Experimental study of cyclic shear behaviour of silty soils in Yellow River Delta

The soil static and dynamic universal triaxial and torsional shear apparatus was employed to perform both undrained cyclic triaxial tests and cyclic torsional tests for undisturbed silty soil samples. Based on the experimental test results, dynamic characteristics of both deformation and strength of undisturbed marine silty soil is investigated. The maximum dynamic shear modulus and the dependency of dynamic shear modulus and damping ratio on shear strain are defined through cyclic triaxial shear tests. An empirical pattern is established for residual pore water pressure generated during cyclic shear which is represented by a hyperbolic function with respect to the number of cycles of dynamic stress. And an empirical formula is developed to describe the cyclic strength with respect to the number of cycles. The related parameters involved in both patterns of pore water pressure and cyclic strength are determined by experimental tests; and their dependency on the consolidation stress ratio is clarified. The experimental data achieved from cyclic torsional shear tests are used to validate the results from the triaxial shear tests. It should be more conservative using the cyclic strength determined by triaxial shear tests in geotechnical earthquake design.