# Characteristics of the Damping Ratio of Undisturbed Offshore Silty Clay in Eastern Guangdong, China
## 2 Experimental Method
### Experimental Plan  
Figure 2 illustrates the approximate strain level ranges for dynamic property testing of soils. From the figure, it is evident that obtaining the damping ratio of soil across low, medium, and high strain levels using a single test method is not currently feasible. The dotted lines in the figure indicate that the accuracy of the results obtained using this particular method will decrease. This study combines resonant column tests (for strain levels \(\leq\) 0.01%) and cyclic direct simple shear tests (for strain levels \(\geq\) 0.1%) to obtain a complete damping ratio-cyclic shear strain curve, as shown in Figure 3. To investigate the damping ratio characteristics of both overconsolidated and normally consolidated silty clay, two series of tests were conducted. In the first series, the soil was consolidated to its in situ stress level, maintaining its original overconsolidation ratio (\(OCR=2\)). This series involved performing both cyclic direct simple shear and resonant column tests on the overconsolidated silty clay to assess its damping characteristics. In the second series, the SHANSEP method [25] was applied to consolidate the soil samples to four times their original vertical in situ stress, effectively eliminating the soil's stress history. This was followed by conducting cyclic direct simple shear and resonant column tests on the normally consolidated silty clay to evaluate its damping characteristics. To determine the damping ratio of silty clay at medium and high strains, a series of symmetric and asymmetric cyclic direct simple shear tests (DSScy) were conducted to simulate wave loading. The cyclic loading period was set to 10 s per cycle. Initial undrained static direct simple shear tests (DSS) were performed to provide undrained shear strength parameters for the corresponding cyclic direct simple shear tests. Both the static direct simple shear tests and the corresponding cyclic direct simple shear tests used the same consolidation stress and consolidation procedure to ensure consistent consolidation conditions. The cyclic direct simple shear tests were terminated once the cyclic shear strain (\(\gamma_{\rm cy}\)) or average shear strain (\(\gamma_{\rm a}\)) reached 15%, whichever occurred first. If the test reached 1500 cycles without meeting the termination criteria, the test was stopped; refer to Figure 4 for the schematic representation of the stress and strain components. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Soil** & **Depth** & **Natural** & **Saturated Unit** & **Plasticity** & **Sand Content** & **Silt Content** & **Clay Content** \\
**Layer No.** & **Range (m)** & **Content (\%)** & **Weight (kN/m\({}^{3}\))** & **Index (\%)** & **(0.075–2 mm) (\%)** & **(0.005–0.075 mm) (\%)** & **(<0.005 mm) (\%)** \\ \hline L1 & 16–17 & 40.5 & 17.9 & 26.6 & 4.3 & 62.7 & 33 \\ L2 & 17–18 & 38.7 & 18.1 & 20.9 & 7.4 & 72.3 & 20.3 \\ \hline \end{tabular}
\end{table} 
Table 1: Basic Physical Properties of Soil Samples. Figure 2: Approximate Strain Level Ranges for the Dynamic Property Testing of Soils. Table 2 summarizes the applied loads and soil properties for the different tests conducted in this study. The overconsolidated silty clay sample, taken from a depth of 16-17 m (L1), was found to have an average in situ effective vertical stress of \(\sigma_{\mathrm{a}}{{}^{\prime}}\) = 119 kPa. A consolidated undrained static shear test was performed on the natural sample of this overconsolidated silty clay, with the effective consolidation stress set to match the in situ effective vertical stress. The resulting stress-strain curve is shown in Figure 5, from which the undrained shear strength (\(\mathrm{s_{u}}\)\({}^{\mathrm{DSS}}\)) of the soil at this consolidation stress was determined to be 52.4 kPa. Figure 5 suggests that the behavior of layers L1 and L2 are very different. In fact, the difference results mostly from the OCR values and, especially, from the effective confining stresses used in the tests (which are not those found in situ for layer L2).