Reinforced concrete (RC) sheds with sand cushions laying on the top are commonly adopted to resist rockfall impacts. To improve the rockfall-impact resistance of RC shed with sand cushion, this study investigated the buffering performance of sand cushion and examined the effect of sand cushion on the dynamic behaviors of RC shed. Firstly, a series of impact tests on sand cushion were conducted to analyze the influence of cushion thickness and falling height of rockfall on the penetration depth into the cushion, impact force and impact duration, as well as the development of vertical and horizontal stresses inside the cushion. Then, a finite elementdiscrete element coupling model was established to consider the particle interaction of sand cushion under rockfall impacts and impact behaviors of RC shed. Finally, based on the validated numerical analysis method, the effect of sand cushion on the dynamic responses and damage of prototype RC shed subjected to the impact of rockfall was simulated and evaluated. The results showed that: (i) with the increase of cushion thickness, the peak impact force was reduced, but the penetration depth and duration increased; as the falling height elevated, the impact force and penetration depth increased while the duration was shortened; (ii) sand cushion had excellent buffering performance to attenuate vertical and horizontal stresses inside the cushion; (iii) stress diffusion angle formed in the sand cushion can enlarge the load-bearing area at the bottom of the cushion, and the buffering performance of sand cushion can be improved through increasing the stress diffusion angle; (iv) compared with the non-cushion one, the rockfall-impact resistance of RC shed was effectively improved by the sand cushion through reducing impact force, penetration depth, dynamic bending moment and shear force of the shed roof, as well as transforming brittle punching-shear failure of the shed roof into flexural failure.

Previous studies investigating dynamic responses of gravelly soil were limited to high-strain conditions, in which a high level of pore-water pressure is developed, leading to a significant reduction in shear strength and subsequent liquefaction. This paper presents a series of dynamic centrifuge modeling tests performed on loose gravel-sand mixtures to evaluate progressive response under various shear strains. The centrifuge models simulated a uniform soil profile of gravel-sand mixtures with gravel contents of 20%, 40%, 65%, 80%, and 100% that were subjected to incrementally increasing shaking amplitudes from 0.01 to 0.40 g. Due to the influence of composition on the void ratio of the specimens, the results were analyzed in terms of their dominant behaviors (i.e., sandlike, gravellike, or transition soil). Although the soils had comparable initial relative densities, the sandlike soils had the lowest void ratio, and the void ratio increased when the gravel content was greater than 65%. Resonant column testing results indicated that the soils had comparable dynamic properties because of their loose condition. The results showed that dynamic shaking generates comparable shear strains ranging from 0.03% to 3.8% in all models, but the accumulation of pore pressure leads to upward flow in sandlike soils, whereas transient pore-pressure behavior leads to oscillatory flow in gravellike soils. Differences in the stress-strain response and the effects of the number of shaking cycles were observed in different soil mixtures depending upon the level of excess pore pressure. At low shaking amplitude and low excess pore pressure, stiffness degradation was observed while the stress-strain loop was symmetric. At high shaking amplitude and high excess pore pressure, significant stiffness degradation was observed followed by shear-induced dilation resulting in an asymmetrical stress-strain loop. This study clarifies the differences in the dynamic responses and behaviors of sandlike, gravellike, and transition soil over a wide range of strains.

This study examined the geotechnical behavior of silty sand soil treated with cement and cement-mineral polymer through a series of static and dynamic tests. Uniaxial Compressive Strength (UCS) and Indirect Tensile Strength (ITS) tests were conducted on specimens with varying amounts of cement and polymer (ie, 5, 7 and 9% by weight). Based on the results of UCS and ITS tests, the optimal combination of 7% cement and 7% cement-polymer was selected. Subsequently, California Bearing Ratio (CBR), Freezing and Thawing (F-T), and Large-scale cyclic triaxial (LCT) tests were performed on the optimal combinations. The results indicate that the treatment improves UCS, stiffness, CBR, and durability. By adding the polymer, the maximum UCS Sof the te cement treated specimen can be achieved in a shorter curing period. Moreover, when exposed to F-T cycles, the cement-polymer specimen exhibited. improvements in weight loss (about 0.6%) as well as compressive and tensile strength (about 200 kPa) compared to the cement treated specimen. In the dynamic tests, the cement-polymer specimen outperformed the cement specimen at low to medium cyclic deviatoric stress levels (up to 275 kPa). However, at higher stress levels, this trend was reversed. This behavior can be attributed to the formation of microcracks and cracks due to growth of needle-shaped microcrystals in cement-polymer specimen. Additionally, the cement-polymer treated specimen experienced lower permanent deformation during cycling loading Overall, the polymer additive proves to be more effective in treating the base layer that withstands low and moderate stress levels, making it a suitable complement to a portion of cement

