Cyclic** \\ **Stress Ratio,** \\ **CSR (-)** \\ \end{tabular}  } \\  & & & & \\ \hline
1.1 & 29.3 & 23.7 & 26.5 & 2.8 & 48.5 & 0.603 \\
1.2 & 29.0 & 23.7 & 26.4 & 2.6 & 47.5 & 0.610 \\
1.3 & 43.2 & 35.3 & 39.3 & 4.0 & 45.8 & 0.944 \\
1.4 & 45.7 & 37.4 & 41.5 & 4.2 & 91.1 & 0.502 \\
1.5 The isotropic consolidation phase was terminated when the pore water effluent was less than 5 mm\({}^{3}\) per five minutes. When the consolidation was finished, we performed the undrained cyclic loading. During this test, the pore water outflow from the soil sample was cut off and the pore water pressure was measured during the test. We conducted the cyclic loading in a one-way manner, which indicates that the deviator stress minimum \(q_{min}\), and maximum \(q_{max}\) value was above 0 kPa (\(q_{max}\) and \(q_{min}\) were both in the compression). The frequency \(f\) of the loading was equal to 1 Hz and the number of cycles was between 10,000 and 50,000. We performed the tests in different effective confining stress \(p^{\prime}0\) conditions detailed in Table 2.  
The static triaxial tests on the sandy silty clay revealed that the slope of the Critical State Line \(M\) is equal to 1.33. The undrained triaxial shear tests showed that the stress path is greatly influenced by effective confining pressure.