Existing literature on true triaxial and torsional shear tests indicate that the mechanical response of a granular assembly is significantly influenced by the magnitude of the intermediate principal stress ratio. The present study aims to explore the mechanism behind such effects in reference to the particle-level interaction using 3D DEM simulations. In this regard, true triaxial numerical simulations have been carried out with constant minor principal stress and varying b\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$b$$\end{document} values employing rolling resistance-type contact model to mimic particle shape. The numerical simulations have been validated against the true triaxial experiments reported in the literature for dense Santa Monica beach sand. The macro-level shearing response of the granular assembly has been examined in terms of the evolution of stress ratio and volumetric strain for different rolling resistance coefficients. Further, such macro-level response has been assessed in reference to the micro-scale attributes, e.g. average contact force, number of interparticle contacts, mechanical coordination number, contact normal orientation, and fabric tensor as well as meso-scale attribute like strong contact force network. Lade's failure surface has been adopted to represent the stress and fabric at peak state in the octahedral plane, and mathematical expressions have been proposed relating the failure surface parameters to the rolling resistance coefficient.

Temporary plugging zones are low-permeability fracture-scale plugs 'assembled' in situ by injecting polymer particles into petroleum reservoirs. We applied the rolling resistance linear model to simulate the shear strength of a rectangular packed bed, our model for a temporary plugging zone, comprising either uniform-sized particles or a binary mixture of larger bridging particles and smaller filling particles. Simulation results show that the strength of uniform beds increases with the size, the aspect ratio, the friction coefficient, and the Young's modulus of the particles. The strength of binary packed beds first increased and then decreased as the fractional volume of the domain occupied by filling particles increased. Maximum strength was achieved when bridging particles have uniform Young's modulus and aspect ratio but a range of friction coefficients, and their friction coefficient, Young's modulus and aspect ratio are 21%, 17% and 18% larger than those of filling particles.

The interaction between off-road vehicles and terrain in forestry operations has been extensively studied to assess machine performance and soil damage, emphasizing the importance of the relationship between machine mobility and terrain conditions. This study assesses the rolling resistance coefficient (mu r) using engine data acquired through CAN-bus systems and the J1939 standard. The aim is to determine whether soil-machine interactions can be detected by modeling rolling resistance coefficients with a simple approach based on machine parameters and essential terrain characteristics. The study was conducted on a forwarder (John Deere (R) 1210G) across different terrain surfaces and load conditions. CAN-bus data were processed, while terrain characteristics and slope were determined using high-accuracy spatial data. The activities consisted of (i) a calibration test to evaluate the model's sensitivity and (ii) a field test in a real working scenario. The developed methodology demonstrated sufficient sensitivity to detect increasing rolling resistance values on rougher surfaces, highlighting the impact of surface type on forwarder operations. Field tests revealed lower rolling resistance values for the unloaded forwarder (between 0.15 and 0.3) than loaded conditions (from 0.4 to 0.6). The model reliably captured mu r changes between consecutive drives and skids, particularly during uphill operations, with significant differences influenced by trail conditions and forwarder interactions rather than just load. By providing a practical methodology for assessing off-road machine performance and its impact on driving surfaces, the study highlights the importance of understanding off-road vehicle dynamics for informed operation planning decisions. This study underscores that integrating real-time mobility data from CAN-bus technology with terrain analysis enhances operational efficiency and helps minimize soil damage, thereby supporting more sustainable forest management practices.

The coefficient of lateral earth pressure at rest, K-0, is an essential parameter for analyzing earth pressure distribution and the safe reliability of structures in geotechnical engineering. This paper presents a series of numerical one-dimensional compression tests on granular soils with particle size distribution (PSD) and rolling resistance (RR) effects using a real-particle 3D discrete element model. The corresponding macro-micro behaviors are investigated in a parallel way. Both PSD and RR affect K-0 and the related compression characteristics. A higher coefficient of uniformity (C-u) or rolling resistance coefficient (mu(r)) results in a monotonic decrease in the mean coordination number, and too much consideration of RR makes the mean coordination number less realistic in a particle system. The influence of PSD is more sensitive to the local-ordering structure and contact force network than the RR. The inhomogeneity of normal contact forces enhances as C-u increases and slightly reduces as mu(r) increases. The strong contacts are much more anisotropic than the weak ones. Specimen with lower C-u or higher mu(r) induces higher anisotropy and more strong contacts during compression, in which a lower K-0 is measured. A unique macro-micro relationship exists between K-0 and deviatoric fabric when strong contacts are considered only.

This paper presents the assessment of selected tractor tires used in forest conditions. The first element of this assessment is related to tractive properties, while the second part concerns the potential negative impact of the tires on the ground. The research was conducted on the skid trail located in a lowland pine stand in Poland (Lower Silesian District). The 9.5-24, 400/55-22.5 and 11.2R24 tires were used for the experiment, and the following tractive parameters were analyzed: traction force, pulling force and rolling resistance. These parameters were determined during the experiment using special measure stand mounted on a 3-point linkage of the tractor. In addition to the traction properties, the impact of the wheel on the ground was determined - this evaluation included measurements of footprint areas and calculation of contact pressures. Based on the obtained results, it was shown that the increase of the vertical load and reduction of the inflation pressure of tires can cause an increase in net traction force of as much as 35% and 16%, respectively. The analysis of contact areas and pressures showed that the widest tire (400/55-22.5) had the least negative impact on the ground. The reducing of inflation pressure allowed to obtain higher traction force, higher contact area and smaller contact pressures.