Lignin fiber is a type of green reinforcing material that can effectively enhance the physical and mechanical properties of sandy soil when mixed into it. In this study, the changes in the dynamic elastic modulus and damping ratio of lignin-fiber-reinforced sandy soil were investigated through vibratory triaxial tests at different lignin fiber content (FC), perimeter pressures and consolidation ratios. The research results showed that FC has a stronger effect on the dynamic elastic modulus and damping ratio at the same cyclic dynamic stress ratio (CSR); with the increase in FC, the dynamic elastic modulus and damping ratio increase and then decrease, showing a pattern of change of the law. Moreover, perimeter pressure has a positive effect on the dynamic elastic modulus, which can be increased by 81.22-130.60 %, while the effect on the damping ratio is slight. The increase in consolidation ratio increases the dynamic elastic modulus by 10.89-30.86 % and the damping ratio by 38.24-100.44 %. Based on the Shen Zhujiang dynamic model, a modified model considering the effect of lignin fiber content FC was established, and the modified model was experimentally verified to have a broader application scope with a maximum error of 5.36 %. This study provides a theoretical basis for the dynamic analysis and engineering applications of lignin-fiber-reinforced sandy soil.

Cemented sand-gravel (CSG) is an innovative material for dam construction with a wide range of applications. Nevertheless, a comprehensive understanding of the dynamic properties of CSG is lacking. A series of cyclic triaxial dynamic shear tests were carried out on CSG materials to investigate their complex dynamic mechanical properties, leading to the establishment of a dynamic constitutive model considering damage. The findings indicate that both the application of confining pressure and the addition of cementitious material have a noticeable influence on the morphology of the hysteresis curve. Further research scrutiny reveals that augmenting confining pressure and gel content leads to an increase in the dynamic shear modulus and a decrease in damping ratio. Furthermore, a constitutive dynamic damage constitutive model was constructed by linking a damage element to the generalized Kelvin model and defining the damage variable D based on energy interaction principles. The theoretical formulas for dynamic shear modulus and damping ratio were adjusted accordingly. In addition, the stiffness matrix of the dynamic damage constitutive model was derived, which demonstrated its strong fitting effects in dynamic triaxial shear tests on CSG. Finally, the dynamic response and damage distribution in the dam body under dynamic loading were analyzed using a selected CSG dam in China.

Damping plays a crucial role in the design of offshore wind turbine (OWT) monopile foundations. The soil damping of the monopile-soil system (MSS) represents the energy dissipation mechanism arising from the interaction between the pile and the soil. It is typically derived by back-calculating from the overall damping measured in the entire OWT structure. However, few studies have independently examined the soil damping in MSS, and the impact of key parameters such as pile diameter, pile embedded depth, cyclic load amplitude, and load eccentricity on the variation of soil damping in MSS remains unclear. This paper introduces an elastoplastic-damage constitutive model for the numerical simulation of the damping ratio variation in seabed soil and MSS. The model is implemented in ABAQUS software and validated against cyclic triaxial tests on stiff clay soil. On this basis, a three-dimensional finite element sensitivity study was conducted to elucidate the effect of these key parameters on the MSS damping ratio. The results of the study reveal that the MSS damping ratio exhibits a nonlinear and asymmetric trend as the loading cycles increase. The MSS damping ratio decreases with increasing pile diameter and embedded depth but increases with increasing lateral cyclic load amplitude and load eccentricity from the mudline.

The study includes the dynamic characterization of clayey soil blended with nano-SiO2 and fly ash under cyclic loading at high strain. The percentages of nano-SiO2 varied between (0.5-7)%, and fly ash varied between (10-30)% by weight of the soil. The optimal dosages of nano-SiO2 and fly ash were established by employing the outcome of the static test results. The cyclic triaxial (CTX) tests and bender element (BE) tests were carried out to determine the G and D of the composite material and to develop normalized modulus reduction (G/G(max)) and damping ratio curves for the same. The strain-controlled cyclic triaxial tests were conducted for a shear strain range of 0.6-3.0% at a loading frequency of 1 Hz and an adequate confining pressure of 100 kPa. The findings indicated that with the rise in cyclic shear strain (gamma), the G decreases while the damping ratio increases. The hyperbolic models were used to build the curve fitting between the G/G(max) and the damping ratio curve with various gamma. As a result, the correlations between the empirical models fit the database well. The established correlations can be suitable for predicting the seismic behavior of the nano-SiO2 and fly-ash-treated clayey soil under various strain conditions. Furthermore, the carbon footprint and cost analysis of nano-SiO2 and fly ash treated clay soil were compared with the traditional stabilizers. The use of nano-SiO2 and fly ash in stabilizing the clayey soils contributes toward sustainable development and a reduced carbon footprint.

In order to gain a more accurate understanding of the dynamic characteristics of soil, vibration triaxial tests were conducted on representative sand and clay samples from the Beijing area. The study investigated the influence of varying loading frequencies, cyclic stress ratios, and confining pressures on soil strength and liquefaction resistance, while also analyzing changes in shear modulus and damping ratio. The dynamic shear modulus of both sand and clay decreases with increasing shear strain, with higher confining pressures resulting in larger shear moduli. For sand, the damping ratio decreases as shear strain increases; however, for clay it initially increases before decreasing. Overall, clay exhibits a larger dynamic shear modulus but smaller damping ratio compared to sand. The number of cycles experienced by both sand and clay samples decreases with increasing confining pressure or deviational stress. As loading frequency increases, the number of cycles gradually rises for sand samples but first increases then decreases for clay samples. The damping ratio of sand gradually declines with an increase in cycle count while that of clay remains relatively stable. The variations observed in shear modulus and damping ratio are influenced by factors such as loading frequency, confining pressure, and stress.

