Earthquake-induced soil liquefaction causes ground and foundation failures, and it challenges the scientific community to explore the liquefaction problem in deep deposit under strong shaking. Due to the capacity limitation of physical modelling facility, it is difficult to reproduce soil liquefaction response of deep sand ground by centrifuge shaking table test. To address this problem, a suite of centrifuge model tests were conducted with the aid of Iai's Type III generalized scaling law (i.e., GSL) to observe the liquefaction response of deep sand ground, where Models 1 and 2 were used to validate the GSL and Model 3 with the validated GSL stands for the deep sand ground with prototype depth of 80 m. The test results of Models 1 and 2 indicate that GSL generally performs well for small-strain shear modulus, nonlinear dynamic response of acceleration and the generation of excess pore water pressure, but leaves considerable errors for post-shaking dissipation process and ground settlement with large plastic strain. The test results of Model 3 indicate that liquefaction is also possible in depth of 30-40 m under shaking event of PBA = 0.4 g and Mw = 7.5. For deeper depth without triggering of liquefaction, a depthdependent power function relationship between the peak excess pore water pressure and Arias intensity has been established. The test results also revealed that consolidation and earthquake shaking history contribute to the development of soil anisotropy in a deep ground, leading to a continuous increase of anisotropy degree, which could be evaluated using the small-strain shear moduli in different stress planes under orthogonal stress conditions.

In Australia, most rail systems are constructed along the coastal line, traversing soft soil deposits that can cause a series of track instabilities, including excessive plastic deformation and mud pumping. For this reason, the subgrade is considered one of the most critical components of the railway infrastructure, and the accurate prediction of its undrained shear behaviour is of utmost importance to ensure track integrity and safety over time. The subgrade is composed of naturally deposited soil, which may be modified using compaction or consolidation techniques to improve its bearing capacity. In each method, the soil presents a unique arrangement of particles, groups of particles, and voids (referred to as fabric), which govern the response of subgrade soils to the substantial loads imposed by moving trains. For this study, samples of clayey subgrade soil were collected from a site where track degradation had been reported. The soil was reconstituted using slurry consolidation and compaction methods to create different fabrics. A series of undrained cyclic triaxial tests were then carried out to investigate the influence of specimen preparation methods on the shear behaviour of soil. Differences in soil fabric were assessed through X-ray microcomputer-tomography (micro-CT), providing insights into the variations observed in the cyclic response. Based on the findings, it is evident that fabric plays a crucial role in the shear behaviour of subgrade soils and should, therefore, be considered in railway infrastructure design.

The soils in situ are subjected to various types of preloading histories. Extensive work has been devoted to understanding the impact of undrained preloading with different strain histories on the reliquefaction resistance of sands. This study primarily examines the effects of drained cyclic preloading histories on the liquefaction resistance of soils using DEM-clump modeling. The effects of preloading stress path and preloading deviatoric stress amplitude on the drained cyclic behavior and subsequent undrained liquefaction response are discussed. Moreover, the evolution of two microscale descriptors, including coordination number Z and fabric anisotropy degree ac, during the total process is analyzed. The results demonstrate that a smaller preloading stress amplitude and an increasing preloading cycle generally increase the liquefaction resistance of sandy soils. In comparison, a larger preloading stress amplitude significantly reduces the liquefaction resistance. We also reveal that drained cyclic preloading histories induce soil samples with different relative densities and fabrics. The relationship between relative density and liquefaction resistance of soils is not unique. Essentially, Z and ac are good indexes for determining the liquefaction resistance of soils with various drained cyclic preloading histories. The primary objective of this study is to elucidate the micromechanical effects of drained cyclic preloading on the liquefaction resistance of sandy soils.

