Volumetric strain accumulation for saturated coral sand under various cyclic loading patterns

Abstract

Seismic events and wave action can induce volumetric strain (ε_v) accumulation in saturated sandy soils, leading to damage to the ground surface and structures. A quantifiable relationship exists between the generation of ε_v in sandy soils under drained conditions and the development of pore water pressures under undrained conditions. In this study, the impact of relative density (D_r), cyclic stress path, and stress level on the characteristics of volumetric strain (ε_v) generation in saturated coral sands (SCS) was evaluated through drained tests employing various cyclic stress paths. The test findings demonstrate that the rate of ε_v accumulation in SCS is notably affected by the cyclic stress path. The rise in peak volumetric strain (ε_vp) in SCS, as a function of the number of cycles, conforms to the arctangent function model. The unit cyclic stress ratio (USR) was employed as an indicator of complex cyclic loading levels. It was determined that coefficient (ε_vp)_u is positively correlated with USR at a specific D_r. At the same D_r, coefficient C_N1 exhibits a positive correlation with USR, while coefficient C_N2 displays a negative correlation with USR, following a power-law relationship. Irrespective of cyclic loading conditions, ε_vp rises with an increase in generalized shear strain amplitude (γ_ga). A power function model was established to represent the relationship between ε_vp and γ_ga. The coefficient ζ₁ decreases as D_r increases. Comparisons were drawn between ε_vp and γ_ga for Ottawa sand and SCS. The results indicate that, as D_r of Ottawa sand increases from 30 % to 70 %, the coefficient ζ₁ decreases from 1.54 to 0.73, representing a reduction of approximately 53 %. In contrast, under identical conditions, the coefficient ζ₁ of SCS exhibits a less pronounced decrease, from 1.16 to 0.79, corresponding to a reduction of roughly 32 %. These observations suggest that variations in D_r have a more substantial impact on generating ε_vp in Ottawa sand compared to SCS.