Effects of Particle 3D Shape on Packing Density, Critical State, Static Instability and Liquefaction of Sands Using a Proposed ‘Relative State Parameter’

The size, shape and mineral of soil particles have a big impact on the macroscale mechanical behaviour of the soil mass. The particle 3D shape characteristics (i.e., aspect ratio, sphericity, ellipsoidal degree and regularity) are investigated by the X-ray micro-tomography on crushed and natural sands. Experiments of the extreme packing densities are carried out on more than 50 samples of different kinds or gradations of clean sands and mixed silty sands. The notable dependences of both the extreme void ratios and the packing indexes are on the aspect ratio of particles. The static compression triaxial experiments under both drained and undrained shearing conditions are performed on four kinds of uniformly graded sands with different particle shapes. The most notable effect of sphericity is on the friction angle at critical state, while the most notable effect of ellipsoidal degree is on the void ratio intercept of the CSL in the power-law form. The static instability and the liquefaction behaviour of sands with rounded particles are more susceptible than sands with angular particles based on a novel proposed ‘relative state parameter’.