While the fabric of soil can significantly influence its behaviour, the effect of varying fabric parameters on the subgrade shear response is still not well understood. This study creates soil specimens with different fabrics which are then captured through X-ray microscopic-computed tomography scanning and quantified by image processing techniques. A comprehensive laboratory investigation is conducted to understand how the soil fabric affects its monotonic and cyclic shear behaviour. The results indicate that the consolidation method creates a more homogeneous fabric with mainly small-to-medium interconnected pores, whereas the compaction technique creates significantly large and mostly inter-aggregate pores with lower connectivity. In this regard, the consolidated specimens exhibit an elastic-perfectly plastic behaviour, while the compacted specimens show strain-hardening transformation during isotropic monotonic shearing. Under anisotropic conditions, the compacted specimens exhibit a greater strain softening response and excess pore pressure than the consolidated specimens because they have a weaker fabric. Furthermore, the compacted specimens show a smaller threshold strain at a lower critical number of cycles due to the collapse of large pores. These current findings prove the decisive role that soil fabric plays in determining the shear response and failure of subgrade soils.

This contribution investigates the characteristics of elastic wave velocities (Vp and Vs) during triaxial shearing tests under dry and drained conditions. Samples of tested materials with different particle morphologies (i.e., particle shape and surface roughness) were prepared under three strategies, namely, similar initial void ratios (e0), relative densities (Dr0), and side tapping numbers (Nt). Regarding the elastic wave velocities as functions of e0 and confinement r at very small strain ranges, i.e., V = a(B - e0)(r 1kPa)b, a was seen to increase for more angular materials or smoother surfaces, while b and B were seen to decrease as the particles became more angular or the surfaces became smoother. During triaxial shearing, Vp increased initially and then tended to decrease more gently, whereas Vs increased initially and then showed a marked decrease before convergence upon shearing regardless of the e0 for the given material. The influence of particle morphology on the absolute values for Vp and Vs was found to be complex during shearing, whereas the wave ratio (Vp/Vs) was consistently greater under rougher conditions for the same shape. Importantly, the wave ratio (Vp/Vs) was found to correlate well with the particle morphology: more angular materials and rougher surfaces exhibited a greater Vp/Vs ratio normalized by the stress and density conditions for each material, which further indicates a higher degree of fabric anisotropy with reference to the microscopic evidence in the literature. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The volumetric deformation of clayey soils, leading to a reduction in the bearing capacity and serviceability of pavements and building structures, is a major concern during their design, construction, and maintenance. Several approaches are often followed to mitigate the volume expansion and concomitant damage, including removal and replacement, moisture treatment with appropriate compaction protocols, and chemical treatment. During these treatment processes, the in-situ fabric is altered as the natural undisturbed soils are remolded and compacted. Hence, it is crucial to understand the effect of remolding on the volumetric characteristics of clayey soils. To investigate this effect, coefficient of linear extensibility (COLE) tests were conducted on both natural and remolded soil samples. The objective was to evaluate the impact of soil fabric modification on volumetric characteristics such as suction compressibility index (gamma h) and soil water-retention characteristics, i.e., the soil-water characteristic curve (SWCC) of clayey soils. Our findings indicated that remolded soils had approxi-mately 10% to 30 % higher gamma h-values than those of unaltered soils, which can be attributed to changes in porosity. Two distinct mechanistic models were developed using the packing theory concept to link the gamma h-value and SWCC of remolded and natural soils. Finally, an analysis was conducted to compare the potential vertical movement (PVM) of natural and remolded clay soils. This analysis revealed that the remolded soil fabric sub-stantially increased the PVM values, particularly for high-plasticity clay soils. This effect should be considered when assessing the impact of treatment that requires remolding, which substantially alters the soil structure and fabric.

Pore water pressure (PWP) build-up essentially takes place in loose, water saturated, coarse-grained soils causing the reduction of effective stresses and soil stiffness (soil liquefaction). Considering the same internal structure (soil fabric), stress level, loading amplitude etc. the response of different soils to external disturbance is different. Therefore, the increase of PWP or tendency to soil liquefaction is dependent on the granulometric properties of soils. This paper reveals a simple cyclic shear test that enables the comparison of the sensitivity of PWP build-up to density changes for different sands. The presented test allows a fast installation of a soil specimen and a subsequent constant volume cyclic shearing within a short time period (ca. 30 minutes). The results successfully confirm the repeatability of the method as well as the dependence of the PWP build-up on the initial relative density and saturation degree. It is also shown that the soil fabric has an essential influence on the build-up of PWP. The method aims to allocate an index value to every tested sand and thus to quantify a sensitivity of different sands to density changes with respect to liquefaction.