Masahide Otsubo

Micromechanics of shear wave propagation in soil

Started: October 2013
Supervisor: O'Sullivan, C.; Sim, W.W.
Funding: Japan Student Services Organization (JASSO) and DIXON scholarship

Background

The stiffness of soils at very small strains is important to evaluate the performance of soil under static and dynamic loading. The stiffness value depends upon a number of factors, such as the magnitude of confining pressure, particle characteristics and the state of particle packing.

The velocity of elastic wave propagation in soil links to the small strain stiffness of the soil. Techniques using bender elements have been developed to measure the wave velocity in soil, enabling us to develop a theory for the wave propagation through soil.

In general, soil mechanics does not take the influence of surface roughness of its constituant soil particles into account despite the real contacting surfaces rarely being smooth. This study aims to develop the micromechanics of shear wave propagation in soil considering the influence of the surface roughness of the soil grains. An experimental study using bender elements will be conducted where spherical ballotini are used (Fig. 1).

The discrete element method (DEM) is a powerful tool that can relate particle-scale behaviour at contacts with the overall response of soil. Increased computational power enables us to simulate more realistic contact models which consider the surface roughness in DEM. An open-source DEM code, LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) will be used to simulate experiments which will be conducted in this study. 

Research aims

• Develop a methodology for accurate measurements of surface roughness of a soil particle using an interferometer.
• Quantify the change of surface roughness at various confining pressures.
• Understand the influence of the surface roughness of a soil particle on the shear wave propagation under various confining pressures using bender element tests.
• Implement contact models which consider the surface roughness of a soil particle in an open-source DEM code, LAMMPS.
• Simulate the bender element tests in LAMMPS and compare them with equivalent experiments.

MASAHIDE OTSUBO

PhD Candidate - Geotechnics 
Department of Civil & Environmental Engineering 
Imperial College London SW7 2AZ
m.otsubo13@imperial.ac.uk