Effect of complex-grain-size curves on shear modulus degradation of calcareous sand

The dynamic shear modulus G and its degradation tendency G/Gmax are essential parameters for characterizing the dynamic properties of soil. Coastal facilities constructed on calcareous sand foundations are subjected to multiple types of cyclic loadings. To investigate the effects of the uniformity coefficient Cu, effective confining pressure σ0′, relative density Dr, and median grain size d50 on the dynamic G and its degradation rule for calcareous sand, a set of resonant column tests is conducted on calcareous sand with different grain-size-distribution curves. The experimental results clearly show that the G degrades faster for calcareous sand with a lower σ0′ and a larger Cu. By contrast, the degradation of the G is affected less by Dr and d50. The G/Gmax values decreased slightly as γ increased but remained less than 10−5, whereas the G/Gmax curve descended rapidly as γ increased beyond 10−5. Based on the test results obtained in this study and previously published data, a new mathematical model characterizing the degradation tendency of G/Gmax with respect to the shear strain level of calcareous sands with different gradation conditions is proposed. The relevant parameters associated with the proposed model are correlated with Cu and σ0′.