The Sand Compaction Pile (SCP) method is a widely utilized ground improvement technology that enhances the density of the ground by constructing sand piles through penetration and repeated withdrawal/re-driving of a casing pipe. This method is the most widely used liquefaction countermeasure method in Japan. While the improvement effect of SCP is predominantly attributed to the resultant increase in soil density, recent studies have suggested that the stress history (such as increased lateral pressure and shear history) induced during the SCP work process also contributes significantly to its effectiveness. In order to more accurately reproduce the behavior of the ground during the construction of Sand Piles, the stress history simulating the SCP work process was applied to specimens in hollow cylindrical torsional shear tests, and the effects of the stress history were observed. The specimens were initially consolidated with a lateral stress ratio of 0.5 (K0 = 0.5). Subsequently, a stress history including increased lateral stress and cyclic shear stress was applied. Finally, liquefaction resistance was assessed through cyclic loading. After applying the stress history, an increase in liquefaction resistance was observed in these specimens. This increase was larger than that of specimens subjected only to a lateral stress increase without the shear stress history. This increasing trend persisted even after the lateral stress was reduced following the application of stress history. Finally, these test results were analyzed to assess the impact of stress history on liquefaction resistance by comparing them with the relationship between relative density and the liquefaction resistance. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

The dynamic deformation characteristics of saturated sands are considerably influenced by the loading frequency (f). Nevertheless, the effect of f on the deformation behavior of saturated coral sand (CS) has not been comprehensively investigated. This study aims to investigate how frequency (0.01-4Hz) affects the shear modulus (G) and damping ratio (lambda) characteristics of CS through a series of cyclic shear tests. The experimental results demonstrate that, under consistent initial conditions, both the strain-dependent G and lambda increase as f increases. Moreover, there is a linear relationship between the maximum shear modulus (G0) and small strain damping ratio (lambda min) with ln(f). Specifically, the regularized G of CS remains unaffected by variations in f. To facilitate the prediction of G in CS at different f, we propose a prediction equation that integrates the revised Hardin's model and Davidenkov skeleton curve. Besides, a power function expression is suggested for lambda-lambda min versus G/G0 to predict lambda in CS at different f. The revised equations for G and lambda are validated using experimental data from natural sands in the literature, confirming their suitability for evaluating strain-dependent G and lambda values of natural sandy soils over a wide strain range.

Previous studies on the hollow cylinder torsional shear test (HCTST) have mainly focused on the macroscopic behavior, while the micromechanical responses in soil specimens with shaped particles have rarely been investigated. This paper develops a numerical model of the HCTST using the discrete element method (DEM). The method of bonded spheres in a hexagonal arrangement is proposed to generate flexible boundaries that can achieve real-time adjustment of the internal and external cell pressures and capture the inhomogeneous deformation in the radial direction during shearing. Representative angular particles are selected from Toyoura sand and reproduced in this model to approximate real sand particles. The model is then validated by comparing numerical and experimental results of HCTSTs on Toyoura sand with different major principal stress directions. Next, a series of HCTSTs with different combinations of major principal stress direction (a) and intermediate principal stress ratio (b) is simulated to quantitatively characterize the sand behavior under different shear conditions. The results show that the shaped particles are horizontally distributed before shearing, and the initial anisotropic packing structure further results in different stress-strain curves in cases with different a and b values. The distribution of force chains is affected by both a and b during the shear process, together with the formation of the shear bands in different patterns. The contact normal anisotropy and contact force anisotropy show different evolution patterns when either a orb varies, resulting in the differences in the non-coaxiality and other macroscopic responses. This study improves the understanding of the macroscopic response of sand from a microscopic perspective and provides valuable insights for the constitutive modeling of sand. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Understanding the characteristics of the development of excess pore water pressure during cyclic loading is important to evaluating the dynamic behavior of soils. Many researchers have proposed experimental models to estimate pore water pressure. However, existing experimental models are mainly based on experimental results obtained under isostatic and constant amplitude loading. In this study, K0-controlled cyclic loading is undertaken by simulating a horizontal stratified ground, and the development of excess pore water pressure is evaluated by measuring the accumulated shear strain; a modified accumulated shear strain is proposed based on these results. The results show that the excess pore water pressure can be predicted from the modified accumulated shear strain, regardless of soil type, initial soil pressure coefficient, initial shear stress, or the shape of input waveform.

The present study is devoted to the investigation of the dilatancy behaviour of a fine sand based on hollow cylinder tests. Medium and dense samples were tested at a constant average stress by applying torsional angles for shear strains gamma = 1, 2, 3 and 4%. Dilatancy curves along with shear wave velocity measurements to investigate the influence of the shear strain amplitude gamma(ampl) in the shear modulus degradation curve are presented and discussed. The measured stress and strain paths were used to compare the performance of four advanced constitutive models especially in describing the dilatancy behaviour of sand. From the perspective of their constitutive equations, the differences between the simulations with various material models are examined. It may be concluded that all four models allow a proper prediction of torsional shear tests as long as a proper calibration of the material parameters is secured.