Primary fabric fraction analysis of granular soils

Abstract

Granular soil can be considered as a composition of two fractions of particles; an immobile part called the primary fabric, and loose particles located in the voids formed by the immobile part considered to be potentially mobile. The primary fabric transfers momentum through force chains formed by interconnected force chains. These force chains form pores where loose particles are located. As a consequence, loose particles can be mobilised very easily under the influence of seepage flow and transported away if the geometrical conditions of the pore structure allows it. Therefore, the determination of the primary fabric fraction, as well as loose particle fraction, is of vital importance especially in soil suffusion predictions, which must be thoroughly considered in the design of hydraulic structures or their risk assessment. This paper presents a new method to simulate the behaviour of soils under stress and introduces a numerical analysis to define the primary fabric fraction. To achieve this, soil specimens are built by a new sequential packing method, which employs trilateration equations for packing. Later, specimens are compacted under oedometric conditions using the discrete element method to observe how the loading force is distributed across the solid matrix and to identify the fraction of the soil sustaining the external force. The primary fabric fraction analysis is conducted on two types of soil particle arrangements with several grain size distributions. A striking finding of this study is that the portion of the soil belonging to the primary fabric greatly depends on the structural packing of the granular particles. This finding should be used as evidence for the formulation of more accurate criteria for the prediction of suffusion and erosion in the future.