M. Otsubo 교수

This contribution considers the critical time increment (Δtcrit) to achieve stable simulations using particulate discrete element method (DEM) codes that adopt a Verlet-type time integration scheme. The Δtcrit is determined by considering the maximum vibration frequency of the system. Based on a series of parametric studies, Δtcrit is shown to depend on the particle mass (m), the maximum contact stiffness (Kmax), and the maximum particle coordination number (CN,max). Empirical expressions relati

The nature of soil stiffness at small strains remains poorly understood. The relationship between soil stiffness (e.g. shear stiffness, G 0 ) and isotropic confining pressure (p′) can be described using a power function with exponent (b), that is, G 0 = A (p′/p r ) b , where A is a constant and p r is an arbitrary reference pressure. Experimentally determined values of b are usually around 0·5 and these are higher than the value of 0·33 that can be analytically determined using Hertzian theory.

This contribution assesses the effect of particle surface roughness on the shear wave velocity (VS) and the small-strain stiffness (G0) of soils using both laboratory shear plate dynamic tests and discrete element method (DEM) analyses. Roughness is both controlled and quantified to develop a more comprehensive understanding than was achieved in prior contributions that involved binary comparisons of rough and smooth particles. Glass beads were tested to isolate surface roughness effects from ot

Discrete-element method (DEM) simulations of planar wave propagation are used to examine the effect of particle surface roughness on the stiffness and dynamic response of granular materials. A new contact model that considers particle surface roughness is implemented in the DEM simulations. Face-centred cubic lattice packings and random configurations are used; uniform spheres are considered in both cases to isolate fabric and contact model effects from inertia effects. For the range of values c

The behaviour of gap-graded granular materials – that is, mixtures of coarse and cohesionless finer grains with measurable differences in particle size – does not always conform to established frameworks of sand behaviour. Prior research has revealed that the role of the finer particles on the stress–strain response, liquefaction resistance and internal stability of non-cohesive gap-graded soils is significant and complex, and highly dependent on both the volumetric proportion of finer particles

This paper describes a novel method to separate the leakage current, obtained in polymeric materials during a salt fog aging test, into three components of conductive current, corona discharge current and dry band arc discharge current. First, we investigated that the relationship between optical emissions due to discharges and a leakage current. Based on experimentally defined discharge types, the separation of the leakage current was carried out. Finally, the polymer surface was analyzed using

The liquefaction phenomena of sands have been studied by many researchers to date. Laboratory element tests have revealed key factors that govern liquefaction phenomena, such as relative density, particle size distribution, and grain shape. However, challenges remain in quantifying inherent anisotropy and in evaluating its impact on liquefaction phenomena. This contribution explores the effect of inherent anisotropy on the mechanical response of granular materials using the discrete element meth

Soils are granular materials consisting of many particles, and the overall response of a soil can be considered to be a complex accumulation of the inter-particle responses. Small-strain soil stiffness is important to predict the ground deformation in situ and in practice and is often deduced from elastic wave velocity in laboratory experiments. The dynamic properties of soils are also important for dynamic analyses including site response analysis. Stress waves propagate through soil via the gr

The dynamic response of gap-graded soils is complex; it requires massive experimental and theoretical investigation in order for a sound understanding to be developed. The complexity of the behaviour of such soils arises partially due to the presence of many influential parameters, such as the finer sand/silt content (Fs), size ratio (Rd), and void ratio (e). In this contribution, experiments are conducted on a series of gap-graded soil mixtures, where the coarser sand is mixed with four differe

Laboratory geophysics tests including bender elements and acoustic emission measure the speed of propagation of stress or sound waves in granular materials to derive elastic stiffness parameters. This contribution builds on earlier studies to assess whether the received signal characteristics can provide additional information about either the material's behaviour or the nature of the material itself. Specifically it considers the maximum frequency that the material can transmit; it also assesse