A quantitative evaluation method for granular skeleton state of binary soils at arbitrary relative density

The granular skeleton state relates closely to the mechanical behavior of granular soils but its characterization remains an open challenge. This study aims to develop a novel method to quantify the skeleton state of binary granular soils with arbitrary relative density Dr. Inspired by a linear correlation between the maximum and minimum void ratios, the dual-skeleton packing model was extended to incorporate the effect of Dr. A standard procedure of determining the dual-skeleton index ψ at arbitrary Dr was proposed. Furthermore, a series of numerical binary soil samples with 27 PSDs were simulated in multiple Dr via discrete element method (DEM). The results indicated that the granular skeleton state experienced a typical three-phase evolution pattern of “coarse-dominated → transitional → fine-dominated” with increasing fc. Through the calculated ψ value, critical fc values of phase transition in skeleton state evolution for samples with multiple Dr and the ratio of maximum to minimum particle diameter Rd were unveiled. The micro-mechanical behaviors were observed to be strongly related to the variation of ψ value. Furthermore, a quantitative correlation between ψ and the stress contribution of fine particles was revealed. The simulation results demonstrated the dual-skeleton index ψ can serve as an indicator to characterize the micromechanical behavior of granular media.