In this study, a series of shaking table model tests were performed to evaluate the dynamic earth pressure acting on pile foundation during liquefaction. The dynamic earth pressure acting on piles were evaluated with depth and pile diameters comparing with excess pore water pressure, it means that the kinematic load effect plays a substantial role in dynamic pile behavior during liquefaction. The dynamic earth pressure acting on pile foundations with mass exhibited significant similarity to those without upper mass. Analyzing the non-fluctuating and fluctuating components of both excess pore water pressure and dynamic earth pressure revealed that the non-fluctuating component has a dominant influence. In case of non-fluctuating component, dynamic earth pressure is larger than excess porewater pressure at same depth, and the difference increased with depth and pile diameter. However, in the case of the fluctuating component, the earth pressure tended to be smaller than the excess pore water pressure as the depth increased. Based on the results of a series of studies, it can be concluded that the dynamic earth pressure acting on the pile foundation during liquefaction is applied up to 1.5 times the excess pore water pressure for the non-fluctuating component and 0.75 times the excess pore water pressure for the fluctuating component.

The increasing mean sea depths have necessitated wind turbine foundation to have larger moment resistance capacity, from early design of monopiles to recent piled jackets. Design-oriented pile-soil interaction model (API t-z model) is modified for cyclic loading with a simple correction factor, with little attention paid to stiffness degradation and displacement accumulation caused by cyclic shakedown and ratcheting. Assisted by a bounding surface plasticity-based cyclic t-z model, this study aims to investigate the influence of t-z modeling on integrated analyses of jacket offshore wind turbines through modifying the open-source OpenFAST software. Demonstrated by the NREL 5 MW offshore wind turbine supported by piled jacket, the results show that the cyclic weakening of pile-soil interface leads to an upright load transfer from the vertical interface of the pile with degraded t-z resistance, to its lateral interface by mobilizing more p-y resistance. Ignorance of the stiffness degradation and displacement accumulation would mis-estimate modal properties, cumulative deformation, loading sharing behavior and stress transfer mechanism significantly, suggesting the model's merits in deformation control and stress transfer for piled jacket in feature design.

With the increasing use of oceans for engineering purposes, such as the installation of suction anchors and pipelines, the stability of seabed structures has become a pivotal concern and is intricately linked to the characteristics of seabed soils. This study focuses specifically on deep-sea soft clay, a predominant seabed soil type distinguished by its high water content, thixotropy, and low permeability. These clays are vulnerable to destabilization and damage when disturbed, thereby posing threats to seabed installations. While the existing literature extensively examines the cyclic behavior of clay, considering factors such as the pore pressure response and strain and deformation characteristics, there is a notable gap in research addressing the behavior of deep-sea soft clay under comprehensive stress levels and prolonged cyclic loading. In this study, cyclic shear tests of the natural marine clay of the South China Sea were conducted, and the cyclic stress ratio (CSR), overpressure consolidation ratio (OCR), consolidation ratio (K c), and loading frequency were varied. It was found that the CSR, OCR, and K c significantly impact the cumulative dynamic strain in deep-sea soft clay during undrained cyclic dynamic tests. Higher CSR values lead to increased dynamic strain and structural failure risk. Subsequently, a dynamic strain-dynamic pore pressure development model was proposed. This model effectively captures the cumulative plastic deformation and dynamic pore pressure development, showing correlations with the CSR, OCR, and K c, thus providing insights into the deformation and pore pressure trends in deep-sea clay under high cyclic dynamic loading conditions. This research not only furnishes essential background information but also addresses a critical gap in understanding the behavior of deep-sea soft clay under cyclic loading, thereby enhancing the safety and stability of seabed structures.

