Clay pellet mixtures are generally compressed to improve their engineering performance. Deepening the comprehension of the mechanical properties of these mixtures in the complete compression process facilitates the benefit to the engineering design and their utilization. In this study, the effects of soil grain size distribution, water content and dry density on the mechanical properties and microstructure of Teguline clay pellet mixtures during a continuous oedometric compression process are explored. Three types of soil pellet mixtures, including mixture A (grain size <= 5 mm), mixture B (<= 0.4 mm) and mixture C (2-5 mm), were prepared with different water contents of 7%, 8% and 12% respectively. Subsequently, continuous oedometeric compression was undertaken to explore their mechanical behaviours of the soil pellet mixtures. After that, the microstropic structures of the compacted pellet mixtures were investigated using mercury intrusion porosimetry (MIP). The results indicated that mixture A has a minimal initial packing density of pellet mixtures, while mixture C has a maximum one at the initial compression stage. After completion of compression, the compression curves of the pellet mixtures tended to converge uniformity at a semilogarithm coordinate as the vertical stress increased. All of the compression curves presented a concave shape at the plastic compression stage, which is significantly influenced by grain size distribution and water content. In contrast, the elastic compression and rebound behaviours are little affected by the grain size distribution and water content. As far as the microstructure is concerned, compacted samples prepared by mixture A or C presented a unimodal pore structure, while those by mixture B showcased a bimodal pore structure. In comparison with the unimodal pore distribution of the undisturbed stiff clay, the compacted samples displayed a pseudo-unimodal pore distribution because the inter-aggregate pores still existed. A double tangent method was proposed to determine the delimiting pore diameter of the pseudounimodal pore distribution curves and found that the delimiting pore diameter decreased with the increase of dry density and water content. Moreover, the inflexion point for the pore diameter of compacted samples prepared by coarse soil was larger than that of fine soil. Combining this work with previous research, it was found that the high compression of coarse soil easily causes the pseudo-unimodal shape, which is also impacted by water content and particle properties. This work could help deepen the understanding of the mechanical characteristics and microstructure of the stiff clay pellet mixtures during continuous oedometric compression.

Design of geosystems built on coarse-grained soils with broader gradations are typically based on methodologies developed for clean sands without explicit consideration of the effects of gradation, potentially leading to uncertainty in performance predictions. This study investigates the effect of changes in gradation on the shear strength, stress-dilatancy behavior, critical state parameters, and fabric evolution of coarse-grained soils using three-dimensional (3D) discrete element method (DEM) simulations. The simulations of monotonic isotropically-consolidated drained and undrained triaxial tests were conducted on specimens with coefficients of uniformity (CU) between 1.9 and 6.4 composed of nonspherical particles following the calibration of parameters against experimental triaxial data. Results are used to evaluate the peak and critical state shear strengths, dilatancy responses, critical state lines, shear-induced pore pressures, and fabric evolution. Notably, an increase in CU leads to increases in peak shear strength, total dilation, rate of dilation, negative pore pressure magnitude, and rate of pore pressure generation. The results show that the state parameter better captures the effect of gradation than the relative density because the former accounts for the difference between the initial and critical states. The trends in triaxial parameters are compared with established frameworks to highlight the differences in response resulting from variations in CU. The particle-level measurements indicate that gradation affects the packing characteristics and contact force transmission, where broader gradations result in greater interlocking between coarser particles, and the presence of coarser particles increases the anisotropy of the strong force networks. The finer particles provide resistance to buckling within these strong force networks. Additionally, particles smaller than D10 are inactive in stress transmission, and the percentage of particles inactive in stress transmission decreases with an increasing CU. The combination of macro- and microresults contributes to understanding the mobilization of stress and its dependency on dilatancy in soils of varying gradation.

Freeze-thaw cycles are prevalent climatic phenomena with substantial effects on soils, leading to alterations in soil strength, stiffness, and hydraulic properties due to disruptions in the soil structure. With the ongoing climate change, weather patterns have grown progressively erratic, resulting in more frequent occurrences of extreme weather events, including heavy snowfall, intense rainfall, and windstorms, even in regions characterized typically with mild climates across the globe. The climate change can potentially threat manmade infrastructure constructed within or upon local soils, regardless of their susceptibility to freezing in temperate climates. The principal objective of this study is to assess the influence of freeze-thaw cycles on the California Bearing Ratio (CBR %) across 12 distinct soils with variations in granulometry and mineralogy. The freeze-thaw cycles resulted in a notable decrease in CBR (%) within the range of 40% to 70%. A strong inverse correlation with D50 was observed regarding the decrease in CBR (%). Nevertheless, it was discerned that the decrease in CBR (%) subsequent to freeze-thaw cycles varied among soil samples sharing identical D50 and liquid limit characteristics. The aim of this study is to enhance our comprehension of how freeze-thaw cycles can impact the bearing capacity of these soils, thereby providing essential insights for predicting their behavior and potential influence on infrastructure in the context of climate change.

The Matmata region, located in the south of Gab & egrave;s (Tunisia), experienced significant damage during the floods of the Beni zelten wadi on November 11, 2017. These floods, exacerbated by the steep slopes and underlying soil conditions, led to the occurrence of debris flows, posing a threat to road infrastructure. The generation of debris flows is closely linked to intense rainfall events that surpass the soil capacity to retain water. To gain insights into the behaviour of the soil samples, various characteristics were analysed, including texture, clay mineralogy, grain size distribution, and Atterberg limits. The results showed that the mean liquid limit values ranged from 38% to 62%, while the mean plasticity index of the materials in the landslide-prone areas varied from 18% to 27.9%. These findings indicate presence of clay formations and highlight a significance of the increased soil clay content as contributing factors to landslide development. The X-ray Diffraction analysis revealed that gypsum, quartz, phyllosilicate and calcite minerals were the most abundant minerals identified in the soil samples. This work shows the importance of clay mineral and geotechnical parameters of the soils in the occurrence of landslides and predicting debris flows occurrences in the Matmata region.