Effect of overconsolidation ratio on dynamic properties of binary mixtures of silica particles

• Stress-history-based Gmax of binary mixtures of sand-sand particles and silty sands was measured.
• OCR exponent in the Gmax relationship was expressed in terms of stress exponents.
• The effect of OCR on Gmax increased with increasing size difference between small and large particles.
• The maximum stress history effect of tested material was observed at a FC≈5%.

Overconsolidated soils are ubiquitous in nature due to multiple mechanisms; however, the stress-history-based studies of small strain stiffness on binary mixtures, such as silty sand, are limited even though natural sand deposits are commonly mixtures of sand particles with varying amounts of fines. Consequently, this study quantified the stress-history-based dynamic properties of binary mixtures, such as sand-sand mixtures with different size small particles, and silty sand mixtures with small amounts of non-plastic fines, up to the critical fines content. By performing bender element tests on those mixtures according to fines content, size ratio, and overconsolidation ratio, the stress-history-based Gmax of binary mixtures was evaluated. For the relevant data analysis, the OCR (overconsolidation ratio) exponent in the Gmax formulation was expressed in terms of stress exponents during loading and unloading. It was found that the effect of OCR on the estimation of Gmax increased with a decrease in size ratio (or increase in size difference), since the stress exponents during loading increased more significantly with a decrease in size ratio due to the pronounced change in interparticle coordination between large grains. However, the variation of stress exponents during unloading of different mixtures was relatively small due to the prevalent elastic deformation. It was demonstrated that the maximum stress history effect of tested mixed soils was observed at a fines content of approximately 5%, which was smaller than critical fines content of silty sand. This behavior was attributable to the delay in critical fines content observed during unloading, when compared to that observed during loading.