The strength, deformation, and hydraulic properties of geomaterials, which constitute embankments, vary with fine fraction content. Therefore, numerous research studies have been conducted regarding the effects of fine fraction content on the engineering properties of geomaterials. Howe ver, there have only been a few studies in which the effects of fine fraction content on the soil skeletal structure have been quantitatively evaluated and related to compaction and mechanical properties. In this study, mechanical tests were conducted on geomaterials with various fine fraction contents to evaluate their compaction and mechanical properties focusing on the soil skeletal structure and void distribution. Furthermore, an internal structural analysis of specimens using X-ray computed tomography (CT) images was conducted to interpret the results of mechanical tests. As a result, it was discovered that the uniaxial compressive strength increased with fine fraction content, and the maximum uniaxial compressive strength was observed at a low water content, not at the optimum water content. Additionally, the obtained CT images revealed that large voids, which could ser ve as weak points for maintaining strength, decreased in volume, and small voids were evenly distributed within the specimens, resulting in a more stable soil skeletal structure.

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 behaviours of soil subjected to internal erosion have been widely investigated, yet the evolution of soil fabric anisotropy during erosion and the corresponding changes in post-erosion stiffness degradation curves have never been explored. This study developed a back-pressure-controlled, bender-equipped triaxial permeameter to measure the internal erosion behaviour of soils under different stress states and its consequences on the anisotropic mechanical behaviour of eroded soil. Evolutions of fabric anisotropy during erosion were evaluated by measuring the shear wave velocity at various wave propagation and polarisation directions under the isotropic loading condition. Soil samples with and without erosion were then sheared following a path of constant mean effective stress to determine the stiffness degradation curves. Results show that the losses of fines and the rearrangement of soil particles due to erosion increased the fabric anisotropy (i.e. increased horizontal alignments of soil particles) by 10% at all confining pressures. Such increase resulted in eroded specimens that were stronger than their intact counterparts upon triaxial compression, but the opposite trend was observed upon extension. The eroded specimens had a higher volumetric threshold shear strain than the intact ones, thereby suggesting that higher strains were required to substantially change the soil structure and reduce the small-strain shear stiffness.

This study investigates the stabilization of expansive soil using basic oxygen furnace (BOF) slag, an eco-friendly steel by-product, as an alternative to conventional stabilizers like ordinary Portland cement. By evaluating varying concentrations of BOF slag and lime as an activator, the research aims to improve the soil's mechanical properties, addressing issues like low bearing capacity and high shrink-swell potential. Bentonite clay was treated with different BOF slag ratios (10%, 20%, and 30%) and activated with lime (1%, 3%, and 5%). After mixing and compaction, samples were cured and tested for unconfined compressive strength (UCS), shear wave velocity (BE), and free swell. Microscopic analyses (SEM) provided insight into structural changes post-stabilization, revealing improved properties with increased BOF and lime concentrations. Notably, stabilization with 30% BOF slag and 5% lime achieves a compressive strength of 810 kPa, meeting the minimum subgrade soil stabilization requirement (700 kPa) set by the Federal Highway Administration. This research underscores the potential of BOF slag as a sustainable and practical material for bentonite clay stabilization, offering a promising solution for enhancing soil properties while contributing to environmental sustainability through industrial by-product repurposing.

Low-strength and highly compressible excavated clayey soils are common in geotechnical engineering, which cannot serve as a bearing stratum and typically end up being disposed of in landfills. Autoclaved aerated concrete powder (AACP) is a lightweight and porous waste material, with its stockpiles rapidly accumulating worldwide. To promote sustainable development in geotechnical engineering, a type of composite admixture consisting of cement and AACP was developed to modify clayey soils in this study. The physical and mechanical properties of untreated and the composite admixture-treated soil samples were investigated via Atterberg limits, compaction, bender element, constraint compression, free swell, and unconfined compressive strength (UCS) tests. The physicochemical and microstructural observations, including soil pH, scanning electron microscopy, and mercury intrusion porosimetry analyses, were conducted to interpret the macroscopic mechanical behaviors. Test results showed that the incorporation of AACP improved the workability of clayey soils, while cement further enhanced their mechanical properties. Hydration compounds primarily filled the voids with a diameter ranging from 0.1 to 1 mu m. From the perspective of volume change behavior, 8% cement content was recommended. Shear wave velocity showed a strong correlation with the UCS, demonstrating that the bender element technique was an effective non-destructive tool for assessing the strength of compacted samples.

The maximum shear modulus (G(0(ij))) of rooted soils is crucial for assessing the deformation and liquefaction potential of vegetated infrastructures under seismic loading conditions. However, no data or theory is available to account for the anisotropy of G(0(ij)) of rooted soils. This study presents a new model that can predict G(0(ij)) anisotropy of rooted soils by incorporating the projection of the stress tensor on two independent tensors that describe soil fabric and root network. Bender element tests were conducted on bare and vegetated specimens under isotropic and anisotropic loading conditions. The presence of roots in the soil increased G(0(VH)) at all confining pressures (p '), as well as G(0(HH)) and G(0(HV)) at low p '. However, the trend was reversed at higher p ' because the roots reduced the effects of confinement on G(0(ij)) by replacing stronger soil-soil interfaces with weaker soil-root interfaces. Roots made the soil fabric and G(0(ij)) more anisotropic. The proposed model can effectively predict the observed anisotropy of G(0(ij)) under isotropic and anisotropic loading conditions. The new model also offers a new method for determining the fabric anisotropy of sand based on the anisotropy of shear modulus.

