Hongyi Zhao’s research while affiliated with Qingdao University of Technology and other places

Calcareous sand with fines content was often encountered in offshore and onshore engineering. However, most previous research has primarily focused on the mechanical properties of clean calcareous sand. This study conducted a series of drained and undrained triaxial tests on calcareous sand-clay binary mixtures to investigate the impact of fines content on the strength and deformation characteristics of calcareous sand. The results indicate that specimens with varying fines content exhibit both strain hardening and softening behaviors under different confining pressures. With the addition of fines content from 0% to 10%, the extent of dilatancy decreases, resulting in a smaller peak friction angle compared to clean sand specimens. However, when fines content increases further to 25%, both the maximum dilatancy angle and peak friction angle show an increase. A similar trend is observed for the friction angle at the phase transition state (PTS). In the p′ − q plane, the critical state line (CSL) remains constant despite changes in fines content, whereas in the e − p′⁰.⁷ plane, the CSL shifts with variations in fines content. A unified CSL in the e − p′⁰.⁷ plane can be obtained by applying the concept of equivalent skeleton void ratio. Additionally, the state dependence of the material is analyzed using both the modified state parameter and the state index. It was observed that the friction angles at both the PTS and the peak state (PS) are influenced by the state of the material, with the PTS friction angle showing a stronger correlation with the state index, while the PS friction angle is more closely linked to the state parameter.

Submarine pipelines are the main transport carriers of marine resources. In order to protect these pipelines, geotextile and stone covering measures are adopted in this paper and the protective effect is studied. A sequence of physical model tests was conducted to carry out the research. The hydrodynamic characteristics and seabed oscillation response of the seabed surrounding the pipeline were analyzed with or without geotextile and stone cover protection, and it was found that they were affected by waves (and currents). The experimental results show the following: (1) comparing the regular wave and current with the regular wave alone, it is found that forward current promotes wave propagation and reverse current inhibits wave propagation; (2) the protective effect of geotextile and stone covering measures on different positions of the pipeline (the front, the bottom, and the back of the pipe) is basically same; (3) in the case of waves with large wave heights and long wave periods superimposed with ocean currents, the protective effect of geotextile and stone coverings on the hydrodynamic and seabed pore pressure around the pipeline is more significant.

The phenomenon of extensive erosion of silty submarine slopes in the Yellow River delta has been well documented in numerous studies. Due to poor drainage and high compressibility, silty sediments are particularly prone to pore pressure buildup and accumulated seepage under wave and current action, which can influence sediment erodibility (e.g., the critical bed shear stress and the erosion rate under various bed shear stresses). To date, there remains a lack of parametric formulation to quantitatively characterize the erodibility of silty sediments with the coupled effects of the hydraulic gradient of upward seepage and the slope gradient. In this study, a series of laboratory experiments were conducted to explore the erodibility of silt sediments from the Yellow River delta under varying hydraulic gradients of upward seepage and slope gradients. The results reveal that both upward seepage and increased slope gradients can enhance the erodibility of silty sediments. Specifically, as the seepage gradient increases from 0.1 to 0.8, the critical Shields parameter required for initiating silty particle motion decreases linearly, with a reduction rate of 0.01 per 0.1 increase in the seepage gradient, independently of changes in slope gradient. Additionally, the erosion coefficient of silty sediments grows exponentially with rising seepage gradients, with its average growth rate accelerating with increasing slope inclination. For flat sediment beds, the erosion coefficient influenced by upward seepage can be up to five times that in the absence of seepage. An empirical formula for calculating the critical Shields parameter and an erosion model incorporating upward seepage gradient and slope effects were developed through multiple regression analysis, providing an experimental basis for numerical simulations of scour in silty submarine slopes under combined waves and currents.

The utilization of geomembrane reinforcement technology is pervasive in marine sand foundation reinforcement projects. However, the elevated temperatures and intricate stress conditions prevalent in marine environments exert a notable influence on the mechanical characteristics of geomembrane interfaces comprising marine sand, which impedes the efficacy of geomembrane reinforcement in marine sand foundations. Nevertheless, there is a lack of research investigating the temperature-dependent interfacial mechanical performance of geomembranes and marine sand under diverse stress states. In this study, a series of monotonic shear tests were carried out on the interface between geomembranes and marine sand within a temperature range of 5 °C to 80 °C. These experiments were carried out using a self-developed large-scale temperature-controlled interfacial dynamic and static shear device. The experimental results demonstrate that temperature has a pronounced effect on the monotonic mechanical characteristics of the geomembrane–marine sand interface, which displays clear temperature dependence. The findings of this study may help in the design and optimization of offshore projects where a marine sand–polymer layer interface exists.

