Mechanism of delayed leaching of heavy metals from naturally contaminated soils

Naturally contaminated soils that contain contaminants deep within the particles may show delayed leaching. To incorporate this, a novel approach for predicting the distribution of contaminants, both in the soil particle and surrounding liquid, is achieved using the finite difference method. The approach is named the 'intraparticle pore-diffusion model' and is applied to simulate the batch leaching test of heavy metal contaminated soils. Intraparticle diffusion and sorption equilibrium are considered. The desorption phenomena of heavy metal from soil particles are considered as a one-dimensional, polar-symmetric problem in the spherical coordinate system by supposing soil particles to be porous, perfect spheres. The results indicate that soil constituted of larger particles leach more contaminants at a certain time and faster for a certain leaching amount

The effect of particle shape on rockfall events

The effects of rock shape and initial orientation on the rockfall phenomena are studied using a two-dimensional polygonal discrete element method (DEM). In the simulation, rock particles with the same mass but different shapes are dropped from the same height onto a straight slope to investigate the variations in both translational and rotational kinetic energies and the runout distance. Parametric studies under varied angularity and aspect ratio of the rock revealed a significant effect of rock shape and initial orientation on the runout distance

Validation of DEM using macroscopic stress-strain behavior and microscopic particle motion in sheared granular assemblies

Validation and/or calibration of distinct element method (DEM) models is usually performed by comparing element test simulation results with the corresponding stress-strain relationships observed in the laboratory [1]. However, such a validation procedure performed at the macroscopic level does not ensure capturing the microscopic particle-level motion [2]. Thus, the reliability of the DEM model may be limited to some stress paths and may not hold when the material response becomes non-uniform for example when shear bands develop. In this study, the validity of the DEM is assessed by comparing the numerical result with experimental data considering both particle-scale behavior (including particle rotations) and macroscopic stress-strain characteristics observed in shearing tests on granular media. Biaxial shearing tests were conducted on bi-disperse granular assemblies composed of around 2700 circular particles under different confining pressures. Particle-level motions were detected by a novel image analysis technique. Particle rotations are observed to be a key mechanism for the deformation of granular materials. The results from this study suggest that to properly calibrate DEM models able to capture the mechanical behavior in a more realistic way particle scale motions observed in laboratory experiments along with macroscopic response are necessary

G-PFEM Numerical Study of the Downward Trapdoor Problem

The downward trapdoor provides a valuable framework for investigating stress distribution and ground movement during tunnel excavation. Numerous efforts have been made to devise analytical methods based on experimental observations. The area above the trapdoor experiences gravitational flow, and it becomes an active soil pressure condition with the lowering of the trapdoor. Due to the substantial discontinuous movement between the trapdoor and the adjacent stationary support, significantly discontinuous deformations arise at the boundary between the active zone above the trapdoor and the stationary zone. This complexity renders the trapdoor problem challenging by traditional continuum analysis methods. To confront this challenge, the present study employs the Particle Finite Element Method for geotechnical applications (G-PFEM) to simulate the downward trapdoor problem. The effectiveness of this approach is demonstrated by replicating a model experiment included in the literature. The simulation captures the gravitational flow of the surrounding ground as the trapdoor descends, and the numerical results, encompassing stress distributions, ground displacements, and surface settlements, closely correspond to experimental data. Moreover, to underscore the advantages of employing G-PFEM, a larger displacement is applied to the trapdoor. The results indicate significant changes in ground displacement and corresponding earth pressure as the trapdoor displacement increases, ultimately leading to substantial slope failure like large deformation

Simulation of bearing capacity of pile in crushable soil

Crushable soils such as volcanic soils, carbonate sand or decomposed granites whose grains are easily break under foundation pressure, especially, large magnitude of stresses under pile tips. When the grains are crushed, particle size distribution (PSD) varies followed by higher compressibility of these soils. Pile foundation's settlement in crushable soils tends to be increased. Nonetheless, design code for bearing capacity of pile in crushable soil is still unavailable leading to a lot of difficulties for engineers to have an appropriate foundation design. This paper introduces a constitutive model for soils which takes account of the breakage mechanics including the evolutions of PSD and the compressibility due to grain crushing. The model is implemented in a finite element code to simulate pile penetration in crushable soil. Finally, the particle breakage around pile's tip is examined

Avalanching of variously shaped DEM particles

Grains in most technically relevant granular materials are non-convex, while in discreteelement-simulations, convex particle shapes dominate. While differences in the physical behavior can be expected, the actual observables where these effects manifest are far from clear. In this research, we investigate how in a rotating two-dimensional drum, the physical behavior for rounded, irregular convex as well as non-convex shapes differs

Damage Situation of Stone Walls in Kumamoto Castle Caused by the 2016 Kumamoto Earthquake

The authors investigated the damage situation of masonry structures caused by the 2016 Kumamoto earthquake. In this paper, the damage situation of stone walls in Kumamoto castle is reported and the mechanisms of failure and collapse of stones are discussed. The 3-D laser scanner was also applied to obtain the 3D geometry and the displacement/deformation of the stone walls was analyzed by comparing with the previous measurement results before the earthquake. The 3D laser scanning results clearly show the unnatural shape of the stone walls caused by the movement of the backfill. This unnatural shape of the stone walls can be observed even in the stone walls which avoid the collapse. In the future, the evaluation of the safety/stability of the masonry walls is important for the restoration and 3D digital data obtained by 3D laser scanning technique will be useful.研究ノー

A finite strain elastoplastic constitutive model for unsaturated soils incorporating mechanisms of compaction and hydraulic collapse

Although the deformation of unsaturated soils has usually been described based on simple infinitesimal theory, simulation methods based on the rational framework of finite strain theory are attracting attention especially when solving geotechnical problems such as slope failure induced by heavy rain in which large a deformation is expected. The purpose of this study is to reformulate an existing constitutive model for unsaturated soils (Kikumoto et al., 2010) on the basis of finite strain theory. The proposed model is based on a critical state soil model, modified Cam-clay, implementing a hyperelastic model and a bilogarithmic lnv-lnP’ (v, specific volume; P’, effective mean Kirchhoff stress) relation for a finite strain. The model is incorporated with a soil water characteristic curve based on the van Genuchten model (1990) modified to be able to consider the effect of deformation of solid matrices. The key points of this model in describing the characteristics of unsaturated soils are as follows: (1) the movement of the normal consolidation line in lnv-lnP’ resulted from the degree of saturation (Q, deviatoric Kirchhoff stress), and (2) the effect of specific volume on a water retention curve. Applicability of the model is shown through element simulations of compaction and successive soaking behavior