Cohesive soils in nature are created under anisotropic stress and have various stress histories. Embankments generate greater vertical loads underground. Moreover, associated excavation activities can exacerbate the extensional stress state. This study investigated the effects of induced anisotropy on the shear modulus in saturated and unsaturated cohesive soils. A triaxial testing apparatus, equipped with local small strain (LSS) measurement devices and bender elements (BEs), was used to measure the small strain shear modulus. Two series of tests were conducted: (1) LSS and BE tests used specimens normally consolidated under a constant mean effective stress of p' = 300 kPa or net mean stress p net = 300 kPa with different stress ratios to investigate the effects of anisotropic consolidation. The values of the applied stress ratios, represented as K = r ' h / r ' v for the saturated soil and K net = ( r h - u a )/( r v - u a ) for the unsaturated soil, were 0.35, 0.43, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, and 3.5. (2) BE tests used specimens consolidated under various mean effective stresses in the order of p' = 50, 100, 200, 300, 400, 500, and 600 kPa, and swollen in reverse order under K of 0.35, 0.43, 0.6, and 1.0, to elucidate p' and the effects of the overconsolidation ratio (OCR). The results demonstrated that K -consolidation under constant p' produces large differences in initial shear modulus G 0 in saturated cohesive soil, but K net produces only slight differences in unsaturated cohesive soil because of the influence of strong matric suction. Finally, G 0 was normalized successfully considering the effects of void ratio e , K , and OCR. (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 increasing use of finite element analysis in modern infrastructure design emphasizes the importance of determining soil stiffness at small strains. This is usually represented by the normalized shear modulus degradation curve, which is crucial for accurate design. In the absence of specific measurements on the local soil, engineers often rely on empirical correlations and assume comparable behavior of soils with similar intrinsic properties. However, the application of this approach leads to uncertainties, especially for unique geological formations such as the soft cohesive soils of the Ljubljana Marsh. The main objective of this study was to determine the small strain shear modulus of Ljubljana Marsh soil with a plasticity index between 11 and 35%. Isotropic and anisotropic stress conditions were investigated as part of an extensive laboratory test program that included 45 bender element and 89 resonant column tests on 20 soil samples. By emphasizing the importance of measuring soil stiffness at small strains, this study not only provides reliable data for the development of the built environment in the Ljubljana Marsh and similar areas, but also underlines its necessity.

The small strain shear modulus is an important parameter in the assessment of soil dynamics problems. Studies on the small strain shear stiffness of volcanic ash remain rare probably because globally they cover just under 1% of the land surface. However, on a regional scale, this figure may be consequential as in the case of Japan, where about one third of its total land surface is covered by andosols. In this research, we aimed at understanding the influence of confinement time, a non-negligible parameter, contingent on the soil type, which needs to be accounted for when assessing the shear modulus. Bender element tests were conducted on allophanic volcanic ash, kuroboku soil sampled from the southern island of Kyushu in Japan. The allophanic ashes present all the characteristics of a non-textbook soil, notably high natural water content, high liquid and plastic limits and high void ratios. From the micrographic images, it was observed that the soil structure consisted of different types of porous particles (allophane, imogolite, volcanic glass and so on) at different internal spatial scales. Strong electrostatic bonding between the allophane particles means that in normal conditions the soil material exist as aggregates. The consequence is that the end of the consolidation stage is reached within a few minutes. Thus, the threshold demarcating the onset of the creep stage is different compared to sedimentary materials or other clayey soils. Based on the test results, empirical equations for predicting the time-dependent behaviour of the shear modulus were proposed.

Stiffness is one of the most important characteristics of geomaterials, and at the same time one of the most difficult to evaluate. It can be described by means of various stress-strain moduli, whose values strongly depend on the strain range and on the method of determination. The aim of the article is to evaluate and compare selected stiffness parameters (Young's modulus E and shear modulus G) of an anthropogenic soil on the basis of triaxial tests. The experiments were carried out on samples consisting of loess mixed with sand. Loess is a collapsible aeolian sediment with a high calcium carbonate content and so it is a very challenging material for geotechnical applications. The addition of sand improves its properties and increases its suitability for earthworks. The specimens were compacted with normal Proctor energy at the optimal water content, which ensured repeatability of the results. Standard triaxial tests (drained and undrained) were carried out at the effective confining stresses in the range of 50 - 350 kPa. The specimens' deformation was measured by means of external and local displacement transducers. Additionally, bender elements were used to assess the initial soil stiffness. The applied research methods allowed determination of the deformation characteristics in the range from very small to large strains. The stiffness moduli were assessed using different definitions and methods. It was confirmed that the stiffness of loess is improved by its proper compaction and addition of sand, when compared to the results available in literature for natural loesses.