Particle segregation is a widespread phenomenon in nature. Vertical vibration systems have been a focal point in studying particle segregation, providing valuable insights into the mechanisms and patterns that influence this process. However, despite extensive research on the mechanisms and patterns of particle separation, the consequences, particularly the mechanical properties of samples resulting from particle segregation, remain less understood. This study aims to investigate the segregation process of a binary mixture under vertical vibration and examine the consequences through monotonic and cyclic triaxial drained tests. The results reveal that large and small particles segregate nearly simultaneously, with more thorough separation observed for large particles. The segregation index, Ds, effectively describes this evolution process, offering a quantitative metric for both mixing and segregation. Granular temperature analysis unveils three distinct states during segregation: solid-like, fluid-like, and solid-liquid transitional phase, corresponding to varying activity levels of particle segregation. Drained triaxial shear tests demonstrate the sensitivity of stress-strain relationships to the degree of segregation. Interestingly, ultimate strength is found to be essentially unrelated to the degree of segregation. When the segregation index approaches zero, signifying particles approaching a uniform distribution, the granular system reaches a harmonic state. This state exhibits optimal mechanical performance characterised by maximum peak stress, friction angle, and the highest elastic modulus. These findings underscore the potential impact of segregation on the mechanical response of granular mixtures and emphasise the necessity of a comprehensive understanding of particle segregation in soil mechanics.

The granular column collapse is a simple model to study natural disasters such as landslides, rock avalanches, and debris flows because of its potential to provide solid links of physical and mechanical properties to these catastrophic flows. Such flows are commonly composed of different grain-size distributions, namely, polydispersity. Owing to the complexity of different particle-size phases, explanations of the collapse dynamics, run out distance, and size-segregation behavior of granular flows remain elusive. A binary-size mixture of granular materials is well-known as a simplified version of particle-size distribution. This paper explores the effects of the large-particle content on the collapse mobility, deposition morphology, and size segregation of binary-size mixtures composed in each column geometry. Although the kinetic energy and deposition morphology are nearly insensitive to the content of large particles for each column geometry, the large and small particle-size phases govern differently on total kinetic energy. Remarkably, the contribution of these two particle phases to the kinetic energy is similar when the large-particle content reaches around 10% for all column geometries. By quantifying the difference of the apparent friction coefficient of small and large particle phases, the size-segregation degree of binary-size mixtures is evaluated. The results noted that the segregation degree increases exponentially with increasing the large-particle content, but it is nearly independent of the column geometry. These findings complement insights into the flow properties of geological hazards, leading to offering valuable evidence for the management of natural disasters such as landslides and debris flows.

Most of the world's railways are on ballasted track-a versatile and cost-effective support solution that can be traced back to the nineteenth century. In the twenty-first century, heavier and faster trains (freight and passenger) create higher loads and maintenance requirements. Ballast degradation becomes an important issue and solutions to increase time intervals between maintenance interventions are necessary. Some proposals involve the incorporation of elastic elements such as crumb rubber mixtures in the ballast. The crumb rubber reduces dilatancy and particle breakage. However, there is a lack of consensus on some key parameters. For example, the optimum percentage of crumb rubber in ballast is often given as 10%, which results in beneficial changes in the stiffness and energy absorption properties of ballast. However, some studies refer to 10% by volume, while others refer to 10% by weight. This leads to very different outcomes, as 10% by weight is nearly double 10% by volume of the soil particles. The paper analyses the influence of incorporating crumb rubber with two different sizes of particle, at 10% by weight and 10% by volume of mineral particles, into 1/3 scaled ballast. The addition of crumb rubber densifies the natural volumetric packing of 1/3 scaled ballast. The maximum (e(max)) and minimum (e(min)) void ratios decreased for all situations tested. This is explained in part by voids filling. Under cyclic loading, crumb rubber segregation was observed.

