Frequency Effects on Damping/Modulus of Cohesive Soil

In order to assess the effect of frequency on the dynamic response of clay, a modified resonant column/torsional shear apparatus was employed to test undisturbed samples of marine clay at various frequencies. Details of the modified apparatus are described and test results over a wide range of frequencies at different strain levels are presented.

Results show that the dynamic shear modulus of samples tested by the resonant column was always greater than the dynamic shear modulus of the same samples tested at lower frequencies in torsional shear. To confirm that the increase in shear modulus was due to frequency (strain rate), samples were tested in torsional shear at various frequencies. Results indicated that the shear modulus always increased with frequency, though the effect was fairly minor.

No observable effect of frequency on damping ratio was measured for samples tested in either resonant column or torsional shear modes. As well, there was no significant variation in damping ratio for samples tested in torsional shear under various frequencies.

Significantly lower residual pore pressure response was measured for samples tested by resonant column than for those tested at a lower frequency in torsional shear.