UNCERTAINTIES OF SHEAR MODULUS REDUCTION AND DAMPING RATION CURVES OF MARINE SOILS

The uncertainties of soil shear modulus reduction (G/G_max) and damping (λ) increase curves with shear strain amplitude (γ_a) have important influence on the uncertainty of the results of nonlinear site seismic response. Based on the test data of undisturbed marine silty clay samples taken from seabed surface to 110 m depth at the Laizhou Bay, the G/G_max curve is described using the Davidenkov skeleton curve function, and the λ curve is expressed as a function of two variables, i.e., the λ_min (small strain damping) and G/G_max. The laboratory investigation reveals that the prediction equations of parameters A, B, and γ_r, which describe the G/G_max curve and λ_min, are all functions of the seabed depth H. The uncertainty transfer analysis based on point estimation method shows that the total uncertainty of the predicted G/G_max caused by the parameters A, B, and γ_r and the single univariate uncertainty of the predicted G/G_max caused by one of the three parameters increase first and then decrease with γ_a. The total and univariate uncertainty of the predicted G/G_max caused by the variable B or γ_r decrease with H, whereas the univariate uncertainty of the predicted G/G_max caused by the variable A increases with H. The total uncertainty of the predicted λ caused by G/G_max and λ_min and the univariate uncertainty of the predicted λ caused by G/G_max increase slightly first and then decrease slightly with γ_a, while both decrease slightly with H. The univariate uncertainty of the predicted λ caused by λ_min is independent of γ_a and increases slightly with H.