Permafrost is strongly associated with human well-being and has become a frontier of cryospheric science. Professor Guodong Cheng is one of the most outstanding geocryologists in China. He was elected as an academician of the Chinese Academy of Sciences in 1993 and served as the president of the International Permafrost Association from 1993-1998. In the early 1980s, Professor Cheng proposed the hypothesis of the repeated-segregation mechanism for the formation of thick-layered ground ice near the permafrost table. Subsequently, in the early 2000s, he proposed the proactive roadbed cooling concept and led the successful development of a series of specific engineering measures that were fully applied in the Qinghai-Tibet Railway Project. Furthermore, he developed a conceptual model to describe the influences of changing permafrost on the groundwater system and discovered the sink-holing effect (channeling with improved hydraulic conductivity of warming permafrost). Professor Cheng has also developed theories on the three-dimensional zonation and proposed a classification system and an altitude model for high-altitude permafrost distribution. On this special occasion of Professor Cheng's 80th birthday, this paper summarizes his outstanding achievements on permafrost science, hoping the permafrost research community will carry forward the momentum to further advance permafrost science worldwide.

Particle segregation in the feeding system is a critical issue, leading to the nonuniform distribution of particles inside the flash smelting furnace and subsequently resulting in the production of unreacted materials. This study employs DEM to investigate the flow and segregation of concentrate particles in a scaled feeding system. The numerical simulations, based on calibrated parameters, are validated against two experiments, demonstrating good agreement. The influences of feeding rate, chute width, and sloping angle on particle segregation are analyzed. The severest segregation is obtained under the current operating parameter in metallurgical plants. Further increasing the feeding rate will not result in a continuous worsening of segregation. Notably, it is confirmed that increasing the chute sloping angle can largely reduce particle segregation. Meanwhile, segregation can also be reduced by narrowing the chute width; however, this leads to more particle accumulation at the periphery, potentially impacting subsequent dispersion within the furnace.

During shield construction in underground spaces, synchronous grouting slurry is poured between the surrounding rock and tunnel lining to ensure stability. For synchronous grouting slurries, few studies have investigated the relationship between the rheological parameters and physical properties, grout-segregation mechanism, and anti-segregation performance. Therefore, we explored the relationships between the slurry rheological parameters, segregation rate, and bleeding rate. Cement, sand, fly ash, and bentonite were used to prepare the slurry, and the effects of different polycarboxylate water-reducing agents and dispersible latex powder dosages were studied. The rheological parameters of 16 groups of uniformly designed slurries were tested, and the data were fit using the Herschel-Bulkley model. The optimal mix ratio lowered the slurry segregation rate, and its rheological behaviour was consistent with the Herschel-Bulkley fluid characteristics. High-yield-shear-stress synchronous grouting slurries with high and low viscosity coefficients were less likely to bleed and segregate, respectively. The optimised slurry fluidity, 3 h bleeding rate, 24 h bleeding rate, segregation rate, coagulation time, and 28 days compressive strength were 257.5 mm, 0.71%, 0.36%, 3.1%, 6.7 h, and 2.61 MPa, respectively, which meet the requirements of a synchronous grouting slurry of shield tunnels for sufficiently preventing soil disturbance and deformation in areas surrounding underground construction sites.

The fabric structure and dynamic behaviour of granular materials have been extensively studied in geotechnical engineering due to their considerable impact on permeability and mechanical properties. However, particle segregation, causing significant structural changes, remains inadequately understood, especially concerning its dynamic evolution in both global and local segregation processes. This study aims to investigate the motion of particles and evolution of internal microstructure in binary mixtures under vibrational conditions. The emphasis lies in comprehending both global and local time segregation processes, along with elucidating the potential underlying mechanisms. Through DEM simulations, it is observed that large particles tend to rise to the surface of the container while small particles aggregate at the bottom, resulting in the well-known Brazil Nut Effect. As the vibration intensity increases, the degree of segregation becomes more pronounced. Vertical segregation precedes radial segregation and eventually leads to stable separation of the binary mixture. To comprehensively analyse the segregation behaviour, we introduce a segregation index and reveal a correlation between vertical and radial segregation. Additionally, the ascending process exhibits characteristics similar to compressed solid blocks, while the descending process resembles fluid-like behaviour, suggesting a phase transition phenomenon during particle segregation. The study further highlights the role of pore filling and convective rolling as driving mechanisms for particle segregation. These findings emphasize the potential impact of external disturbances on the microstructure of granular mixtures, with implications for scenarios such as earthquakes, debris flows, and traffic loads.

