A Numerical Approach for the Determination of the Primary Fabric of Granular Soils

Abstract

Granular soil as a porous medium consists of particles, touching each other and forming a solid skeleton with interconnected pores. The transfer of externally applied loads is in most cases not homogeneous, but takes place mostly in a limited number of particles creating so-called force chains. The assembly of force chains is frequently referred to the primary fabric of a soil. The knowledge of the primary fabric is of vital importance for the analysis of many soil behaviours as, for instance, in the assessment of suffusion. Most of the current numerical models, mostly based on a discrete element approach, generate an artificial soil specimen by creating particles randomly. Therefore, particle position is not under control at all, and as a consequence the influence from particle arrangement on the creation of the primary fabric is neglected. This paper presents a sequential packing method, which allows studying two different types of particle arrangements for a given and constant grain size distribution: (1) layer-wise, producing a layered structure and (2) discrete, leading to a rather homogeneous soil structure. The generated soil specimens are compacted using a discrete element model under oedometric boundary conditions and zero gravity to create force chains within the soil structure. These force chains are then analysed to determine the soil fraction contributing to the load transfer. The results of the study provide an evidence of the influence of the particle arrangements on the appearance of the soil skeleton and the fraction of particles involved.