The influence of undrained cyclic loading patterns and consolidation states on the deformation features of saturated fine sand over a wide strain range

Abstract

Undrained cyclic loading patterns and consolidation states can significantly affect the deformation features of medium-dense saturated fine-grained sand. A series of undrained cyclic loading tests with different consolidation states, i.e., various mean effective consolidation stresses (p0), principal stress direction angles (α0), ratios (R0) of major and minor principal stresses, and relative magnitudes of intermediate principal stress (b0), were performed on saturated micaceous fine sand specimens with a relative density of 50% corresponding to a wide strain range in the order of 10−5 to 10−2. The patterns of cyclic axial, torsional, and axial–torsional combined loadings were applied in a hollow cylinder apparatus. The small-strain shear modulus G0, the reference shear strain γr, curves for shear modulus reduction G/G0, the damping ratio λ and Poisson's ratio υ with increasing strain were determined. The results of the cyclic axial–torsional combined tests showed a close relationship between G0, γr, and υ as well as the consolidation state parameters p0, R0, α0, and b0. The G0 and γr increased nearly linearly with increasing p0 and with decreasing α0 or b0. The υ is strain dependent and increases as the p0 decreases. Tests indicated that the reduction of G with increasing shear strain γ became more pronounced as p0 increased. The relationship for the G/G0 versus γ/γr was approximately independent of the cyclic loading patterns and the various values of parameters p0, R0, α0, and b0. A slight difference is noted between the damping ratios λt and λz, corresponding to vertical and torsional deformations. An empirical model was proposed for the dependence of the increase in damping ratio characteristics on the deviatoric strain.