There are currently two main criteria to identify the triggering time of soil liquefaction, namely when the excess pore water pressure reaches vertical effective overburden stress or the double-amplitude axial strain reaches 5 %. However, several researchers have pointed out that the excess pore water pressure may not reach confining pressure at some certain conditions, and the cycle numbers reaching liquefaction obtained by adopting two criteria for calcareous sand specimens are inconsistent, which may lead to overestimation or underestimation of the liquefaction resistance of calcareous sand. Therefore, this study introduces a parameter with physical meaning, secant shear modulus to evaluate the liquefaction potential of soil. To do that, a series of undrained shear tests were conducted on three types of sand. Firstly, the experimental results demonstrated that the difference in cycle numbers to liquefaction obtained by the two criteria increases with the increase of relative density. In addition, the study found that the degradation law of secant shear modulus with the number of cycles is not affected by loading conditions, initial state of soil, and soil type. On this basis, based on the relationship between secant shear modulus gradient and pore pressure ratio, it is highlighted that the liquefaction process can be quantitatively divided into three stages and the moment of liquefaction triggering can be correctly identified. Finally, the proposed liquefaction criterion is compared with widely used traditional criteria and latest apparent viscosity-based criterion, and the results showed that the liquefaction resistance obtained by the proposed criterion was more conservative, which benefits for reducing the occurrence of large strain development.

Calcareous sands provide the foundational support for various marine infrastructures. In the harsh marine environment, earthquake or wave loads apply multidirectional cyclic shear stresses to the foundation soil. To explore the undrained multidirectional cyclic response of sand, a series of simple shear tests were performed on reconstituted sand specimens considering the effect of phase difference (theta). By comparing the results with those of siliceous sand under similar conditions, the behavior of calcareous sand under multidirectional cyclic loading became clear. The results demonstrated that calcareous sand shows a lower degree of cyclic instability compared to siliceous sand, corresponding to the weaker strain-softening observed in calcareous sand during monotonic shear tests. The trend in normalized pore water pressure evolution in siliceous sand exceeds that in calcareous sand. Furthermore, under multidirectional cyclic shear conditions, the liquefaction resistance decreases by 30 % in extreme cases, irrespective of sand type. The liquefaction resistance of calcareous sand surpasses that of siliceous sand. However, as the cyclic stress ratio decreases, the reverse trend is observed, regardless of the impact of theta. Subsequently, the possible causes of the above experimental phenomena are explored from the perspectives of shear modulus and energy dissipation.

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.

This paper presents a comprehensive study on the evolution of the small-strain shear modulus (G) of granular materials during hydrostatic compression, conventional triaxial, reduced triaxial, and p-constant triaxial tests using 3D discrete element method. Results from the hydrostatic compression tests indicate that G can be precisely estimated using Hardin's equation and that a linear correlation exists between a stress-normalized G and a function of mechanical coordination number and void ratio. During the triaxial tests, the specimen fabric, which refers to the contact network within the particle assembly, remains almost unchanged within a threshold range of stress ratio (SR). The disparity between measured G and predicted G, as per empirical equations, is less than 10% within this range. However, once this threshold range is exceeded, G experiences a significant SR effect, primarily due to considerable adjustments in the specimen's fabric. The study concludes that fabric information becomes crucial for accurate G prediction when SR threshold is exceeded. A stiffness-stress-fabric relationship spanning a wide range of SR is put forward by incorporating the influences of redistribution of contact forces, effective connectivity of fabric, and fabric anisotropy into the empirical equation.

This study aims to evaluate the impacts of initial stress anisotropy on the variation of elastic shear stiffness of silica sand through the application of continuous shear wave velocity measurements during two distinct compression and extension loading paths. Besides, the validation of existing empirical models during both the consolidation and shearing stages is assessed. The specimens were prepared using the water sedimentation (WS) method and then consolidated with different stress ratios (eta=q/p ') from -0.6 to +0.6. Afterward, they were subjected to strain-controlled axial compression and axial extension shear in the drained condition. The shear wave velocities in the triaxial specimen were measured continuously during the consolidation and shearing stages by employing an automated small strain system. The results indicate the significant impacts of the initial stress anisotropy on the small strain shear stiffness of sand. The study also revealed that while the existing empirical correlations can be suitably applied within the elastic zone, the precision of these models in predicting the shear modulus during the shear loading when the soil's behavior enters the plastic zone is not reliable.

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.

In this study, a series of resonant column tests was conducted to measure the shear modulus of sand-rubber mixtures at small strain amplitudes (i.e. between 10(-4)% and 10(-2)%), considering different rubber percentages and confining stress levels. The results were then combined with data obtained by dynamic hollow cylinder tests to investigate shear modulus degradation of the mixtures over a wider shear strain range. Based on the test results, a new expression was proposed to improve the prediction of maximum shear modulus of sand-rubber mixtures using the modified equivalent void ratio concept. A new constitutive model was also developed for estimation of strain-dependent shear modulus of the mixtures based on the modified hyperbolic framework. The shear modulus of the mixtures was found to be a function of rubber percentage, confining stress, the modified equivalent void ratio and the relative shear stiffness of rubber and sand. The experimental data and the developed models showed that the shear modulus decreased with rubber percentage and increased with confining stress. Moreover, the reference shear strain of the modified hyperbolic model increased with both rubber percentage and confining stress while its curvature coefficient increased more considerably with rubber percentage compared to the confining stress.

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.

This study evaluated lime-lignin composite stabilisers for clay enhancement. Results showed their synergistic effect significantly improved shear strength (S), cohesion (c), friction angle (phi), and maximum dynamic shear modulus (Gmax) of clay. Microstructural analysis revealed lime-induced granular crystals and lignin-generated cementitious products, enhancing soil structure. After 1 and 7 days curing, the clay stabilised with 6% lime and 2% lignin exhibited the highest S, c, phi and Gmax. After 14 days curing, the clay stabilised with 4% lime and 4% lignin exhibited the highest S, c, phi, and Gmax. A novel relative structural characterization method based on c and phi was proposed, alongside a modified Hardin's model integrating relative structural to predict Gmax. The study demonstrates that 6% lime + 2% lignin and 4% lime + 4% lignin ratios effectively enhance embankment clay properties, offering sustainable solutions for industrial byproduct utilization and soil stabilisation in geotechnical engineering.