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.

This study presents a series of centrifuge model tests that were conducted to investigate the grouting mechanism and its effect during rectangular pipe jacking in soft soil. A new jacking grouting device was developed to simulate the entire grouting process in the centrifuge model tests. The influence of grouting on the friction at the lining-soil interface and vertical displacement of the tunnel lining was analysed. In addition, the impact of the grouting slurry's viscosity and fluid loss on ground surface settlement and the friction at the pipe-soil interface was also examined. The results indicate that grouting plays a significant role in mitigating the friction and vertical displacement of the tunnel lining caused by excavation. Furthermore, the study shows that reducing the viscosity of the grouting slurry can reduce the friction coefficient at the pipe-soil interface, thus facilitating the advancement of pipe jacking. The use of a low fluid loss grouting slurry is also recommended to improve control over ground surface settlement. These findings are crucial for enhancing the efficiency and safety of rectangular pipe jacking in soft soil.

Introduction. The task of high-quality cleaning of root crops from soil is relevant at all stages of preparing roots for further processing, feeding to animals, and selling. In the machines for cleaning root crops from soil, there is mostly used water. With the water consumption for washing a unit of mass of soiled root crops up to 200-400%, the use of water creates a huge problem including soiled water treatment. The dry method of cleaning root crops is most common in practice and involves the use of appropriate machines, which are not always able to provide the required quality of the finished product. Therefore, the problem of developing a root crop cleaner by the dry cleaning method and substantiating the cleaner optimal parameters to ensure the required quality of the finished product is important and relevant. Aim of the Study. The study is aimed at substantiating theoretically the parameters of a root cleaner with adjacent rollers rotating at different frequencies. Materials and Methods. The subject of the study is the technological process of cleaning root crops with the dry method. To realize this process, there has been developed a cleaner of root crops from soil, the key features of which are the use of a roller transport-cleaning working element and the ability of adjacent rollers rotate at different frequencies. Individual design parameters of the proposed cleaner have been substantiated theoretically. Results. There have been determined the forces acting on the root crop when it is located on rotating rollers. There has been found the dependence of the angular displacement phi(t), angular velocity omega(t) of the root crop located on rotating rollers, and the dependence of the coefficient of root crop sliding friction on the rollers on the angle alpha, which determines the relationship between the main design parameters of the working element, in particular, the diameter of the rollers and the distance between them, and the physical and mechanical properties of the root crops. Discussion and Conclusion. The studies of the root crop cleaner conducted in laboratory conditions have confirmed the results of theoretical studies and showed that with a length of the transport-cleaning working element of 2 m within a time of 34,4 s it is possible to achieve an efficient cleaning of 78% when the cleaner is equipped with 16 rollers and the ratio of the rotation frequencies for odd and even rollers is 220/250 min-1. The study results are useful for creating and modernizing technical means for post-harvest processing of root crops, conducting further studies on technological improvement of similar means of mechanization of agricultural processes, and for using in the educational process to train technical specialists.

The injection of large volumes of natural gas into geological formations, as is required for underground gas storage, leads to alterations in the effective stress exerted on adjacent faults. This increases the potential for their reactivation and subsequent earthquake triggering. Most measurements of the frictional properties of rock fractures have been conducted under normal and shear stresses. However, faults in gas storage facilities exist within a true three-dimensional (3D) stress state. A double-direct shear experiment on rock fractures under both lateral and normal stresses was conducted using a true triaxial loading system. It was observed that the friction coefficient increases with increasing lateral stress, but decreases with increasing normal stress. The impact of lateral and normal stresses on the response is primarily mediated through their influence on the initial friction coefficient. This allows for an empirical modification of the rate-state friction model that considers the influence of lateral and normal stresses. The impact of lateral and normal stresses on observed friction coefficients is related to the propensity for the production of wear products on the fracture surfaces. Lateral stresses enhance the shear strength of rock (e.g. Mogi criterion). This reduces asperity breakage and the generation of wear products, and consequently augments the friction coefficient of the surface. Conversely, increased normal stresses inhibit dilatancy on the fracture surface, increasing the breakage of asperities and the concomitant production of wear products that promote rolling deformation. This ultimately reduces the friction coefficient. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Interparticle friction is an intrinsic property of particles, which plays an important role in the macroscopic and microscopic shear mechanical properties of granular materials. In this research, we investigate the shear behavior of granular materials with different friction coefficients using ring shear tests. The particle image velocimetry (PIV) technique was also used to analyze the shear flow characteristics. The results indicate that the peak shear strength of granular materials increases with the increase in shear rates, especially for granular materials with high friction coefficients. The shear stress fluctuation difference is smaller under low normal stress. Under high normal stress, the shear stress fluctuation of granular materials with high friction coefficient is higher than that of granular materials with low friction coefficient. In addition, the shear stress fluctuation shows a trend of increasing with the increase of shear rates. The range of the liquid phase flow region of granular materials decreases with the increase of friction coefficient and normal stress. This work reveals the shear flow characteristics of granular materials under different conditions, which can provide reference for the flow processes of geological disasters such as landslides and debris flows.