Gravelly soils, characterized by a distinctive combination of coarse gravel aggregates and fine soil matrix, are widely distributed and play a crucial role in geotechnical engineering. This study investigates the mechanical behavior of gravelly soil subjected to simulated freeze-thaw (F-T) cycles using triaxial compressive strength tests. The long-term deviatoric stress response of specimens with varying gravel content and initial water content was analyzed under three distinct effective confining pressures (100, 200, and 300 kPa) across different F-T cycles. The results indicate that compressive strength is significantly influenced by gravel content, initial water content, and confining pressure. Notably, the rate of increase in deviatoric stress does not exhibit a proportional rise under confining pressures of 200 kPa and 300 kPa after 40 F-T cycles. However, a direct correlation is observed between deviatoric stress and increasing confining pressure (100, 200, and 300 kPa) over 2-, 4-, and 6-day intervals, this effect is more pronounced at higher confining pressures. The deviatoric stress peaks at different strain thresholds depending on the applied confining pressure; furthermore, no evident strain-softening behavior is observed across the tested conditions. These findings suggests that higher confining pressure inhibits particle displacement and interlocking failure, thereby reducing both the void ratio and axial strain within the soil matrix. Overall, these insights enhance our understanding of the complex interactions among gravel content, water content, confining pressure, and freeze-thaw effects, contributing to the understanding of the compressive strength evolution in gravelly soils under cyclic environmental loading.

Freeze-thaw (F-T) cycle tests and triaxial shear tests are conducted under varying freezing ambient temperatures and different F-T cycles for remolded loess. The results indicate that nearly all stress-strain curves of remolded loess exhibit strain-hardening behavior under varying freezing ambient temperatures and different F-T cycles. A decrease in freezing temperature alters the yield strain of loess and diminishes its resistance to deformation. As the freezing temperature decreases and the number of F-T cycles increases, the failure deviatoric stress of loess initially decreases, then increases, and eventually stabilizes. The most detrimental freezing temperature is -12 degrees C, which significantly exacerbates the adverse effects of F-T cycles on failure deviatoric stress. The strength indices initially decrease and then increase with decreasing freezing temperatures, while they first decrease and then stabilize with an increasing number of F-T cycles. Notably, the deterioration of cohesion is significantly greater than that of the internal friction angle. A quantitative analysis is conducted to examine the relationship between failure deviatoric stress, shear strength index, temperature, and freeze-thaw cycles. The fitting results effectively quantify the influence of different variables on the strength characteristics of loess. The findings of this research have significant theoretical implications for practical engineering applications in the northwest loess region.

Granular soils creep and age. Previous findings on the time-dependent phenomena under deviatoric stress are summarized and extended with the results of an experimental investigation. Multi-stage triaxial compression tests with creep phases at different deviatoric loading on medium-dense and dense samples of a uniformly graded silica sand confirm an increase in stiffness after creep phases. Contact maturing, contact homogenization, and stabilization of the soil structure are known causes for ageing reported in the literature. As other results found in the literature, the volumetric creep behavior can be dilatant, contractant or of negligible strain close to zero and depends on the trend of the volumetric strain resulting from deviatoric loading at the beginning of creep. By the triaxial tests it is shown that dilatant creep results in an increase of the radial strain due to grain rearrangements. The axial strain rates during creep and changes of the small-strain shear modulus (ageing) follow a power law with time. According to the experiments, the exponent of the proposed power law describing the development of strain and shear modulus at small strain during creep is independent of the density and stress state. The small-strain shear stiffness and the associated soil structure at the onset of creep determine the subsequent ageing behavior. A linear dependency was found between the related ageing rates and axial strain rates during creep, which can be used to predict ageing of granular materials in combination with rate-dependent constitutive models.

The premature failure or early deterioration of mine haul roads due to increasing problems of overrutting, potholes, and excessive settlement is a major issue. These problems mainly arise from the mismatch of overburden soil strength and stresses exerted by moving dumpers, inadequate compaction of soil, and improper assessment of the load-deformation characteristics of overburden soil under repeated loading. In the past, several research studies have been conducted; however, most of the studies are related to the geotechnical characterization and stabilization of mine overburden soil. In this study, the deformation characteristics, i.e., plastic and resilient deformations, of an overburden soil extracted during mining operations have been addressed, taking into account the influence of varying compaction densities, cyclic deviatoric stress, and loading frequencies. Compaction density notably affects soil strength, with 5.82% and 16.4% increases in density resulting in 23%-48% and 297%-410% strength gains, respectively. Meanwhile, cyclic deviatoric stress and confining pressure primarily influenced the axial strain behavior of mine overburden soil subjected to cyclic loading. At higher compaction densities, higher resilient modulus values were obtained. For a confining pressure of 48 kPa, increases of 5.82% and 16.4% in compaction density resulted in an increase in the resilient modulus by 32.6%-48.9%, 36.5%-67.6%, and 73%-201.3%, for increasing levels of cyclic deviatoric stress. The plastic deformations obtained were also notably high. Thus, mine overburden soils with high resilient modulus values can still experience premature failure, owing to the significant accumulation of plastic strain under high repeated deviatoric stresses. From the analysis of test results, three-parameter strain models have also been developed as a function of the number of load repetitions and the applied cyclic deviatoric stress to predict the rutting phenomenon in overburden soil at different compaction densities, applied cyclic deviatoric loads, and loading frequencies.