Soil-pile interaction damping plays a crucial role in reducing wind turbine loads and fatigue damage in monopile foundations, thus aiding in the optimized design of offshore wind structures and lowering construction and installation costs. Investigating the damping properties at the element level is essential for studying monopole-soil damping. Given the widespread distribution of silty clay in China's seas, it is vital to conduct targeted studies on its damping characteristics. The damping ratio across the entire strain range is measured using a combination of resonant column and cyclic simple shear tests, with the results compared to predictions from widely used empirical models. The results indicate that the damping ratio-strain curve for silty clay remains S-shaped, with similar properties observed between overconsolidated and normally consolidated silty clay. While empirical models accurately predict the damping ratio at low strain levels, they tend to overestimate it at medium-to-high strain levels. This discrepancy should be considered when using empirical models in the absence of experimental data for engineering applications. The results in this study are significant for offshore wind earthquake engineering and structural optimization.

Prediction of the intensity of earthquake-induced motions at the ground surface attracts extensive attention from the geoscience community due to the significant threat it poses to humans and the built environment. Several factors are involved, including earthquake magnitude, epicentral distance, and local soil conditions. The local site effects, such as resonance amplification, topographic focusing, and basin-edge interactions, can significantly influence the amplitude-frequency content and duration of the incoming seismic waves. They are commonly predicted using site effect proxies or applying more sophisticated analytical and numerical models with advanced constitutive stress-strain relationships. The seismic excitation in numerical simulations consists of a set of input ground motions compatible with the seismo-tectonic settings at the studied location and the probability of exceedance of a specific level of ground shaking over a given period. These motions are applied at the base of the considered soil profiles, and their vertical propagation is simulated using linear and nonlinear approaches in time or frequency domains. This paper provides a comprehensive literature review of the major input parameters for site response analyses, evaluates the efficiency of site response proxies, and discusses the significance of accurate modeling approaches for predicting bedrock motion amplification. The important dynamic soil parameters include shear-wave velocity, shear modulus reduction, and damping ratio curves, along with the selection and scaling of earthquake ground motions, the evaluation of site effects through site response proxies, and experimental and numerical analysis, all of which are described in this article.

Coastal regions often face challenges with the degradation of cementitious foundations that have endured prolonged exposure to corrosive ions and cyclic loading induced by environmental factors, such as typhoons, vehicular traffic vibrations, and the impact of waves. To address these issues, this study focused on incorporating Nano-magnesium oxide (Nano-MgO) into cemented soils to investigate its potential impact on the strength, durability, corrosion resistance, and corresponding microstructural evolution of cemented soils. Initially, unconfined compressive strength tests (UCS) were conducted on Nano-MgO-modified cemented soils subjected to different curing periods in freshwater and seawater environments. The findings revealed that the addition of 3% Nano-MgO effectively increased the compressive strength and corrosion resistance of the cemented soils. Subsequent dynamic cyclic loading tests demonstrated that Nano-modified cemented soils exhibited reduced energy loss (smaller hysteresis loop curve area) under cyclic loading, along with a significant improvement in the damping ratio and dynamic elastic modulus. Furthermore, employing an array of microscopic analyses, including nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), revealed that the hydration byproducts of Nano-MgO, specifically Mg(OH)2 and magnesium silicate hydrates, demonstrated effective pore space occupation and enhanced interparticle bonding. This augmentation markedly heightened the corrosion resistance and durability of the cemented soil.

Two new structure-specific scalar intensity measures for plane steel frames under far-field earthquakes are proposed. These intensity measures of the spectral acceleration and spectral displacement type are multi-modal as they take into account the effect of the first four natural periods and multi-level as they are defined for four performance levels and consider inelasticity and period elongation up to the collapse prevention level. This is accomplished with the aid of the equivalent modal damping ratios of a structure previously developed by the authors for performance-based seismic design purposes. These modal damping ratios are period, soil type and deformation dependent and associate the equivalent linear structure to the original nonlinear one. The proposed intensity measures are conceptually simple, elegant and include all the aforementioned features in a rational way without artificially combining terms, defining period ranges and adding coefficients to be determined by optimization procedures as it is the case for all the existing measures, which try to take into account more than one mode and inelasticity. Comparison of the proposed intensity measures against some of the most popular ones existing in the literature, with respect to efficiency (beta), practicality (b), proficiency (zeta), sufficiency in terms of seismic magnitude (M) and source-to-site distance (R), scaling robustness and the range of their values at any damage or performance level demonstrates their very good performance as indicators of the destructive power of an earthquake.

Shaking-table model experiments were conducted to study the dynamic response and damage mechanisms of pile-network composite high-speed railway foundations under seismic action. By inputting seismic waves of various types and acceleration amplitudes, the surface damage phenomena, acceleration response, and displacement response of the roadbed during vibration were analyzed. The time frequency information and energy distribution were examined using Hilbert marginal spectrum theory. Additionally, the damage mechanisms of the model were explored through transfer function analysis. The results indicated that the soil surface deformation measured using particle image velocimetry closely matched the observed macroscopic phenomena. The Peak Ground Acceleration amplification coefficients exhibited clear delamination before the structure showed signs of damage, indicating a significant energy-absorbing effect of the bedding. Spectral analysis revealed that as the vibration intensity increased, the nonlinear characteristics and damage effects of the model became more pronounced, and its ability to dissipate energy strengthened. Energy became more concentrated in the left half of the top of the model. Moreover, as the vibration intensity increased, the self-oscillation frequency of the roadbed decreased, the stiffness diminished, the damping ratio increased, and the seismic energy dissipation improved.