Study on mechanism of particle aggregation and pore formation during loess air-fall deposition based on discrete element method

The pore structure of aeolian deposits is essential for predicting their mechanical properties and the climatic conditions during their deposition. The discrete element method (DEM) is a practical approach for analysing the formation and evolution mechanisms of aeolian deposits’ pore structure. However, the effect of particle shape and non-contact van der Waals force on deposits’ pore structure with different particle sizes needs further exploration to enhance the efficiency and accuracy of DEM simulations. We developed a VdwForce model for DEM that accounts for the van der Waals force's long-tail effect, and we conducted loess air-fall numerical tests that matched laboratory simulation tests. DEM simulations and laboratory tests show that the deposits’ porosity increased as the median particle size decreased, whether using spherical or actual shape particles in simulations. When deposits formed by particles with actual shapes have dense packing structures, simulations utilising spherical particles of the same size produce larger porosities. The primary reason of the alteration in the pore structure of the loess air-fall deposits is the shift in the quantity and pattern of particle agglomerates caused by van der Waals attractive force. So, the aggregation process during air-fall was essential for forming overhead pore structures.