Under various stress paths, the deformation characteristics represented great differences. In this paper, a series of cyclic triaxial tests have been conducted with Fujian standard sand. By comparing the constant deviatoric (CDS) and constant axial stress paths (CAS), the influence mechanism of the cyclic amplitude of the deviatoric stress was discussed. The test results showed that the stress path significantly influenced the volumetric and shear strains. The increasing and decreasing trend in the volumetric strain (epsilon v) was consistent with the spherical stress (lnp). Compared with the two stress paths, the slope of the epsilon v-lnp curve during the loading and unloading stages was larger under the CAS path. In the CDS path, qc almost did not affect the cumulative volumetric strain, and in the CAS path, the effect was obvious. The shear strain curve was in accordance with the direction of the stress path. As the cyclic number increased, the shear strain gradually accumulated. The shear strain accumulation under the CAS path was larger. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. In practical engineering, the soil will experience various stress paths. For example, in slope or earth-rock dam engineering, where the water level rises and falls repeatedly, the soil often goes through the stress path of constant deviational stress with the cyclic increase and decrease in the spherical stress. In foundation pit engineering, the soil often experiences the stress path of the constant axial stress (CAS) with cyclic loading and unloading of the lateral stress. The stress path greatly influences the deformation and strength of soil. Therefore, the previous two stress paths are compared in this paper to discuss the influence of the cyclic amplitude of deviatoric stress. Under three different consolidation states, the cyclic amplitude of the deviatoric stress significantly influenced the volumetric and shear strains. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. Therefore, in practical engineering, if the stress path in the experiment differs from the actual value, the influence of the stress path should be properly considered. The results should be modified according to the degree of influence of each stress condition.

The back pressure saturation method, a widely adopted and efficient technique for enhancing soil saturation, can nonetheless introduce notable deviations in soil strength parameters. Standard spherical glass bead sand was utilized for conducting benchmark consolidated undrained (CU), consolidated drained (CD), and dry sample tests. Real-time accurate measurements and comparative analyses of deviatoric stress and pore pressure (or volumetric deformation) data were performed. Utilizing the p '-q q stress path diagram, the influence of back pressure application on soil mechanical properties was significantly demonstrated and quantitatively analyzed, thereby preliminarily elucidating the mechanism of back pressure influence. The setting of back pressure significantly impacts the results of CU tests, where the shape of pore pressure development governs the shape of deviatoric stress development, ultimately influencing the determination of strength parameters. However, the stress path remains constrained within the framework of the revised Cam-Clay model. The mode and rate of pore pressure development are primarily constrained by the magnitude of the back pressure setting and the relative density of the sample. As back pressure increases, the potential change in pore pressure also increases, resulting in a greater amplitude of deviatoric stress change. Similarly, a higher relative density leads to a faster development rate of pore pressure and an increased rate of deviatoric stress. Under identical initial conditions, the development of pore pressure in CU tests exhibits high consistency with the development of volume deformation in CD tests, revealing the common essence of the sample's volumetric deformation potential across different boundary conditions. A quantitative prediction formula for the residual strength of CU tests at the critical state is presented. The residual pore pressure value can be initially quantified based on the relative density and back pressure measurements, subsequently leading to the determination of the residual strength of CU.

This paper develops a general and complete solution for the undrained cylindrical cavity expansion problem in nonassociated Mohr-Coulomb soil under nonhydrostatic initial stress field (i.e., arbitrary K-0 values of the earth pressure coefficient), by expanding a unique and efficient graphical solution procedure recently proposed by Chen and Wang in 2022 for the special in situ stress case with K-0=1. It is interesting to find that the cavity expansion deviatoric stress path is always composed of a series of piecewise straight lines, for all different case scenarios of K-0 being involved. When the cavity is sufficiently expanded, the stress path will eventually end, exclusively, in a major sextant with Lode angle theta in between 5 pi/3 and 11 pi/6 or on the specific line of theta = 11 pi/6. The salient advantage/feature of the present general graphical approach lies in that it can deduce the cavity expansion responses in full closed form, nevertheless being free of the limitation of the intermediacy assumption for the vertical stress and of the difficulty existing in the traditional zoning method that involves cumbersome, sequential determination of distinct Mohr-Coulomb plastic regions. Some typical results for the desired cavity expansion curves and the limit cavity pressure are presented, to investigate the impacts of soil plasticity parameters and the earth pressure coefficient on the cavity responses. The proposed graphical method/solution will be of great value for the interpretation of pressuremeter tests in cohesive-frictional soils.

Mine haul roads are the unpaved roads that are constructed from the overburden materials obtained from the mining operations and are used for the movement of heavily loaded dumpers and trucks. The haul roads constructed from this overburden material shows continuous distress in the form of over ruts, potholes, and shear failures, creating major issues in the movement of dumpers. In the present research study, an experimental investigation was conducted based on mechanistic empirical design to evaluate the strength-deformation characteristics, durability, and environmental emissions of cement stabilized overburden soil of a local mine. The unconfined compression tests were conducted at cement dosages varying from 1 to 6% of dry soil mass and increase in the unconfined compressive strength were examined at different intervals of time until 28 days of the curing period. In the case of static triaxial tests, the enhancement in undrained shear strength and elastic modulus of stabilized specimens was determined in comparison to the untreated specimens, whereas in cyclic triaxial tests, the reduction in permanent deformations and increase in resilient modulus were evaluated under different confining pressures and cyclic deviatoric stresses. An empirical model has been proposed to predict the long-term rutting of overburden under repeated loading. The proposed model is based on the behaviour of various parameters, such as applied cyclic deviatoric stress, number of load repetitions, loading frequencies, and on the permanent deformation characteristic of mine overburden soil. In addition, durability and environmental sustainability aspects of the treatment has also been studied to determine the optimal dose of cement.