Potential Influence of Particle Morphology Parameters on Cyclic Liquefaction Resistance of Rubberized Sands Under CDSS Loading

This experimental study investigates the influence of particle morphology parameters, specifically Roundness (R) and sphericity (S), on the liquefaction resistance of rubberized sand subjected to cyclic direct simple shear loading. The research evaluates the cyclic simple shear behavior of two distinct sandy soil types as: crushed angular sand and spherical dune sand mixed with granulated rubber at varying contents (0, 2.5, 5 and 7.5%). The experimental program has been conducted using a cyclic direct simple shear (CDSS) apparatus under three cyclic stress ratios (CSR = 0.12, 0.15, and 0.18). The obtained results show that incorporating rubber enhances the cyclic liquefaction resistance of the tested mixtures up to a certain threshold rubber content (R_B = 5%) for the sand types considered. At the optimum rubber content (RB = 5%), the CRR increased from 0.157 to 0.174 for crushed sand, corresponding to a 10.8% improvement in cyclic resistance, and from 0.128 to 0.151 for dune sand, corresponding to an 18.0% improvement. In addition, at CSR = 0.12, the number of cycles to liquefaction increased from 66 to 130 cycles for crushed sand (+ 97.0%) and from 26 to 55 cycles for dune sand (+ 111.5%). The maximum normalized dissipated energy also increased from 0.241 to 0.351 for crushed sand (+ 45.6%) and from 0.082 to 0.165 for dune sand (+ 101.2%). These values support the conclusion that the RB of 5% appears as the most effective rubber content within the investigated range. Additionally, results demonstrate that crushed sand-rubber mixtures exhibit lower values of particle morphological features, and hence; reflecting substantial impact of angular particle shape characteristics, which results in a higher cyclic resistance ratio (CRR) and maximum normalized dissipated energy (W_n−max) compared to those of the dune sand-rubber mixtures.