# Characteristics of the Damping Ratio of Undisturbed Offshore Silty Clay in Eastern Guangdong, China
## 2 Experimental Method
### Experimental Plan
Based on the undrained shear strength obtained from the static shear test, consolidation undrained cyclic shear tests were designed and conducted. The vertical effective consolidation stress was maintained at 119 kPa throughout the tests. The cyclic stress conditions for these tests were as follows: when the normalized average shear stress (\(\tau_{\mathrm{a}}/\sigma_{\mathrm{a}}{{}^{\prime}}\)) was 0 (representing  
Figure 3: Resonant column apparatus and direct simple shear test. symmetric cyclic loading), the normalized cyclic shear stress (\(\tau_{\rm cy}/\sigma_{\rm a}{{}^{\prime}}\)) was varied at values of 0.15, 0.22, 0.26, 0.30, and 0.36. In the case of asymmetric cyclic loading (with a normalized average shear stress \(\tau_{\rm a}/\sigma_{\rm a}{{}^{\prime}}\) of 0.18), the normalized cyclic shear stress \(\tau_{\rm cy}/\sigma_{\rm a}{{}^{\prime}}\) was set to 0.15, 0.21, and 0.22 for the cyclic shear tests. For the overconsolidated silty clay sample, taken from a depth of 17-18 m (L2), the average in situ effective vertical stress was calculated to be \(\sigma_{\rm a}{{}^{\prime}}\) = 126.5 kPa. Since the soil sample had an overconsolidation ratio (\(OCR\) = 2), the SHANSEP method was applied, consolidating the soil sample to four times its original effective vertical stress, i.e., 506 kPa, to ensure that the sample reached a normally consolidated state (\(OCR\) = 1). An undrained static direct simple shear test was performed, and the stress-strain curve is shown in Figure 5. The undrained shear strength (\(s_{\rm u}{{}^{\rm DSS}}\)) of the soil layer under the consolidation \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & **Soil Layer** & \(\tau_{\rm a}\) **(kPa)** & \(\tau_{\rm cy}\) **(kPa)** & \(t_{\rm a}\)/\(s_{\rm a}{{}^{\prime}}\) & \(t_{\rm cy}\)/\(s_{\rm a}{{}^{\prime}}\) & \(s_{\rm a}{{}^{\prime}}\) **(kPa)** & \(OCR\) & \(N_{\rm tot}\) & **Test** \\ \hline  
\hline \end{tabular} Note: \(\tau_{\rm s}\) and \(\tau_{\rm cy}\) represent the average shear stress and cyclic stress amplitude, respectively; OCR is the overconsolidation ratio; \(N_{\rm tot}\) is the total number of load cycles; DSS is the static direct simple shear test; DSScy is the cyclic direct simple shear test; RCA is the resonant column test.  
\end{table} 
Table 2: Applied loads and soil properties for the different tests. Figure 5: Stress–strain curve from static direct simple shear tests on silty clay. stress was found to be 140 kPa. Based on the results of the static direct simple shear test, undrained cyclic direct simple shear tests were designed and conducted. The vertical effective consolidation stress was maintained at 506 kPa. The tests were conducted under symmetric cyclic conditions (with normalized average shear stress \(\tau_{a}/\sigma_{a}{}^{\prime}=0\)) Normalized cyclic shear stresses (\(\tau_{cy}/\sigma_{a}{}^{\prime}\)) of 0.14, 0.17, 0.19, 0.22, and 0.25 were used. To determine the damping ratio of silty clay at low strains, GDS resonant column tests were conducted. The resonant column tests employed isotropic consolidation, with the consolidation stress set to the effective consolidation mean stress, which corresponds to the cyclic direct simple shear tests. The coefficient of earth pressure at rest (\(K0\)) for the silty clay layer was estimated to be 0.6, resulting in a consolidation confining pressure of 87.3 kPa for the 16-17 m deep silty clay layer and 371.1 kPa for the 17-18 m deep layer in the resonant column tests. We would like to clarify that the k0 coefficient for this soil layer was obtained based on CPTu data analysis and has been calibrated through indoor triaxial tests.