# Characteristics of the Damping Ratio of Undisturbed Offshore Silty Clay in Eastern Guangdong, China
## 3 Results and Analysis
### Damping Ratios of Silty Clay  
To investigate the damping characteristics of cohesive soils, we compared our experimental results with the empirical models proposed by [PERSON] and [PERSON] [28], [PERSON] [15], and [PERSON] et al. [16]. [PERSON] and [PERSON] [28], based on extensive testing, observed that the overconsolidation ratio (\(OCR\)) of clays has a limited impact on damping ratios under certain conditions. The primary controlling factors are cyclic shear strain (\(\gamma_{\text{cy}}\)) and plasticity index (\(I_{\text{p}}\)). They proposed damping ratio curves for clays with different plasticity indices, which are recommended by the DNV (2021) guidelines [29]. [PERSON] [15] developed a four-parameter damping ratio model--reference strain, curvature coefficient, small-strain damping ratio, and scaling factor--for various soil types based on extensive geotechnical testing, which is widely utilized in seismic engineering analyses. Similarly, [PERSON] et al. [16], in agreement with [PERSON] and [PERSON] [28], suggested that the \(OCR\)  
Figure 10: Stress–strain and damping curve under asymmetric cyclic loading for normally consolidated silty clay.  
has only a minor influence on the damping ratio within a certain range. They proposed an empirical damping model for cohesive soils, accounting for the plasticity index and consolidation stress, while omitting the effect of the \(OCR\) on the damping curve.  
Figures 11 and 12 compare the experimental damping ratios for overconsolidated and normally consolidated silty clay with predictions from these empirical models. The overconsolidated silty clay at a 16-17 m depth has a plasticity index (\(I_{\text{p}}\)) of 26.6%, and the normally consolidated silty clay at 17-18 m has an \(I_{\text{p}}\) of 20.9%. As shown in Figures 10 and 11, for the [PERSON] and Dobry [21] model, the damping ratios obtained from both the resonant column and cyclic direct simple shear tests are lower than those predicted by the empirical model. Similarly, applying the average effective confining pressure, plasticity index, overconsolidation ratio, equivalent number of cycles, and cyclic loading frequency from this study to [PERSON]'s empirical model [14] yields predicted damping ratio curves. Comparing these with the test data shows that for both silty clay layers (16-17 m and 17-18 m), the resonant column results (i.e., at low cyclic strain levels) generally align well with the predictions of [PERSON]'s empirical model, while the cyclic direct simple shear test results (at medium-to-high strain levels) yield lower damping ratios than the model predicts. Using the empirical clay model proposed by [PERSON] et al. [16] to predict damping in both silty clay layers (16-17 m and 17-18 m) and comparing with the test data reveals that the [PERSON] et al. [16] predictions are broadly similar to [PERSON]'s empirical model [14]. While the model accurately predicts damping ratios at low strain levels, it overestimates damping at medium-to-high strains. Overall, all three empirical damping models tend to overestimate the damping of silty clay at medium-to-high strain levels.