The evaluation of the wave-induced pore pressures around the offshore piles has attracted great attentions among coastal engineers, because they have been commonly used as foundations of numerous marine infrastructures. This paper presents comparative studies of the random wave-induced transient seabed response around single and double piles in a sandy seabed through a series of wave flume experiments. The influences of relative spacing ratios, wave incidence angles, and front pile diameters under different random wave parameters on oscillatory pore pressures in the vicinity of double piles are examined. In addition, variations in wave profiles and dynamic wave pressures surrounding single and double piles are quantitatively analyzed. Based on the experimental results, the following conclusions can be drawn: (1) under the influence of random waves, the wave profiles around the double piles exhibit obvious irregularity and nonlinearity; (2) the shielding effect existing in the tandem piles results in lower dynamic wave pressures around the rear pile compared to the front pile; (3) the pore pressures on the front surface of the double piles decrease with increasing soil depth, with a decreasing attenuation rate at each layer; (4) when the relative spacing ratio G/D2=3, the group-pile effect weakens, leading to an increase in the pore pressures around the rear pile, approaching the results of a single pile under conditions of lower significant wave heights or periods; (5) the intense disturbance effect caused by large wave incidence angles exacerbates the pore pressure response around the double piles; (6) when the diameter of the front pile in the tandem piles increases, it enhances the shielding effect, thus suppressing the seabed response around the rear pile. In contrast, it causes an increase in the wave surface around the double piles, exacerbating the pore pressure response in the seabed. The latter effect becomes more pronounced when the significant wave height is larger.

The sustainable development of marine environments requires a deep understanding of their chemical and biological conditions. These are significantly impacted by the exchange of substances such as contaminants, heavy metals, and nutrients between marine sediments and the water column. Although the existing literature has addressed the physics of enhanced solute migration in sediment due to sea waves, the role of coupled flow and soil deformation has often been neglected. This study investigates the effects of wave-induced soil deformation on solute release from the marine sediment using a coupled numerical model that incorporates the effect of soil deformation into the advection–diffusion equation. The results reveal that solute release is notably accelerated in deformable sediments with a smaller shear modulus, with the longitudinal dispersion coefficient increasing up to five times as the shear modulus decreases from 10⁸ Pa to 10⁶ Pa. This enhancement is more pronounced in shallow sediments as the sediment permeability decreases, where the longitudinal dispersion coefficient in deformable sediments can be 15 times higher than that in non-deformable sediments at a hydraulic conductivity of 1 × 10⁻⁵ m/s. Furthermore, the rate of solute release increases with decreasing sediment saturation due to the compressibility of pore water, although this rate of increase gradually diminishes.

This study employs a two-dimensional numerical model, coupling Biot’s poro-elastic theory with advection-dispersion equations, to examine the impact of wave nonlinearity on solute transport in deformable seabed sediment. The simulations reveal that compared to the second-order Stokes waves, the first-order cnoidal waves exhibit significant nonlinear effects, effectively enhancing the longitudinal dispersion coefficient and solute transport rate in marine sediment. However, this enhancement diminishes as wave height increases and water depth decreases, highlighting the diminishing impact of cnoidal wave nonlinearity under such conditions.

Suction anchors play a crucial role as marine supporting infrastructure within mooring systems. In engineering practice, the composite load comprising nonlinear waves and cyclic pull-out loads can have adverse effects on the seabed soil, posing a threat to the pull-out bearing capacity of the suction anchor. While existing research predominantly focuses on cyclic pull-out loads, the influence of nonlinear wave actions at the seabed surface remains overlooked. This study employs a two-dimensional integrated numerical model to investigate the dynamic soil response around a suction anchor under the influence of both nonlinear waves and cyclic pull-out loads, focusing on the mechanisms that lead to liquefaction and the deterioration of the interfacial friction due to the excess pore pressure buildup. The numerical results reveal that the cyclic pull-out load is the primary factor in the deterioration of the frictional resistance at the suction–soil interface, especially when the pull-out load is inclined with the suction anchor. Parametric studies indicate that the relative difference in frictional resistance deterioration between cases considering and excluding surface water waves becomes more pronounced in soils characterized by a small consolidation coefficient (Cv) and relative density (Dr).