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.

The hypoplastic theory has gained significant attraction in the geomechanics community for constitutive modeling and numerical simulation. However, the absence of an analytical benchmark for numerical simulations incorporating the hypoplastic model remains a notable gap. This study revisits the basic hypoplastic model for normally consolidated soil, as proposed by Wu et al., by providing explicit formulations of the failure criterion and material parameters. Furthermore, closed-form hypoplastic solutions are derived for normally consolidated soil in three elemental tests: oedometer, simple shear and true triaxial tests. The solutions are assessed by comparing the analytical results with numerical integration and geotechnical test data. Additionally, a novel formula for estimating the at-rest earth pressure coefficient is derived, and compared to the widely adopted Jaky equation. Our solutions not only provide insights into hypoplastic model enhancement but also serve as robust benchmarks for numerical implementations.

As temporary support in geotechnical and tunneling scenarios, frozen soil bodies are often subjected to varying stress states during different construction stages and techniques and, thus, exhibit stepwise loading and unloading, leading to multi-stage creep. However, experimental and numerical investigations on frozen soil creep behavior have focused primarily on monotonic loading, i.e., single-stage creep. This study expands an existing experimental database on stepwise loaded creep and introduces a unique test series focusing on the uniaxial creep behavior of frozen sand under stepwise unloading and load-unload cycles. Here, similar to stepwise loaded creep, the minimum creep rate is found to remain mostly independent of the loading history, while the corresponding frozen soil lifetime depends on the latter. In contrast to equivalent single-stage creep scenarios, the lifetime becomes longer for stepwise loaded creep and shorter for stepwise unloaded creep. To consider multi-stage creep in the geotechnical design of frozen soil bodies, based on our experimental database and literature data, we test the ability of two versions of an advanced constitutive model to capture the frozen soil creep behavior under varying stress states. Comparison of the extended version, called EVPFROZEN, with the original highlights the advantages of EVPFROZEN in consistently capturing the creep rate evolution and the practically important frozen soil lifetime under complex loading histories. Combining the insights from the novel experimental database with testing and validation of the advanced constitutive model EVPFROZEN advances the efficient and sustainable design of frozen soil bodies in geotechnical applications under multi-stage loading conditions.

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.

The significance of ground freezing is becoming ever more germane as the design of new urban tunneling systems requires more complex geometries and higher bearing capacities, which are limited with conventional construction methods. Ground freezing is an advanced construction technique to make the water-saturated subsoil impermeable and temporarily increase its strength and stiffness. This study reports experimental investigations consisting of single-stage and multi-stage creep tests under uniaxial loading. The comparison of the different loading types reveals the influence of the stress-strain history on the rate- and temperature-dependent behavior of frozen granular soils. We extend the constitutive model for frozen soils proposed by Cudmani et al. (2022, Geotechnique, doi:10.1680/jgeot.21.00012) to consider stepwise loading and creep by coupling creep time with stress-strain history. Moreover, we simulate element tests and compare the simulations with our own experimental data as well as data from the literature to achieve the first step in validating the extended model. The good agreement of the numerical and experimental results confirms the constitutive model's ability to capture the main features of the complex mechanical behavior of frozen granular soils for single-stage as well as multi-stage loading under constant temperatures.