Particle-size control on the structure and collapsibility of sediments formed by air-fall deposition.

• Particle-size effects on aeolian deposition and sediment structure were examined. • Two distinct structures form during air-fall deposition as particle sizes vary. • The relevance between interparticle forces and gravity control structure formation. • A dimensionless granular bond number Bo captures the relevance of governing forces. • Open and collapsible structures form due to special accumulation behavior at Bo < 10. Aeolian deposition is significant to the landscape formation on Earth and even other planetary bodies. Particle size controls the transport distance of particles. However, the understanding of particle-size effects on the structure and mechanical behavior of aeolian accumulations remains limited. We investigate the effect of particle size on the structure and collapse of aeolian sediments by one-dimensional compression and collapse tests following the initial air-fall deposition of particles of various sizes from sand to fine silt. Results reveal that the relevance between interparticle forces and gravity controls the formation of two distinct sediment structures as the particle size varies. A loose structure with a packing density close to the simple cubic packing forms for sands and is not collapsible. An open structure with higher porosity forms as particle size becomes smaller. The structure can stack vertically. The stacking height, porosity, and collapsibility increase as particle size decreases. A dimensionless granular bond number Bo captures the relevance between van der Waals forces and gravity. A threshold particle size corresponding to Bo = 10 is identified, below which open and collapsible structures form. The structure forms due to distinctive accumulation behavior. Particle interaction forces create porous aggregates, stabilize the aggregate as it contacts the deposit, and retain open pores. The effect of fine particles on properties of deposited mixtures is also analyzed. Results are relevant to understanding the formation of collapsible aeolian deposits on Earth and may contribute to the estimation of the physical properties of aeolian sediments on other planetary bodies. [ABSTRACT FROM AUTHOR]