Experimental study on cyclic deformation properties of saturated Fujian sand at different loading frequencies

Abstract

In this study, a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction (shearing contractive (SC) period and initial shearing dilative (ISD) period) and post-liquefaction (late shearing dilative (LSD) period) deformation properties of saturated Fujian sand. The secant shear modulus G and damping ratio λ in the entire cyclic loading process, and the unloading tangent shear modulus GL1 and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude γa. The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent. However, all the G-γa, GL1-γa, and GL2-γa curves in the ISD and LSD periods showed a downward trend with an increase in f. This study also proposes a modified method for calculating λ to compensate for the analytical error caused by the non-closure of hysteresis loop. Compared with the classical curves that mainly applied in geotechnical engineering, the λ first increases and then decreases with the increase of γa. Furthermore, the λ evaluated by the modified method is approximately 10%–15% more than the λ evaluated by the traditional method when the λ reaches its peak value.

Keywords

• Sand liquefaction
• Cyclic loading frequency
• Hysteresis loop shape
• Shear modulus
• Damping ratio