Micromechanics of shear wave propagation and small-strain stiffness in granular soil
Started: February 2016
Supervisor: O'Sullivan, C.
Funding: Vied-Newton PhD Scholarship and Dixon Scholarship
The small-strain stiffness of soil has been considered in a number of soil mechanics research studies. Many factors influence stiffness, including the properties of grains, the material fabric and stress state. This research will focus on the influence of a three dimensional stress state on soil stiffness and on the basis for the correction factor for packing density that is routinely used in soil mechanics test interpretation.
In this research, the shear and compression stiffnesses will be inferred by considering the compression and shear wave velocities, Vp and Vs respectively. Stress wave propagation through granular materials is a complicated problem because of their inherent discrete nature as noted by Marketos & O’Sullivan (2013). An analysis of the particle-scale data produced during discrete element method (DEM) simulations of wave propagation will provide significant insight into shear wave propagation. This study aims to develop a micromechanics based description of shear wave propagation in soil considering the influence of particle size distribution on the dynamic properties of material including dispersion and maximum frequency at which the wave can be transmitted. A modified version of the open-source code, Granular LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) will be used in the research to investigate the effect of particle properties on attenuation of the stress wave magnitude.
- Examine the influence of a non-isotropic, true triaxial stress state on soil stiffness.
- Suggest an appropriate correction factor based on a void ratio function and the sensitivity of relationship between shear modulus and isotropic confining stress.
- Understand the influence of particle size distribution (non-uniform spheres in DEM models) on the dynamic properties of material including dispersion and maximum frequency that can be transmitted.
- Investigate the effect of soil particle morphology (spherical, non-spherical particles and surface roughness) on shear wave propagation.
- Understand the impact of the particle properties (density, inter-particle friction, shear modulus, Poisson’s ratio) on attenuation of the shear wave magnitude.
- Develop contact models that consider the size and shape of a soil particle in an open-source code, Granular LAMMPS as proposed by Plimpton (1995).
- Huang, X, O’Sullivan, C, Hanley, K.J & Kwok, C.Y. (2016). Partition of the contact force network obtained in discrete element simulations of element tests. Computational Particle Mechanics, Vol. 1, No. 1, pp.1-8.
- Otsubo, M, O'Sullivan, C, Sim W.W & Ibraim, E. (2015). Quantitative assessment of the influence of surface roughnesson soil stiffness. Geotechnique, Vol. 65, No. 8, pp. 694-700.
- O'Donovan, J, O'Sullivan, C, Marketos, G & Wood D.M. (2015). Anisotropic stress and shear wave velocity: DEM studies of a crystalline granular material. Geotechnique letters, Vol. 5, No. 3, pp: 224-230.
- Marketos, G & O’Sullivan, C. (2013). A micromechanics-based analytical method for wave propagation through a granular material. Soil Dynamics and Earthquake Engineering, Vol. 45, pp.25–34.
- Bellotti, R, Jamiolkowski, M, Lo Priesti, D.C.F & O'neil D.A. (1996). Anisotropy of small strain stiffness in Ticino sand. Geotechnique, Vol. 46, No. 1, pp. 115-131.
- Plimpton, S. (1995). Fast parallel algorithms for short-range molecular dynamics. Journal of computational physics, Vol.117, No. 1, pp. 1-19.
PhD Candidate - Geotechnics
Department of Civil & Environmental Engineering
Imperial College London SW7 2AZ