The dynamic deformation characteristics of saturated sands are considerably influenced by the loading frequency (f). Nevertheless, the effect of f on the deformation behavior of saturated coral sand (CS) has not been comprehensively investigated. This study aims to investigate how frequency (0.01-4Hz) affects the shear modulus (G) and damping ratio (lambda) characteristics of CS through a series of cyclic shear tests. The experimental results demonstrate that, under consistent initial conditions, both the strain-dependent G and lambda increase as f increases. Moreover, there is a linear relationship between the maximum shear modulus (G0) and small strain damping ratio (lambda min) with ln(f). Specifically, the regularized G of CS remains unaffected by variations in f. To facilitate the prediction of G in CS at different f, we propose a prediction equation that integrates the revised Hardin's model and Davidenkov skeleton curve. Besides, a power function expression is suggested for lambda-lambda min versus G/G0 to predict lambda in CS at different f. The revised equations for G and lambda are validated using experimental data from natural sands in the literature, confirming their suitability for evaluating strain-dependent G and lambda values of natural sandy soils over a wide strain range.

The liquefaction of coral sands caused by the accumulation of excess pore-water pressure is a major factor contributing to catastrophic events on coral reefs, and accurately estimating this excess pore-water pressure accumulation holds significant importance. High-quality laboratory test results are essential for analytical or numerical calculations. In this study, a new test method is employed to conduct a series of undrained, multistaged, stress-controlled multidirectional hollow cylinder tests on saturated coral sand under complex loading conditions. The concept of threshold strain (gamma t) and the method for determining gamma t of saturated coral sand specimens under complex loading conditions are proposed. The test results demonstrate that gamma t of saturated coral sand remains insensitive to cyclic loading conditions (including frequency, stress path, and mode) but increases with increasing relative density. The range of volumetric threshold strain, degradation threshold strain, and flow threshold for saturated coral sand under different initial states and cyclic loading conditions are 0.0183%- 0.0341%, 0.0242%-0.0454%, and 1.006%-1.614%, respectively. This research provides a novel approach for accurately determining input parameters required for resolving and implementing coupled models in numerical modeling.

To investigate the effects of cyclic loading frequency (f) and loading patterns (90 degrees jump of principal stress, JPS, and continuous rotation of principal stress, CRPS) on the stiffness characteristics of saturated marine coral sands, a series of undrained cyclic shear tests were conducted. pi-plane is introduced as the analytical plane. We propose generalized deviator strain evolution (zeta q) to quantify the evolution of global strain, and introduce generalized dynamic modulus (K) to evaluate the soil's global stiffness. K and maximum generalized dynamic modulus (K0) exhibited a strong correlation with loading direction angle (alpha sigma), maximum loading direction angle (alpha sigma max), and f. Both patterns showed an increase in K0 with increasing f. Under JPS, the K0 initially decreased and then increased as alpha sigma increased, reaching its minimum value at alpha sigma = 45 degrees. Normalizing the effect of f and alpha sigma, we establish a unified empirical formula for K0. Under CRPS, K0 continuously decreased with increasing alpha sigma max. The global level of K0 is higher under CRPS compared to JPS. Additionally, the K/K0 curve was significantly influenced by alpha sigma but remained insensitive to f. A modified generalized Davidenkov model was developed to describe the recession properties of marine coral sands over a wide strain range.

The high-temperature climate, dynamic stress loading and soil particle dimension have non-negligible influence on the interface interaction between marine coral sand and polymer layer, which determines the stability of coral sand engineering facilities installed with polymers. However, currently, the relevant research is rare. In this paper, by using the self-developed large temperature-controlled interface dynamic shear apparatus, a series of cyclic shear tests were conducted on the interfaces between polymer layer and coral sand with the particle size range of 1 mm - 2 mm (S1 coral sand) and 2 mm - 4 mm (S2 coral sand) in the temperature ranging from 5 degrees C to 80 degrees C. The experimental results indicate that, from 5 degrees C to 60 degrees C, the peak shear strength, dynamic shear stiffness and damping ratio rise, while from 60 degrees C to 80 degrees C, the decline of the mechanical parameters occurs. Also, temperature has more significant influence on the dynamic mechanical properties of S1 coral sand interfaces than that of S2 coral sand interfaces. Additionally, except for 60 degrees C, the peak shear strength, dynamic shear stiffness and damping ratio of S1 coral sand interfaces is all higher than that of S2 coral sand interfaces in other test temperature.