This study examines the cyclic behavior of calcareous sand obtained from the South China Sea. A series of undrained cyclic triaxial tests were performed on the calcareous sand with various relative densities, cyclic stress ratios, and effective confining pressures. The test results show that whereas the effective confining pressure exhibited a small influence on the cyclic behavior of the calcareous sand, the effect of changes in CSR and relative density was notable. Due to its angular nature, the liquefaction resistance of calcareous sand was much higher than that of silica sand. In addition, differences between calcareous and silica sands in terms of pore pressure generation characteristics and deformation responses were also observed.

Calcareous sand deposits are widespread along the shoreline in tropical and subtropical regions. Microbially induced calcite precipitation (MICP) treatment is a new method for improving the soil’s stiffness and strength. The small-strain shear modulus and damping ratio of MICP-treated calcareous sand, two critical parameters for predicting the dynamic behavior of soil, are little known. This study conducts a series of resonant column tests to investigate the dynamic characteristics of MICP-treated calcareous sand, emphasizing the influence of treatment duration and confining stress on the stiffness and damping characteristics. It analyzes the relationship between the initial dynamic shear modulus and unconfined compressive strength. In addition, empirical relationships between the reference shear strain and treatment duration or confining stress are provided. The results show that the normalized shear modulus G/G₀ of MICP-cemented calcareous sand has a higher strain sensitivity than that of untreated sand, and the Hardin–Drnevich model can describe its attenuation pattern. The effective confining stress σ_c affects the degradation characteristics of the dynamic shear modulus of MICP-treated calcareous sand with a low cementation level; however, its impact decreases as the treatment duration increases. There is a linear relationship between the reference shear strain and confining stress. While the relationship between the reference shear stain and treatment duration is a power law.

Marine clay has been attracting in-depth research on its mechanical behavior and internal structure evolution, which are crucial to marine infrastructure safety. In the formation process of marine clay, including the sedimentation and consolidation stages, the compression behavior and internal structure evolution are highly dependent on the pore water salinity. Discrete element method (DEM) simulation is a powerful tool to study the microscopic mechanics behind the complicated macroscopic mechanical behavior of marine clay. In this study, a DEM simulation scheme is systematically proposed to numerically study the macroscopic beahvior and microscopic structure evolution of marine clay in one-dimensional compression that mimics the marine clay formation process. First, the proposed calculation scheme for double layer repulsive interaction and van der Waals interaction is introduced. Then, the developed DEM simulation scheme is validated by satisfactorily reproducing the experimentally observed one-dimensional compression curves and internal structure transition from an edge-to-edge/edge-to-face flocculated structure to a face-to-face dispersed structure. Finally, evolutions of coordinate number and fabric anisotropy are quantitatively evaluated in the microscopic view. The noticeable effects of ion concentration on the internal structure evlotion and mechanical behavior of marine clay have been examined and discussed.

Wave is a common environmental load that often causes serious damages to offshore structures. In addition, the stability for the submarine artificial slope is also affected by the wave loading. Although the landslide of submarine slopes induced by the waves received wide attention, the research on the influence of solitary wave is rare. In this study, a 2-D integrated numerical model was developed to investigate the stability of the foundation trench under the solitary wave loading. The Reynolds-averaged Stokes (RANS) equations were used to simulate the propagation of a solitary wave, while the current was realized by setting boundary inlet/outlet velocity. The pore pressure induced by the solitary wave was calculated by Darcy’s law, and the seabed was characterized by Mohr–Coulomb constitutive model. Firstly, the wave model was validated through the comparison between analytical solution and experimental data. The initial consolidation state of slope under hydrostatic pressure was achieved as the initial state. Then, the factor of stability (FOS) for the slope corresponding to different distances between wave crest and slope top was calculated with the strength reduction method. The minimum of FOS was defined as the stability index for the slope with specific slope ratio during the process of dynamic wave loading. The parametric study was conducted to examine the effects of soil strength parameters, slope ratio, and current direction. At last, the influence of upper slope ratio in a two-stage slope was also discussed.

Calcareous sand deposits are widely distributed along the shoreline in ropical and subtropical regions. Microbially induced calcite precipitation treatment (MICP) is a relatively new method to improve the stiffness and strength of the soil. Little is known about the small-strain shear modulus and damping ratio of MICP-treated calcareous sand, which are two crucial parameters for the prediction of the dynamic behavior of soil. A series of resonant column tests are performed to investigate the dynamic performance of MICP-treated calcareous sand, with special attention paid to the influence of treatment duration and confining stress on the stiffness and damping characteristics. The relationship between the initial dynamic shear modulus and unconfined compressive strength is analyzed. Additionally, the empirical equations of the reference shear strain between treatment duration and confining stress are given. The G/G0 of MICP-cemented calcareous sand presents a higher strain sensitivity than that of untreated sand, and its attenuation pattern can be described by Hardin-Drnevich model. The σc has an apparent effect on the degradation characteristics of the dynamic shear modulus of MICP-treated calcareous sand with a low cementation level, however, its effect decreases with the increasing treatment duration. The relationship between the reference shear strain and the treatment duration and confining stress can be described by a power and a linear formula, respectively.

One of the challenges to the analysis of interactions between soil and piles in lateral spreading is the modeling of the progress generated by excess pore pressure and soil strength and stiffness degradation. In this paper, a pile–soil interaction analysis method that introduces the thixotropic-induced excess pore pressure model (TEPP) to describe the progressive development of the stress–strain rate connection of liquefying soil is proposed. The reliability of the method was verified by comparing the calculated results with that of the shake table test. Then, the parametric analyses of soil–pile interactions were carried out. The results show that the bending moment and horizontal displacement of pile foundations increase with the increase in superficial viscosity and inclination angle of the site. The horizontal dislocation and bending moment of the pile foundation increase with the decrease in loading frequency as a result of the property of amplifying low-frequency loads and filtering high-frequency loads of liquefied soil.