In order to explore the dynamic behavior and damage mode of shallow buried tunnel induced by underwater explosions (UWEPs), a fully coupled numerical model of a shallow buried tunnel based on Arbitrary Lagrangian and Eulerian (ALE) method was established. The strain rate effects of concrete and steel bar under explosion load, the explosion wave propagation, the interaction between fluids and solids, and the nonlinear response of the structure were considered. The reliability of the numerical method was verified by comparing the experimental and analytical results. The damage process and damage mechanism of submerged shallow buried tunnel due to UWEPs were investigated. The effects of saturated soil covering, explosive weight, buried depth and water depth on the dynamic behavior and damage mode of the tunnel were discussed. Finally, the dimensional analysis was used to obtain the functional relationship between the peak displacement, charge weight, buried depth and water depth. The results show that the saturated soil covering can effectively reduce the impact of explosion load on the tunnel. Increasing the buried depth can mitigate the blast effects on the structure, and the failure modes switch from local damage to global failure. The response of the tunnel increases with the increasing water depth, but the influence of water depth decreases gradually. The damage modes of shallow buried tunnel can be classified into local punching or spalling damage, global bending failure accompanied by spalling damage, and global bending failure.

Extra-large liquefied natural gas (LNG) storage tanks are comprised by a steel inner tank and an outer protective tank of prestressed reinforced concrete (PRC), both being very thin. These important lifeline infrastructures are prone to damage and even failure under earthquake during their service life. Convincing numerical simulation, verified by shake table tests, is a feasible tool to quantify the seismic responses and to mitigate the potential damage/failure of LNG storage structures. This work addresses systematically the three-dimensional finite element (FE) modeling, experimental validation and numerical simulations of such structures, with the soil-pile interaction of the foundation, the fluid-structure interaction of the inner tank and damage of the outer tank all properly accounted for. For the sake of computational efficiency with no loss of too much precision, the soil-pile interaction is described by the mass-damper-spring model, and the fluid-structure interaction by the mass-spring model with both the convective and impulsive components accounted for. Moreover, the nonlinear mechanical behavior of concrete is considered by the damaged-plasticity model regularized with the fracture energy. The concrete-steel interaction in PRC is practically dealt with by modifying the constitutive relations of concrete and steel rebars/tendons properly with the equilibrium and compatibility conditions accounted for. The FE modeling strategy is validated against the recently conducted benchmark shaking table test of a scaled extra-large LNG storage structure. The capability in capturing the overall dynamic responses, e.g., the hydrodynamic pressure and structural vibrations under seismic actions, etc., is sufficiently verified. Finally, the dynamic responses and structural reliability of an extra-large LNG storage tank under deterministic and stochastic seismic actions are numerically studied in details.

Expansive soils are distributed across a wide area in China, and land transport and surface construction will inevitably involve these soils. To mitigate the deficiencies of single-method expansive soil modification, it is highly important to adopt the use of polyvinyl alcohol (PVA) to improve expansive soils and enhance the strength and toughness of modified soils. In addition, solidification technology can be utilized for the resource utilization of expansive soils. In this study, triaxial testing is employed to evaluate the mechanical properties of solidified soil. When the confining pressure is the same and with increasing PVA content, soil particles and PVA combine to form a cemented substance, which fills the internal pores of the soil samples, enhances the cohesion between soil particles, and improves the bearing capacity of the soil. The stress-strain curve for the modified soil first increases and then decreases. The shear strength peaks at a PVA content of 3%. Based on the improved soil with a 3% PVA content, GDS dynamic triaxial tests were carried out to investigate the effects of different confining pressures and frequencies on the dynamic stress-strain curves, dynamic modulus of elasticity, and variation rule for the damping ratio of the improved soil. The results show that the dynamic stress-strain curve for the improved soil increases with increasing confining pressure and frequency and that the dynamic stress-strain backbone curves exhibit significant nonlinearities at different frequencies and circumferential pressures. The dynamic elastic modulus increases with increasing confining pressure and frequency and decreases gradually with increasing dynamic strain. The initial dynamic modulus of elasticity increases with increasing envelope pressure and frequency but is less affected by frequency, and the damping ratio decreases with increasing confining pressure and frequency. Soil treatment can improve the pore distribution, inhibit the extension of soil cracks, and enhance soil compactness.