Modeling of strain dependency of shear modulus and damping of clayey sand

A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Strain dependencies of shear modulus and damping were simply modeled. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered particularly in the large strain range. The consideration could be made by normalizing G with G' subscript 0 = AF(e)(sigma' subscript m/sigma subscript mr) superscript n, the initial shear modulus for the effective confining stress of that particular loading cycle, instead of using G subscript 0. G/G' subscript 0 was expressed by a function of gamma as G/G' subscript 0 = 1/(1 + b subscript g gamma) which was almost stress level independent for clayey sands used in this study. The damping ratio was not affected much by the confining stress. The strain dependency of the damping ratio was modeled by h = a subscript h gamma/(1 + b subscript h gamma). Effects of load irregularity on the shear modulus were also investigated. The excess pore pressure and the residual strain were generated especially when the major peaks in the irregular loading were applied to the specimen. However, G/G' subscript 0 for the irregular loading could be represented reasonably well by the average curve for the uniform cyclic loading if the excess pore water pressure and the residual strain were taken into account.