This study introduces recent efforts of the Architectural Institute of Japan (AIJ) to develop guidelines for largeeddy simulation (LES) of pedestrian wind environments (PWEs). Reynolds-averaged Navier-Stokes (RANS) models have been widely used for predicting urban wind environments following best practice guidelines (BPGs) by Franke et al. [Int J Environ Pollut 44, 1-4 (2011)] and Tominaga et al. [J Wind Eng Ind Aerodyn 96 (10-11), 1749-1761 (2008)]. Although RANS models can predict mean wind velocity and some turbulence statistics based on empirical assumptions, LES provides higher accuracy in resolving transient turbulence structures larger than the grid scale. With increasing urbanization, understanding instantaneous complex wind and wind-related phenomena around buildings is essential for ensuring pedestrian wind comfort and safety. However, LES applications face challenges owing to a lack of BPGs. This study outlines key recommendations for simulation setups and post-processing, including domain size, building modeling, grid generation, boundary conditions, turbulence modeling, discretization, convergence criteria, and reliability evaluation. Additionally, new benchmark cases are provided to support validation for PWEs. The AIJ working group systematically evaluated LES performance across urban scenarios to ensure practical applicability while balancing computational costs. These guidelines aim to enhance prediction reliability, thereby contributing to the standardization of LES applications for PWE and advancement of computational wind engineering.
The shape effect on the mechanical behavior of breakable coarse grains at the critical state remains insufficiently understood due to the complex nature of grain crushing characteristics. In this study, a novel discrete element method (DEM) framework incorporating both realistic particle shape and breakage was presented to comprehensively reveal the competing mechanism between inherent shape effect and grain crushing behavior for coarse grain assemblies. Two groups of realistic shapes, including angular and pebble grains, along with idealized spherical grains were modeled using the bonded particle method (BPM), with model parameters calibrated against experimental data. Subsequently, triaxial shear tests were conducted to investigate the macroscopic shear behaviors of granular assembly under varying confining pressures, with particular focus on the critical state. Two distinct shape effects have been identified: (1) more irregular shapes exhibit lower crushing resistance, leading to more significant shape degradation as reflected by a higher breakage index; and (2) more irregular shapes promote stronger interlocking between particles, enhancing mechanical stability. To characterize the competition of these effects, a debonding coefficient was proposed. Three influencing regimes were distinguished by two critical debonding coefficient. From regime I to regime III, the shape effect on enhancing interlocking between particles was gradually offset by the strength reduction caused by shape-induced degradation. These findings provide a new insight into the deformation mechanisms of breakable coarse grains with complex morphology.
This study investigates the combined effects of particle morphology and the intermediate principal stress ratio b on the multiscale mechanical behavior of granular materials. Four distinct particle morphologies, ranging from nearly spherical to highly irregular, and with or without intrapores, were obtained via X-ray tomography (& micro;CT) scanning and digitally reconstructed. A series of virtual true triaxial tests with varying b values was subsequently conducted on cubic particle assemblies using the level set-discrete element method (LS-DEM). Macroscopically, both the peak and critical stress ratios exhibit a monotonic dependence on b, characterized by an initial rapid decline, followed by a gradual reduction before stabilizing. In contrast, the influence of b on dilatancy becomes significant only at relatively high values. Microscopically, the mean coordination number correlates linearly with the friction angle across all morphologies and stress conditions. Analysis of shear-induced anisotropy and particle rotation characteristics reveals that more complex morphologies promote the development of more anisotropic internal structures and restrict the rolling motion of individual particles by locking them in place to enable higher bulk strength. In contrast, increasing b reduces the contact anisotropy and facilitates particle rotation, thereby decreasing the shear resistance. These findings contribute to an improved understanding and modeling of granular materials with realistic particle morphologies under complex stress paths.
A number of empirical equations, expressing the various types of soil stiffness indices (SSIs) of compacted soil as functions of dry density rho(d) and degree of saturation S-r, are summarized in this study. They are generalized in the normalized form of SSI= C-SSIF-SSI(Delta S-r)G(SSI)([D-c](1Ec)). C-SSI is the coefficient, different for different SSI test conditions, F-SSI(Delta S-r) is a decreasing function of Delta S-r= S-r - "the optimum, (S-r)(opt)" with F-SSI(Delta S-r = 0) = 1.0, and G(SSI)([D-c](1Ec)) is an increasing function of the degree of compaction by the Standard Proctor test, [D-c](1Ec), with G(SSI)([D-c](1Ec) = 100 %) = 1.0. Under the various conditions of the data, the G(SSI) functions are rather similar, whereas the F-SSI functions are largely different. With drained SSIs evaluated at relatively low strains and relatively low confining pressures, F-SSI is considerably large when Delta S-r < 0 due to the fairly large effects of S-r on these SSIs. As a result, when S-r is in a certain range just below (S-r)(opt), the SSIs become the effective indices of water content w, rather than rho(d). The compacted water content can be estimated and controlled to remain within a narrow range centered at the target by keeping the frequently measured field SSIs between the defined upper and lower thresholds. The procedure for determining the target and the upper and lower bounds of the SSIs, based on field calibration compaction test data and relevant normalized empirical SSI equations, is explained. A simplified method is proposed, which suggests that, when field SSIs are kept between 0.5 and 2.0 times the target SSI, compacted w values are expected to be approximately maintained between 0.8 and 1.2 times the target w. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4.0/).
