Small-strain shear modulus (Gmax) and microscopic pore structure of calcareous sand with different grain size distributions

The maximum shear modulus (G_max) is a key material characteristic that is incorporated in advanced soil constitutive models. Numerous experimental studies have been conducted to describe the effects of particle sizes and packing characteristics on G_max. However, most of these studies were conducted on quartz-based sands. A review of the literature revealed that few studies have described the effects of grain size distribution (GSD) on G_max in calcareous sands. Therefore, bender element (BE) tests were performed on calcareous sands with different mean grain sizes (d₅₀), uniformity coefficients (C_u), and void ratios to obtain G_max. The BE results revealed that the G_max of calcareous sand increases slightly with increasing d₅₀ but decreases significantly with increasing C_u. A modified model of G_max incorporating the effects C_u and d₅₀ was therefore developed for calcareous sand. Moreover, microscopic observations of pore size distributions (PSD) obtained from nuclear magnetic resonance (NMR) tests were presented to demonstrate the effect of GSD on PSD and its correlation with G_max. The NMR results revealed that the interaggregate pore structure proportion and uniformity of the PSD decreased significantly with increasing C_u but increased slightly with increasing d₅₀. The underlying mechanism for the effect of GSD on G_max was related to its substantial impact on microstructure. The significant decrease in G_max with increasing C_u can be attributed to the remarkable reduction in the ratio of the interaggregate void ratio to the intraaggregate void ratio. Additionally, G_max was enhanced as the heterogeneity of the microporosity structure distribution decreased.

Graphic abstract