A quantification of rock weathering by freeze-thaw processes in alpine rocks requires at least rock temperature data in high temporal resolution, in high quality, and over a sufficient period of time. In this study up to nine years of rock temperature data (2006-2015) from eleven rock monitoring sites in two of the highest mountain ranges of Austria were analyzed. Data were recorded at a half-hourly or hourly logging interval and at rock depths of 3, 10, and 30-40 cm. These data have been used to quantify mean conditions, ranges, and relationships of the potential near-surface weathering by freeze-thaw action considering volumetric-expansion of ice and ice segregation. For the former, freeze-thaw cycles and effective freeze-thaw cycles for frost shattering have been considered. For the latter, the intensity and duration of freezing events as well as time within the frost cracking window' have been analyzed. Results show that the eleven sites are in rather extreme topoclimatic positions and hence represent some of the highest and coolest parts of Austria and therefore the Eastern Alps. Only four sites are presumably affected by permafrost. Most sites are influenced by a long-lasting seasonal snow cover. Freeze-thaw cycles and effective freeze-thaw cycles for frost shattering are mainly affecting the near-surface and are unimportant at few tens of centimeters below the rock surface. The lowest temperatures during freezing events and the shortest freezing events have been quantified at all eleven monitoring sites very close to the surface. The time within the frost cracking window decreases in most cases from the rock surface inwards apart from very cold years/sites with very low temperatures close to the surface. As shown by this study and predicted climate change scenarios, assumed warmer rock temperature conditions in the future at alpine rock walls in Austria will lead to less severe freezing events and to shorter time periods within the frost-cracking window. Statistical correlation analyses showed furthermore that the longer the duration of the seasonal snow cover, the fewer are freeze-thaw cycles, the fewer are effective freeze-thaw cycles, the longer is the mean and the maximum duration of freezing events, and the lower is the mean annual ground temperature. The interaction of the winter snow cover history and the winter thermal regime has a complex effect on the duration of the frost cracking window but also on the number of freeze-thaw cycles as shown by a conceptual model. Predicted future warmer and snow-depleted winters in the European Alps will therefore have a complex impact on the potential weathering of alpine rocks by frost action which makes potential weathering predictions difficult. Neglecting rock moisture and rock properties in determining rock weathering limits the usefulness of solely rock temperature data. However, rock temperature data allow getting an estimate about potential weathering by freeze-thaw action which is often substantially more than previously known. (c) 2017 Elsevier B.V. All rights reserved.

We describe the introduction of several new techniques to measure and monitor permafrost properties at a site near the east coast of the Hudson Bay, northern Quebec. Eight boreholes were sunk through a lithalsa to the permafrost base. High precision temperature sensors and a pressure sensor were installed in six boreholes to monitor the long-time changes of the thermal field of the permafrost and internal pore pressure. Two open boreholes were used to carry out a ground penetrating radar transillumination survey to provide a tomographic image of the spatial distribution of electromagnetic wave velocities within the lithalsa. Cores taken from the permafrost below the active layer of the lithalsa show numerous oblique and fractured ice lenses indicative of extensive deformation of the lithalsa during its evolution. Examples of results of the new techniques applied in this study are provided. These techniques appear as very promising for permafrost studies in general. Copyright (C) 2003 John Wiley Sons, Ltd.